Photochemical Activity and Ultraviolet Radiation Modulation Factors (PAUR II).

1. WORK CONTENT

1.1 Objectives and Goals

1.1.1 Main Objectives

The main objectives of this project are to measure and model UV-B spectral transmittance through turbid atmospheres and to study the role of stratospheric and tropospheric ozone in the UV-B transfer in the presence of aerosols. The following tasks are foreseen:

I: UV Modulating Factors.

The UV modulation by variations in stratospheric ozone and by tropospheric ozone due to enhanced photon pathlengths by scattering from different types of aerosols, the effect of which is also targeted, will be studied during a campaign in the southeastern Mediterranean.

II: Validation of UV models with large data sets.

An extensive analysis and interpretation of data will be performed, together with modeling of UV-B transfer codes and validation of model calculations with a large and calibrated data set. UV irradiance and actinic flux measurements are to be compared to model calculations, in order to assess the capabilities of radiation models to reproduce the radiation field for the conditions encountered during the campaign. These studies will focus on (a) the effect of tropospheric aerosols of different physical, optical and chemical characteristics on UV-radiation, by comparing spectral measurements and model calculations with and without aerosols and perform Mie scattering calculations to define the optical properties of aerosols and (b) will investigate the effect of altitude change of spectral UV-radiation and sensitivity of spectral UV-radiation with respect to the altitude gradient and concentrations of tropospheric ozone.

1.1.2 Side Objectives

These objectives arise from the evidence of high background tropospheric ozone found in PAUR to exist in the area of study. These include studies of the mechanisms maintaining the enhanced tropospheric ozone in the Aegean and interrelationships with the UV radiation field. Photochemistry, with emphasis on the oxidizing capacity and maintenance of high ozone over southeast Europe, and the modeling of factors determining ozone formation in the presence of aerosols and steep gradients of JO(¹D) will be also studied.

1.2 Project Methodology

The project has been divided in three major workpackages which are described below and are summarized in Table 1.

Workpackage 1:

Task 1.1: Selection of sites and preparation of the campaign

During the first year of the project there will be a survey for selecting the measuring sites in Crete and Lampedousa and for preparing all the necessary technical and logistic arrangements at both places. The results of this survey will be based on the following criteria (1) exposure conditions (2) accessibility (3) height difference between sites (4) lack of influence from local air pollution sources and (5) presence of alternating maritime and Sahara aerosols. Also the results and the experience from the PAUR I campaign will be used as guidelines, but will help to avoid duplication of efforts. All participating groups will maintain and calibrate their equipment for the campaign.

Pre-campaign preparations of field equipment installation include (a) packing, shipping and installation of the equipment to Crete, Lampedousa and other observational sites (b) set up, calibration and testing of all equipment. All the radiometric instruments will be checked for comparability before, during and after the campaign with a traveling calibration unit. In addition before and after the campaign the radiometric instruments will be brought together at the same site for a two days intercomparison.

Task 1.2: The Mediterranean (Aegean) Campaign

An extensive 45-day campaign in the south and southeastern Mediterranean is planned at three sites. Two sites are located in the island of Crete, one at high altitude and one at low altitude, and one in the island of Lampedousa. In addition, radiation and surface ozone measurements, as well as vertical ozone and aerosols profiles will be obtained with the LAP-AUTH LIDAR system in Thessaloniki, in order to support the objectives of the campaign. Additionally, O₃, NO₂ and SO₂ Brewer measurements will be performed in Rome. The measurements during the Campaign also include optical characterization of aerosols, spectral UV-B measurements, ancillary radiation measurements and atmospheric composition measurements on top and bottom of the mountain, assisted by LIDAR ozone and aerosol profiles. In situ measurements of ozone and UV irradiance will be performed on board of two vessels cruising across and along the Aegean sea during the campaign. The experiment is planned for 45 days during the period from May through June 1999, which satisfies the presence of alternating aerosol characteristics. This is because May and June are months with alternating etesians (north) winds and southern (Saharan) winds in south Aegean.

The equipment foreseen for the various sites involved in this campaign is described in the following:

Crete

One double-monochromator Brewer spectrophotometer will be installed at the top of the mountain to measure global and direct spectral UV irradiances from 285 through 366 nm at a resolution of 0.55 nm (4% accuracy), along with total ozone, columnar SO₂. From the direct measurements aerosol optical depth can be derived with an accuracy better than 10% (LAP-AUTH).

One broadband YES UV-B pyranometer will be used to measure the UV-B dose with 1-minute time resolution (LAP-AUTH, IASB).

Measurements of short-wave solar radiation will be performed with a pyranometer with 1-minute resolution, in order to record short-term fluctuations due to cloud cover (IASB).

One wavelength band (UV-B) nephelometer (DUTH)

Sun photometer to determine the attenuated direct sunlight and sky radiance at different wavelengths including UV-B (DUTH).

A laser in cavity particle size analyzer (6 size bands from 0.1im to 6 im) (DUTH)

High Volume, Dichotomous Vitrual Impactor (DUTH)

An aethalometer to determine the black carbon atmospheric concentrations (DUTH)

One SANOA DOAS spectrometer measuring O₃, NO, NO₂, HNO₂, CH₂O, toluene, xylene, benzene and naphthalene which will be modified by the addition of a 30 cm diameter telescope for increasing the length of the optical path to 1 km and thus the sensitivity of the measurements to sub ppb levels for each species (CNRS-SA).

One SAOZ, zenith sky / direct sun UV-visible spectrometer similar to those at NDSC stations measuring total ozone (1% precision, 3% accuracy) and NO₂ (5% precision, 10% accuracy) (CNRS-SA).

One automatic meteorological station continuously measuring air temperature, relative humidity and wind speed and direction (UMUN, DUTH, IASB).

Surface O₃ measurements will be obtained with a conventional ozone analyzer. The detection limit is around 1 ppbv and the time resolution can be better than 1 min (UMUN).

A luminol instrument will be used for NOx measurements. The instrument has a detection limit of approximately 5 pptv and the time resolution of the instrument is around 5 min (UMUN).

A luminol instrument will be used for PAN measurements. The instrument has a detection limit of approximately 5 pptv and the time resolution of the instrument is around 5 min (UMUN).

The measurement of C₄-C₁₂ species will be accomplished with a commercially available Siemens GC/FID system that is capable of separating and quantifying about 50 different species with a detection limit of around 20 pptv for most species and a time resolution of 30 min. The system is equipped with two columns (25 m / 0.25 mm WCOT-CP-Wax-CB and 25 m / 0.32 mm WCOT-CP-Sil-CB). 0.5-1.0 lt of air are retained on an absorbent (Porapak Super Q^TM) and injected subsequently after cryofocusing. Methane, alkanes, alkenes, alkines, aromatics (Benzene, toluene, xylenes and others) together with some biogenic HCs (limonene, cumene) will thus be measured (UMUN).

For the J-NO₂ measurements a 4-pi radiometer originally developed for use in the EUROTRAC/TOR programme will be used. The radiometer determines the rate of the in-situ NO₂ photolysis via a continuous measurement of the actinic flux in the appropriate wavelength of the 4pi-sr-hemisphere. Modifications such as the use of quartz diffusers minimize the dependence of the output signal on solar zenith angle. The detector is a Hamamatsu Head-on vacuum Phototube. The absolute calibration is better than +/- 5% with respect to a chemical radiometer (METCON).

For the J-O(¹D) measurements a filter radiometer will be used. The precision of the instrument is better than 5% while the absolute calibration, based on comparisons with chemical actinometry of spectroradiometry is around 20% (METCON).

Site II (Bottom of the mountain):

Radiometric, aerosol (physical, chemical and optical characteristics) and air quality measurements will be performed at the bottom of the mountain with identical instrumentation as on the top of the mountain (i.e. UV-B dose, J's, hydrocarbons, ozone, NOx, total radiation, aerosol properties). The following instruments will be additionally operating during the campaign:

A modified OPTRONICS OP 754 spectroradiometer with a spectral resolution of about 1 nm will be used to perform spectral measurements of solar irradiance in the UVB - UVA and visible up to 600 nm at the bottom of the mountain. The instrument has a 2pi field of view and a very good cosine response (IASB).

Aerosol LIDAR (VELIS) for the range resolved detection of tropospheric and stratospheric aerosols at 532 nm (CNR).

The EPFL-DIAL is equipped with two Nd:YAG lasers combined with Raman cells. The wavelengths at 289 nm and 299 nm are used to measure the differential absorption induced by the atmospheric ozone concentration, while the less absorbed wavelength at 299 nm is used as a probe of the vertical aerosol extinction coefficient. The LIDAR signals are collected on two separate telescopes, one for the short range (50 m to 500 m) and a second for the long range (500 m to 5 km). The vertical resolution of the measurement is 15 m to 150 m and the averaging time is typically less than 3 min. Depending on visibility conditions the accuracy is 10 % to 20 % EPFL).

Lampedousa (Site III)

The island of Lampedousa is located in central Mediterranean between Sicily and west Libya, particularly susceptible to Sahara dust transfer will be near the sea level and will support those from the island of Crete. The measurements at Lampedousa are described as follows:

Deployment of a portable lidar system for the troposphere and lower stratosphere. The system will use a 50 cm telescope, and will allow to derive the aerosol backscattering profiles in the troposphere at 355 and/or 532 nm. The aerosol depolarization ratio will be also measured (ENEA-CNR-UOR).

Monitoring of the total ozone and UV irradiance by means of a double monochromator Brewer instrument (ENEA-CNR-UOR).

Measurements of the CO₂ concentration at the ground will be carried out continuously. These observations, together with the weekly measurements of other greenhouse gases, will provide additional information useful to characterize the air masses (ENEA-CNR-UOR).

C. Cruising Vessels

One vessel will be cruising in the central Aegean from west to east and the other vessel form north to south, to provide information on the spatial distribution of surface ozone and global UV irradiance in the area.

Two ozone analyzers will be installed on two different cruising vessels (LAP,UMUN,DUTH).

Two multifilter radiometers will monitor global UV irradiance at 4 wavelengths (IASB).

D. Thessaloniki

At Thessaloniki the following measurements will be performed during the campaign:

Measurements of the vertical distribution of ozone and aerosols in the lower troposphere in the 0.7-10 km range, will be performed with a Differential Absorption Lidar (DIAL) system by Partner A. The DIAL system is equipped with a Nd:YAG laser which primary emits at 1064 nm and simultaneously through harmonic generators emits the second and fourth harmonic, at 532 and 266 nm respectively. The fourth harmonic of the Nd:YAG laser pumps optically a high pressure Raman cell containing H₂ and D₂, which permits the generation of laser wavelengths at 266 nm, 289 nm, 299 nm and 316 nm. A 500 mm Newtonian telescope is used for the collection of the backscattered radiation. The backscattering signals at 266nm, 289 nm and 299 nm are used to calculate the ozone vertical profiles in the 0.7-10 km range, while for the vertical distribution of the aerosol extinction coefficient the backscattered signal from 316 nm is used. The optical separation of the relevant LIDAR signals is obtained with a grating multiline spectrometer. The temporal resolution of the system is of the order of 1-2 min and the spatial resolution 15-200 m. The measurements accuracy for ozone is ± 10% and for the aerosol is about ± 20%. The system can perform both daytime and nighttime measurements.

One single-monochromator Brewer spectrophotometer to measure global and direct spectral UV irradiances from 290 through 330 nm at a resolution of 0.55 nm along with total ozone, columnar SO₂ (LAP-AUTH).

One Brewer spectrophotometer will be operating at Rome during the campaign providing total ozone, columnar SO₂ and NO₂ measurements, in order to support the observations at Lampedousa.

F. Post campaign activities

The post campaign activities include experiment tests and calibration checks and the preparation of an instrumentation log and a quality assurance / quality control report at the end of the campaign.

Work Package 2: UV modulation by aerosols, clouds and tropospheric ozone

This Workpackage aims at interpreting the results from the measurements obtained during the campaign as described in Workpackage 1. In order to identify the significance of the parameters modulating UV, the following tasks have been identified:

Task 2.1: Aerosol optical characterization and other modulators of UV-B.

This task will provide the aerosol optical characteristics, by comparing the downwelling radiation at two altitudes from which the aerosol spectral optical thickness and radiation transmission through a slab of atmosphere will be derived. Cross calibrated radiometers will be located at the top and bottom of an isolated mountain in the Mediterranean which will provide a measure of the radiation transmission through the slab. An aerosol LIDAR will also provide vertically resolved profiles of aerosol backscatter cross sections. Aerosol chemical properties will be determined from aerosols collected by two inter-calibrated high volume virtual impactors (2.5 im diameter and cut-off) at the top and the bottom of the mountain. Size distribution at the range between .1-.3im, .3-.5im, .5-1.0im, 1.0-2.0im, 2.0-5.0im and >5.0im will be determined with a six-channel laser in cavity optical counter. Light scattering at 532 nm will be determined using a nephelometer. Both optical counter and nephelometer together with a carbon black analyser will provide support for the aerosol LIDAR. The selected location offers the possibility of many cloudless (control) days during the experiment. The measurements will be analyzed for empirical correlations. The radiative transfer theory will be then utilized to determine the relationships between aerosol properties, the observed radiation field and the modeled radiation field to arrive at a physically consistent result. The resulting aerosol optical properties will be the best-estimate deduction of the aerosol radiative properties (i.e. albedo of single scattering and asymmetry factor, or refractive index and phase function) available at the time of the experiment. Other non-ozone absorbing gaseous constituents such as SO₂ and NO₂ will be determined and will be included in the modeling to establish their effect in new particle formation and/or their effect on aerosol optical and chemical properties.

Task 2.2: The effect of tropospheric ozone in the presence of Sahara / Maritime aerosol on UV transfer

Moving to the tropospheric ozone issue, this(second) task will be accomplished using data from the same extensive experiment (WP 1). The rationale comes from earlier literature suggesting a disproportionately large role of tropospheric ozone in UV absorption (relative to stratospheric ozone) because of the enhanced photon pathlengths from tropospheric scattering. The reverse can also occur, depending on the solar zenith angle and ozone profiles. Of course the importance of tropospheric ozone in UV-B transfer or essentially the photon path enhancement, is difficult to be estimated because it depends on the precise angular distribution of the radiation field in the presence of aerosols (and clouds) which compound the issue. At present only few measurements exist linking UV with tropospheric ozone and good quantification has not been achieved. This second task of WP 2 will include further analysis of the measurements and modeling of various UV radiation quantities such as global, actinic flux etc., as a function of altitude, within a well defined atmospheric composition environment. Use will be made of the aerosol characterization and related atmospheric composition measurements. Specifically ozone profiles will be taken with LIDAR and in situ measurements with extreme caution as to be most useful for the interpretation of UV measurements. Special attention will be given to diurnal (e.g. upslope / downslope) circulation and its effect on the ozone profiles. Clear sky measurements will be emphasized along with the characterization of surrounding aerosol and ozone profiles. In this task interpretation of the data will focus on absolute measurements (e.g. spectral irradiances) as well as comparison with model predicted quantities (e.g. diffuse/direct ratio spectrum) from which quantities such as photon pathlength can be derived. The final results of this task will advance substantially our understanding of how tropospheric ozone modifies environmental UV radiation in the presence of variable aerosol and clear skies.

Task 2.3 Interpretation of meteorological observations and modeling

Analysis of the meteorological parameters measured during the campaign will be performed. Modeling and mathematical techniques will be used to study the air history in the area of interest and to infer remote sources of important atmospheric pollutants. This task will be realized with the following modeling approach.

Use of a mesoscale numerical model (MIUU) to predict the 3-D wind fields and boundary layer processes relevant to the regional transport of atmospheric pollutants in the Mediterranean.

Calculation of air trajectories both in forward (source-oriented) as well as in backward (receptor-oriented) mode.

This task will provide also synoptic meteorological conditions and characterization of air masses during the experiment as well as a consultation in the climatology of the region.

Task 2.4: Calculations of UV spectra and of J values and their modification by particles, clouds and ozone

This task includes an extensive analysis and interpretation of data and modeling of UV transfer codes and validation with QA/QC data. The studies in this work package will compare UV irradiance and actinic flux measurements with model calculations to assess the capabilities of currents radiation models to reproduce the conditions accoutered during the campaign. Calculation of solar fluxes and photodissociation rates in the region will be performed with radiative transfer models which accurately calculate photodissociation rates in the atmosphere at different locations, different solar elevation and different atmospheric conditions in which clouds and particles are included in the calculation scheme.

The radiation measurements will be analyzed for empirical relationships to each other and radiative transfer theory will be used to determine the relationships between aerosol properties, the observed radiation field and the modeled radiation field to arrive at a physically consistent result.

Mie scattering calculations will be performed in order to obtain the optical properties of Sahara type and marine type aerosols. The effect of different single scattering albedo and asymmetry parameter values, based on the calculations mentioned before, on the spectral UV radiation and on the J values will be investigated with the use of advanced radiative transfer models. The effect of altitude and changes in tropospheric ozone concentration will also be investigated.

Task 2.5: Comparison of calculated with the observed spectral UV-field

Data analysis of the spectral UV irradiance measurements will be performed and compared with radiative transfer model calculations, in order to validate the model with the data set obtained from the campaign. The effect of tropospheric aerosols on UV radiation will be investigated by comparing measurements with model calculations with and without the presence of aerosols. The radiation models used in this project will be further checked and validated by participating in planned intercomparisons of radiative transfer codes. The calculated photolysis rates for ozone and NO₂ will be compared with observations. Such comparisons are of importance since they will tell us how well we can model the photodissociation of key compounds in the oxidation process and the variation with ozone column densities

WORKPACKAGE 3: Modeling of chemical activities with particular emphasis on the oxidation capacity and ozone formation.

Model studies will be performed by UiO, of the large scale regional ozone formation and distribution as a result of variations and long term changes in the column densities. Analysis of the ozone column densities and the variation in ozone column densities performed as part of the project will be used as an input to the calculations of the photodissociation rates used in the chemical model. Calculations of the photodissociation rates will be performed where it is taken into account the changes in the ozone and particle level.

UiO will use a new version of a 3-D CTM which has been used to study distribution and formation in the troposphere from natural and anthropogenic processes. The new version of the model which has been tested out and will be used for future ozone studies. It has an extensive ozone chemistry and calculate the diurnal variation of approximately 50 chemical compounds, and is constructed to study ozone generation both in the background and in the polluted atmosphere. The model is a 19 layer model, and it can be run with different horizontal resolution: T21/T42 or T63, corresponding to 5.6, 2.8 and 1.9 degrees respectively. It uses transport data and other relevant physical parameters from analysis of ECMWF data. The study will be performed as a two step process. Firstly version T21 will be used to perform long term iterations (a year or more), in order to obtain a background field of the chemical compounds. The T42 and T63 versions will then be used to perform runs for the shorter periods which be selected for studies. A typical time period for this study will be the time of the campaign plus a spinup time. Tests have shown that 14 days are sufficient for spinup. The distribution obtained in the run with the T21 version will be used as input data for the finer resolution model studies. In both types of studies, the analysis for the selected periods will be focused on the European region and transport to and from the European continent. Approximately 50 chemical components are included in the scheme, which is used in the tropospheric models. The chemical scheme has both natural (isoprene) and anthropogenic HC source gases. Use will be made of an accurate and time efficient radiative scheme for calculations of photodissociation rates in the atmosphere.

In order to quantify how different factors contribute to the enhanced ozone levels observed, the following tasks are identified:

Task 3.1: Provision of emission data for ozone precursors (NOx, CO, hydrocarbons), and prepare transport data for the CTM study

UiO will prepare meteorological input data to be used in the 3-D CTM. These data are derived from analyzed ECMWF data for the particular periods that will be studied. Of particular interest for the project is that a new scheme for boundary layer processes is introduced that gives better representation of the transport of the gases in the boundary layer and the exchange between the boundary layer and the free troposphere. Global emissions will be taken from the GEIA data base which provide data on a 1 by 1 degree resolution. In addition, European emission data are available through the European Environmental Agency for different years.

Task 3.2: 3-D CTM studies of ozone generation

Model studies will be performed for the time period of the campaign. Model studies will also be performed for two other time periods in order to study ozone formation under different atmospheric conditions. The studies will include sensitivity studies of changes in dissociation rates (UV-B fluxes) based on the results obtained in WP 2 and this work package. The studies will focus on the ozone generation process, what are the conditions that favour the build up of high ozone levels over the regional, and what are the contribution from regional formation of ozone compared to the transport from surrounding polluted regions. These studies look at how the emissions of precursors (NOx, CO and hydrocarbons) affect the ozone formation process, and how they are transported to the region. Photolysis rates adopted for the modeling of the chemistry will be those obtained after quality control from the campaign measurements.

Task 3.3: Comparison of modeled distributions of ozone and precursors with observed distributions.

The model calculations will be performed for the specific time period when observations will be performed with real wind, temperature and precipitation data. Actual ozone column data for UV flux calculations will also be used. The modeling experiment offers therefore an excellent opportunity to validate and improve the model performance through comparisons with key chemical species which are observed during the campaign. Comparisons will be done with the following chemical components which are calculated in the model: surface ozone, NO, NO₂, CH₂O, different hydrocarbons (toluene, xylene, C₄ and C₅ compounds) and PAN. All these species are important in the ozone formation process. These comparisons can also give valuable information on how well the transport and the source distribution of the gases are represented. But first of all comparisons of modeling results with observations of the above gases are valuable for the analysis of the modeling results of the importance of the different sources for the ozone generation process.

Task 3.4: Ozone transport and enhancement in the Aegean region

The ozone measurements on board the vessel cruising from the west to the east Aegean will be used to determine the transport of ozone to the region during the period of campaign when the etesian winds are dominant. The possible enhancement of ozone concentrations, moving from urban to rural areas will be monitored with the vessel cruising from central to south Aegean, downwind of the etesian flow. These measurements will be used as input and/or comparison to modeling studies which describe on regional and subregional scale the enhancement of ozone downwind from the urban plumes. The current research will employ a modified version of the UK Photochemical Trajectory Model (UKPTM). The UKPTM describes the regional scale formation of ozone, PAN and hydrogen peroxide in a moving parcel of the boundary layer, and it is a receptor oriented model. These simulations will include in particular estimates of the primary pollutants and the formation of secondary pollutants in particular ozone in the Aegean and its contribution to larger scale ozone formation.

1.3 Milestones

The major project milestones result from the different objectives and workpackages of the proposal. As mentioned in the introduction of great importance to the success of the project is the flawless execution of the campaign in the islands of Crete and Lampedousa which will provide a large and calibrated data set to be used in different workpackages described before. Therefore the period from the pre-campaign preparation which should start already in April of 1998 at the latest to the campaign period in May / June 1999 and the post campaign period (July 1999) with the QA/QC of the large data set is the first milestone of this research. A second milestone can be placed at the end of 1999 when the first results from the chemical and radiative model calculations and validations will be ready. At the end of the project's first year an interim report to the EC will be delivered, presenting the activities and the preliminary results obtained up to this point. During the second year of the project the modeling studies will continue and the final results are expected to be ready by the end of the project. The last milestone is the compilation of the final report. The chart below indicates the proposed time scales foreseen for the individual work packages and tasks.

It should be emphasized that quality assurance and control criteria will be applied to all instrumentation and all data sets before and after the campaign. An extensive instrumentation log with instrument performance and accuracy estimates of data will be available for review at the mid-term meeting. The final report will include all major achievements obtained during the project. These milestones are important because they refer both to the creation of a reliable, unique data base on aerosol, chemistry and UV and also for reviewing of both the data sets and validating the models.

2. Role of the Participants

The scientific groups mentioned in the work content, which are involved in this project, are as follows:

PARTNER A: Laboratory of Atmospheric Physics, Greece (LAP-AUTH)

The main role of LAP-AUTH in the PAUR II proposal is to examine the disproportionate role of tropospheric ozone in selectively absorbing UV-B in the presence variable aerosol and to co-ordinate the overall project. LAP-AUTH will be involved in the WP2 described previously, as follows:

LAP will execute and implement spectral UV-B measurements during the campaign as well as atmospheric composition measurements from ground-based and LIDAR instrumentation

LAP will apply UV-B transmission theoretical models under representative environmental conditions, to asses scenarios of spectral UV-transfer as described in the main objectives .

LAP-AUTH is also responsible for providing statistical analysis of data available for the PAUR II .

LAP-AUTH shall undertake the collection and dissemination of meteorological measurements from the Greek Meteorological Service.

More specifically LAP will perform an extensive analysis and interpretation of data together with modeling of UV-B transfer codes and validation of model calculations with a large and calibrated data set. UV irradiance and actinic flux measurements will be compared to model calculations, in order to assess the capabilities of radiation models to reproduce the radiation field for the conditions encountered during the campaign

LAP shall provide the following instrumentation:

Brewer monochromators (X2).

One DOAS system for NO₂, O₃, SO₂, CH₂O, HC

LIDAR ozone and aerosol measurements.

Surface O₃ and NO_X analyzers.

Collection of Meteorological and air quality measurements

Conventional UV broad band meters.

Key Scientists, Professor C.S. Zerefos, Assistant Professor A.F. Bais, Associate Professor I.C. Ziomas, Dr. K. Kourtidis, Dr. K. Tourpali, Dr. D. Balis, MSc E. Kosmidis, C. Meleti, S. Kasadzis, E. Galani

External Assistance

Dr S. Madronich from NCAR and Dr. John De Luisi NOAA will provide external assistance in the theoretical and experimental aspects of the project.

ASSOCIATED PARTNER A1 TO PARTNER A: Service de Aeronomie, Centre Nationale de Recherche Scientifique France (CNRS-SA)

The contribution of the Service d' Aeronomie to the project will be focused at:

the measurement of the local concentrations of O₃, NO_x and VOCs at the two altitude levels selected in Crete by long path optical absorption (DOAS),

the related diurnal variation of the O₃ and NO₂ total columns by zenith sky uv-vis absorption spectroscopy at sea level, and

the interpretation of the measurement by box trajectory model simulations.

Two types of instruments will be used:

two SANOA DOAS spectrometers, already used during MEDCAPHOT and PAUR 1 for measuring the local concentration of O₃, NO, NO₂, HNO₂, CH₂O, toluene, xylene, benzen and naphtalene, which for this specific application will be modified by the addition of a 30 cm diameter telescope for increasing the length of the optical path to 1 km and thus the sensitivity of the measurements to sub ppb levels for each species;

one SAOZ zenith sky / direct sun UV-visible spectrometer similar to that running permanently at several NDSC stations such as the Observatoire de Haute Provence in France, able to measure total ozone (1% precision; 3% accuracy) and NO2 (5% precision; 10% accuracy).

The model to be used is a box photochemical model which will be run on backward trajectories and from meteorological fields, which will allow to simulate the O3 / NOx / VOC evolution in the air mass during 24 to 48 h before reaching the observing sites. The two instruments SANOA and SAOZ have been developed at the Service d'Aeronomie. The first, SANOA, now commercialized by the French firm Environnement SA, is in use at a number of Air Quality monitoring networks. It has been used for the measurement of the concentration of the nine species already quoted in the city and the suburbs of Athens within the frame of the MEDCAPHOT-TRACE project in 1994 and PAUR in 1996. Its extension on a longer path of 1 to 2 km has been tested successfully in the laboratory. The second, SAOZ, is in permanent operation at 19 stations in the world. Its performances have been tested and evaluated during several intercomparsion campaigns in 1992, 1994 and 1996 within the frame of the WMO and NDSC ozone and stratospheric change monitoring networks. The tropospheric photochemical box model, presently under development at the laboratory, is derived from the model successfully used for simulating the NOx, ClOx, BrOx and iodine stratospheric chemistry during the SESAME European stratospheric ozone campaign.

Key Scientists: Dr J.P. Pommereau (PI), Directeur de Recherche at CNRS, Dr Florence Goutail, Ingenieur de Recherche at CNRS, Dr Manuel Nunes-Pinharanda, Ingenieur de Recherche at CNRS, O. Antivilo, graduate student

ASSOCIATED PARTNER A2 TO PARTNER A: Institute d' Aeronomie Spatiale de Belgique, Belgium (IASB)

A - IASB will produce :

Total spectral measurements with a field of view of 2 p sr, in the UVB, UVA and visible (up to 600 nm) ranges of the solar spectrum, (the instrument has a practically perfect cosine response).

Direct and diffuse spectral data in the UVB, UVA and visible (up to 600 nm) ranges of the solar spectrum on the same time scale than total spectral irradiances.

Integrated data on UVB, UVA and total (up to 3 m m) one mean measurement every minute. The UVB integrated data will be presented in energy and effective energy.

Narrow band integrated data in the UV range (305 nm, 320 nm, 340 nm and 380 nm, with bandpath of around 10 nm) + a par channel (400-700 nm)

Basic meteorological data’s

Ozone total column deduced from the GUV instrument

Spectral data could be also reconstructed from the narrow band measurements.

B - IASB will participate to the campaign in Crete at see level.

The following instruments will be deployed in order to provide the most accurate

picture of the UV-Visible radiation field.

1 Spectro-radiometer (Modified Jobin-Yvon HD10).

This instrument will measure the solar UV-Visible spectral irradiance (280 - 600 nm) with a field of view of 2p sr, 1 scan every 15 minutes for solar zenith angles smaller than 100°.

1 Spectro-radiometer (Optronics 754) modified to measure synchronously the direct solar spectral irradiances on the same wavelength range than the Jobin-Yvon.

From the direct irradiance, it will be possible to estimate the optical depth of the

atmosphere and to estimate the characteristic parameters of the aerosol layer.

Combination of the measurements of these 2 spectroradiometers will provide total, direct and diffuse determinations of the solar spectral irradiances (180-550 nm) during all the campaign.

Moreover some other instruments will be deployed on the same site:

1 GUV 511-c filter radiometer (4 channels) or a NILUV filter radiometer (5 channels)

The interest of this instrument is double 1) the possible determination of the total

Ozone column and 2) an easy way to control the quality of the spectra data by

comparing the spectral data convoluted by the relative response of each channel and the measurement of the channels themselves.

Ancillary instruments as UVB meter (Yankee Environment System - YES) and Total Pyranometer (YES)

The UVB meter will provide data in energy (W m^-2) and in effective energy (weighted

by the erythemal action spectrum). These broadband instruments will moreover offer an other opportunity to validate the spectral data.

Finally, a 5 parameters (Temperature, Pressure, Wind Direction, Wind Speed and Relative Humidity) mobile meteo station will also be available.

C - IASB will participate to the exploration of the Crete site and will made some preliminary measurements during this one week pre-campaign in order to estimate the mean UV fluxes and meteorological conditions in Crete during May-June. These information will be useful to all teams for the preparation phase of PAUR II campaign.

D - IASB will also participate to

the comparison of the UV-Visible spectral data,

the interpretation of the effect of different type of aerosol,

as well as in the modeling tasks in connection to the UV penetration in the atmosphere.

A pseudo-spherical DISORT (discrete ordinate model) model is available at the institute; a simplified version of the same model will be available during the campaign for comparison and validation purposes.

E - IASB will also participate to the different scientific meetings and production of reports and papers in connection with the PAUR II project.

Key Scientists, Dr. Didier Gillotay , senior scientist (Chef de Travaux), Dr. Bruno Walravens, post-doctoral scientist, David Bolsee, physicist, Dr. Jean-Francois Muller, post-doctoral scientist, Dr. Philippe Peeters, post-doctoral scientist. Technical staff (mechanics and electronics) will also be involved in the project.

ASSOCIATED PARTNER A3 TO PARTNER A: Meteorologie Consult GmbH Germany (METCON).

METCON will take part in the field experiments and in the calibration exercises of the project according the workplan with the spectrometer equipped with two 2-pi-input devices and with two fast filter radiometers. The spectrometer system will be equipped with automatic shutters in order to resolve separate signals from the two input devices.

The devices used in the project will be cross-checked before the installation at the two sites as stated in the workpackage 1. The measurements will be performed continuously throughout the experiments. The measuring rate will be basically in half second intervals. Longer averages are calculated from these basic data. The instruments will be calibrated with our standard and with the chemical actinometers in Julich (J(O1D) and J(NO2)) as well as with the double monochromator. The instruments will be characterized before and after the experiment. Using a radiation model and the characteristics of the devices, the date from the two devices can also be interpreted for other selected regions of the spectral range between 290 nm and 450 nm.

Key Scientist Dr. Rainer Schmitt

SUBCONTRACTOR A4 TO PARTNER A: National Technical University of Athens, Greece, (NTUA)

The major contribution of the Laboratory of Lasers and Applications (LA) of the National Technical University of Athens (NTUA) to the PAUR II Project will focus on:

Provision of scientific and technical assistance (optolectronics and mechanical components) to the LIDAR groups during the Campaign.

Provision of expertise in the analysis and evaluation of the LIDAR, photochemical and meteorological data acquired during the Campaign.

Key Scientists, Lecturer Dr. A. Papayannis (Principal Investigator)

Assoc. Prof. Dr. A. Serafetinides

PARTNER B: University of Munich, Germany (UMUN)

UMUN will participate the Mediterranean (Aegean) Compaign and provide continuous ground-level measurements of key constituents relevant to photochemical ozone formation and mechanisms maintaining enhanced tropospheric ozone levels in the Aegean. These include ozone, PAN, NO_x, C₄-C₁₂ hydrocarbons along with pertinent meteorological parameters, such as temperature, humidity, wind, and radiation.

Two stations will be equipped and maintained throughout the campaign, i.e. the mountain station and the valley station on the isle of Crete, as selected by the coordinator.

All parameters will be measured with high resolution with respect to time (averages for 10 minute intervals or shorter if required) in order to resolve diurnal variations. Commercial instruments will be used for Ozone (UV-absorption), NO_x and PAN (Luminol) as well as meteorological parameters. C₄-C₁₂ hydrocarbons will be measured quasi-online by means of a GC-FID system operating in a 20 minute automatic cycle. All instruments have been used in previous field experiments, such as MEDCAPHOT-TRACE and PAUR-I, and meet high QA/QC standards.

UMUN will make all results obtained accessible to all partners in the project, for further modelling and interpretation studies. UMUN will contribute to the overall scientific objectives by participating in the scientific interpretation of both field measurements and model results.

Key Scientists, Prof. Dr. Peter Fabian, Director, Dr. Gert Jakobi, Dr. Bernhard Rappengluck, Dr. Herbert Werner, Dipl.-Phys. Heinrich Reitmayer

PARTNER C, Demokritus University of Thrace, Greece (DUTH)

DUTH will contribute to the project as follows:

To determine the atmospheric number concentration, mass loading, chemical composition, and optical characteristics of the aerosol. To apportion the relative contribution of different aerosol types to the radiative properties of the aerosol for the site and time of measurement

To relate the parameters determined in (A) with three dimensional air mass trajectories for the area and supply data to the aerosol models of the University of Oslo to confirm aerosol atmospheric evolution and radiative properties

To establish whether the properties determined under (A) and related to (B) can be related to chemical composition at the top and/or the bottom of the site and hence establish the homogeneity of the atmospheric slab whose radiative properties we are trying to establish

To assess the relation between the properties determined under (A) and the actinic flux measurements during the project. Also asses the effect of these properties on the photon path length enhancement.

Deployment of instruments:

1. Two high Volume Virtual Impactors with aerosol size cut-off 2.5im diameter

2. Six channel, laser in cavity, aerosol size analyser

3. Single wavelength nephelometer

4. Carbon soot concentration analyser

5. Automatic weather station

6. Shadow band sun photometer

The operation of the nephelometers and the sunphotometers will be controlled remotely (from Xanthi) and data will be collected in the same way. Three - dimensional air masses back trajectories will be supplied by the German Weather Service throughout the year. All filters will be analysed for major ions by ion chromatography and for major elements by atomic spectroscopy and XRF electron microprobe.

Key Scientists, Prof. S. Rapsomanikis, Post doctoral scientists

SUBCONTRACTOR C1 TO PARTNER C: Environmental Chemical Processes Laboratory, Division of Environmental and Analytical Chemistry, Dept. of Chemistry-University of Crete (ECPL-UC).

ECPL-UC will be involved in the determination of the atmospheric number concentration, mass loading, chemical composition, and optical characteristics of the aerosol. In addition it will help to assess the relation between these properties and the actinic flux measurements during the project. For this purposes the following measurements will be performed during the campaign:

Monitoring of Polycyclic Aromatic Hydrocarbons (PAHs) and petrogenic hydrocarbons (n-alkanes, UCM)

ECPL-UC will aslo provide information and statistics on the local aerosol conditions, especially for the planned campaign period

Equipment which will be used:

CGC/MS

Ion Chromatograph

Key Scientists, Dr. Euripides G. Stephanou, Professor: Principal Investigator, Dr. Nikolaos Mihalopoulos, Assistant Professor

PARTNER D: University of Oslo, Norway (UiO)

A 3-D CTM has been developed at the University of Oslo (UiO). This model has been developed to study tropospheric ozone distribution and changes (Berntsen et al., 1996; Berntsen and Isaksen, 1997; Jaffe et al., 1997). This model uses GCM generated wind fields (GISS) for 1 model year. The model has been run for several years with the full diurnal chemistry, reproducing global distributions of ozone NO_x and CO that are in agreement with observations of the latitudinal, longitudinal and seasonal distributions in the lower troposphere. There is however a tendency like in most CTMs to underestimate the concentrations in the upper troposphere, particularly the NO_x distribution (Jaffe et al., 1997). The chemical scheme is described in Berntsen and Isaksen (1997). The diurnal variation of approximately 50 chemical compounds is calculated with time steps of 20 minutes. Species in the oxygen, nitrogen, hydrcarbon (including CH₄ and CO) families are included. The 3-D CTM has the same chemistry as a 2-D model, which has been extensively used to study long term ozone variations in the troposphere, and which in particular has been used to show that UV flux increases from reduced stratospheric ozone have large scale implications for ozone and the oxidation capacity of the troposphere.

Recently a new version of the global 3-D CTM (Oslo CTM2) has been developed at the Department of Geophysics. This model will be the basic model for this study. In the troposphere where the model has been tested out it uses the same extensive chemical scheme as in the coarse resolution model (approximately 50 chemical compounds, calculation of full diurnal variations). The CTM2 uses wind velocity, subgrid processes, temperature, humidity and surface pressure data that have been extracted from the ECMWF model. The initial data from ECMWF is extracted on a resolution corresponding to T 63, and the CTM can be run on either T21, T42 or T63 resolution, corresponding to horizontal resolutions 5.6, 2.8 and 1.9 degrees respectively. The CTM is set up with the same vertical resolution as the (optional) 19-layers version of the ECMWF model.

A regional photochemical CTM with 50 km horizontal resolution, which is basically a tropospheric model with 20 vertical layers extending from the surface up to 100 hPa will also be used for short term studies (up to 1 month). Horizontally the model uses an extended EMEP grid, covering Europe, North Africa and most of the North Atlantic. Transport data and other physical parameters are taken from the HIRLAM regional model and updated every 6 hours. An extended chemical scheme for the tropospheric ozone chemistry has recently been implemented in the model, and the model has been run for one month with full diurnal chemistry. The ozone distribution and temporal variations for several locations in Europe has been compared with observations for the month of May 1992, and there are good agreements between observed and modeled distribution. Further comparisons of the regional distribution will be performed. This modeling work will be done in collaboration with The Norwegian Met. Office and Dr. Jan Jonson will be responsible for the work.

Key Scientists Professor Ivar Isaksen, Dr. Terje Berntsen,PhD student Jostein Sundet

Dr. Jan Eiof Jonson, Dr. Arve Kylling, In addition a programmer will participate in the project (WP 3, 4 months).

The major part of the work by the UiO group will be in WP3, but the group will also participate in WP 1 during the campaign and provide UV flux and photodissociation rate calculations, and photochemical model calculations as direct support for the campaign. The group will also participate in WP 2 in the analysis of the results.

ASSOCIATED PARTNER D1 TO PARTNER D: Ecole Polytecnique Federale de Lausanne, Switzerland (EPFL)

EPFL-LPAS will perform three-dimensional model calculations of episodes of several days from the PAUR-2 campaign. Base of the model will be a non-hydrostatic mesoscale prognostic Eulerian wind model, which is coupled online with sophisticated modules for the calculation of tropospheric chemistry and of the atmospheric radiation transfer, which includes the influence of aerosols. Massive parallelisation will be applied. The measurements of atmospheric trace constituents performed during the campaign will be used for model validation. The measurements of the actinic flux and the photolysis rates will serve to adjust the photolysis calculation within the model. Results from the regional model of Partner D (UiO) can be used for the boundary concentrations of the mesoscale domain. By applying the model to days with different conditions of atmospheric aerosols, which are expected during the campaign (maritime aerosol, Saharan dust, ...) the effects of the changing radiation on the chemistry of the troposphere will be investigated. Attention will be put also on the effect of tropospheric ozone on the radiation, which also will be measured.

During the time before the actual campaign the model will be prepared for the tasks. This includes the implementation of the domain (topography, land use, emission inventories), the development of an efficient computational method for the online calculation of photolysis rates under changing conditions, and the development of an interface for the nesting of the mesoscale model into the regional model of Partner D. In addition sensitivity studies on a box model basis will be performed in order to investigate possible effects. As soon as measurements from the PAUR-2 campaign are available the modeling of the actual episodes will start.

In addition the vertical fluxes of aerosols and ozone in the lower atmosphere will be measured by the LIDAR method in the PAUR 2 field campaign. Complementary information will be obtained with ground based meteo (wind speed and direction, total solar radiation, relative humidity, temperature, and pressure) as well as chemical detectors (NO_x, O₃). All measurements will be performed at one of the campaign sites, which has to be defined.

The range resolved information on the aerosol load as well as on the vertical ozone profile are very essential as input to the models participating in PAUR 2, in particular to the EPFL-LPAS model contribution. The EPFL-DIAL is equipped with two Nd:YAG lasers combined with Raman cells. The wavelengths at 289 nm and 299 nm are used to measure the differential absorption induced by the atmospheric ozone concentration, while the less absorbed wavelength at 299 nm is used as a probe of the vertical aerosol extinction coefficient. The LIDAR signals are collected on two seperate telescopes, one for the short range (50 m to 500 m) and a second for the long range (500 m to 5 km). The vertical resolution of the measurement is 15 m to 150 m and the averaging time is typically less than 3 min. Depending on visibility conditions the accuracy is 10 % to 20 %.

Key Scientists Dr. Bernd C. Krueger (Dipl. Chem.), Dr. Bertrand Calpini (Dipl. Phys.), Dr. Silvan Perego (Dipl. Chem.), Dr. Frank Kirchner (Dipl. Chem.), Dr. Philippe Quaglia (Dipl. Phys.), Dr. Valentin Simeonov (Dipl. Phys.), Gilles Larcheveque (PhD stud.) One postdoc

ASSOCIATED PARTNER D2 TO PARTNER D: Department of Environmental Studies, University of the Aegean (DESUA)

The role of the Department of Environmental Studies, University of the Aegean (DESUA) will be to use modeling and mathematical techniques to study the air history in the area of interest and to infer remote sources of important atmospheric pollutants. More precisely, DESUA contribution will focus on the following.

Use of a mesoscale numerical model (MIUU) to predict the 3-D wind fields and boundary layer processes relevant to the regional transport of atmospheric pollutants in the Mediterranean.

Calculation of air trajectories both in forward (source-oriented) as well as in backward (receptor-oriented) mode.

Provide a full meteorology report of the meteorological conditions and trajectories prevailed during the 45 day campaign

The dynamic model employed in the present project was developed at the meteorological Institute of Uppsala University (MIUU). The MIUU model is a three-dimensional mesoscale meteorological model that employs a higher-order turbulence closure scheme. It is designed for studies in the meso-g -scale, i.e. for spatial scales which are roughly in the interval 2-20 km. The model consists of prognostic equations for U and V components, liquid water, potential temperature, mixing ratio of total water, and turbulent kinetic energy, all transformed in a terrain influenced coordinate system. The prognostic equations are solved by using a third order scheme both in space and time for the advection terms. The diffusion terms are solved by a finite implicit scheme. Temperature at the surface is determined from the surface energy-balance equation. A prognostic equation involving the soil and other fluxes is used for predicting the soil temperature. The soil hydrology in the MIUU model is also made time-dependent with prognostic equations for the soil water content.

Key Scientists: Dr. Dimitrios Melas (Principal Investigator), M.Sc. Evagelos Goulis, M.Sc Eleni Voukloutzi

SUBCONTRACTOR D3 TO PARTNER D: Research Centre For Atmospheric Physics And Climatology, Academy Of Athens (ACATHEN), GREECE

The meteorological synoptic conditions and the air trajectories for the period during the experiment will be studied from the group of ACATHEN. The group will also participate in the interpretation of meteorological and air quality data collected during the campaign. Special emphasis will be given on the examination of the long-range transport of the Saharan aerosol, as well as the examination of the transport of tropospheric ozone of possible photochemical origin from northern areas. The rural concentrations of the other measured substances as well as the possible long average pollution levels according to the different wind sectors. The background concentrations of the pollutants will be estimated with the use of wind speed data. It should be noticed that few relevant data exist in the southern Mediterranean. The characteristics of the local photochemistry will be also studied by examining the diurnal variations of the pollutants.

Key Scientists Dr. C. Repapis, Director of the Research Centre

PARTNER E: University of Rome "La Sapienza", Italy, (URO)

The URO in collaboration with ENEA and CNR will be also be responsible for the following tasks of PAUR-II

Analysis of the effects of observed aerosols on the transfer of solar radiation in the troposphere and comparisons with observed UV irradiances will be carried out both in Rome and together with the PAUR II groups interested in such issue. Product of this analysis will be the definition of the UV modulation as a function of the aerosol (thin clouds) type and altitude.

Characterization of aerosols in terms of surface area and volume will be attempted. This analysis aims at defining bulk parameters of aerosols starting from single wavelength lidar observations and is pretty well established for stratospheric aerosols but less certain in the troposphere. Interaction with the groups computing airmass trajectories wiil provide a way to infer aerosols origin and, possibly, optical characteristics.

Combined analysis of ground and satellite observations. Aerosols and thin cloud observations from various satellite instruments (SAGE-2 and SAGE-3, GOME, AVHRR) will be acquired and analysed together with lidar observations. This work will aim both at the cross-validation of observations and at determining the horizontal extent of the aerosol layers observed at a fixed lidar point.

URO in collaboration with ENEA and CNR will be responsible for the measurements performed at the island of Lampedousa and also in Rome. These activities will include:

1. Brewer instrument. Brewer observations will be carried out continuously during the campaign. UV irradiance measurements between 290 and 360 nm (at 0.5 nm wavelength intervals) will be taken at solar zenith angle intervals of approximately 5(. Exact values of the observational angles will be agreed with the other PAUR-2 partners. Ozone and SO2 column measurements will be carried out between the UV measurements. The spectrophotometers will be calibrated for UV measurements before the campaign. Routine tests will be performed to guarantee the best performance during the campaign. The ozone and UV observations will be made available on a designed computer at the end of each day of measurements. Umkehr measurements will be carried out during the morning and evening periods and will be available on the computer site within 90 days from the end of the campaign.

2. Lidar. Aerosol lidar observations will be carried out every 3 hours between 8am and 12pm. Each lidar profile will consist of both aerosol and molecular cross sections ((a, (m) plus the backscatter ratio(R=1+((a /(m)) and, in the troposphere, the depolarization ratio. These variables will be provided ,with a height resolution of 30-150 m (depending on solar background noise), starting from 100m a.s.l. and up to approximately 40 km. Preliminary lidar profiles for the previous day will be posted each day on the computer site. Final analysis of lidar profiles will be completed and made available within 90 days from the end of the campaign. Lidar profiles will also be taken upon alert from the teams computing wind trajectories and/or coordinated with the groups in Crete.

Rome

Brewer observations will be taken in Rome providing total ozone, NO₂ and SO₂ values in the same fashion as in Lampedusa.

Key Scientist Prof. Giorgio Fiocco, Prof. Sabino Palmieri, D. Fua, M. Cacciani, one PhD student

ASSOCIATED PARTNER E1 TO PARTNER E: Ente per le Nuove tecnologie, l' Energia e l' Ambiente, Italy (ENEA)

The group of ENEA (AMB-GEM-CLIM, Activity "Observations and Measurements") operates the WMO Global Atmospheric Watch (GAW) station of Lampedusa. In 1992, in a collaboration between ENEA and the Italian National Research Council, measurements of concentration of greenhouse gases, on a weekly basis, started. During 1997, continuous measurements of CO₂ at Lampedusa should be activated. Concentrations of methane, N₂O, CFCs are also measured. The double Brewer to be deployed at Lampedusa is now at the ENEA centre of Casaccia.

Key Scientist Dr. Alcide di Sarra

ASSOCIATED PARTNER E2 TO PARTNER E: Italian Research Council (CNR) Frascati, Italy, (CNR)

Currently, four lidar receivers are operational: 1) a 6-mirror, middle-atmosphere Mie-Rayleigh system, 2) a 36-mirror, middle atmosphere Rayleigh system, 3) a single mirror stratospheric Mie receiver, and 4) a small lens receiver. The latter system became operational December 1996 and is capable of both troposphere and lower stratosphere aerosol observations, ranging from approximately 100m to 30km.. In early 1997 it will be provided with a depolarization channel for discrimination of spherical/non-spherical aerosols. In mid 1997 this microlidar will be moved from the laboratory into a trailer to allow for mobility of the system. The mobile lidar will be operational in the second half of 1997.

Key Scientists G.P. Gobbi, F. Congeduti, M. Viterbini, L. Reali

LAP-AUTH, C. Zerefos, Lab. of Atmospheric Physics, Physics Dept., Aristotle Univ. of Thessaloniki, 54 006 Thessaloniki, GREECE

Tel.: +30 31 998041 / 998156, ,Fax: +30 31 248602, zerefos@ccf.auth.gr

CNRS, J.P. Pommereau, Service d' Aeronomie du CNRS, BP3, 91371 Verrieres-Le-Buisson Cedex, FRANCE, Tel.: +33 1 64 47 4288 / 4386, Fax: +33 1 69 20 2999, pommereau@aerov.jussieu.fr

IASB, D. Gillotay, Instit. d' Aeronomie Spatiale de Belgique, Av. Circulaire 3, B-1180 Brussels, BELGIUM, Tel.: +32 2 373 0350, Fax: +32 2 374 8423, didier.gillotay@bira-iasb.oma.be

METCON, R. Schmitt, Meteorologie Consult GmbH, Auf der Platt 47, D-61479 Hessen

GERMANY, Tel.: +49 6174 61240, Fax: +49 6174 61436, METCON@compuserve.com

NTUA, A. Papayannis, Lasers & Applications Group, National Technical University of Athens, Heroon Polytechniou 9, 15780, GREECE, Tel.: +30 1 7722987, Fax: +30 1 7722928, apdlidar@central.ntua.gr

NCAR, S. Madronich, PO Box 3000, Boulder Co. 80307-3000, USA, Tel.: +1 303 497 1430, Fax: +1 303 497 1400, sasha@acd.ucar.edu

NOAA, J. Deluisi, Air Resources Laboratory , US Dept. of Commerce, 325 Broadway

Boulder, Co. 80303-3328, USA, Tel.: +1 303 497 6824, Fax: +1 303 497 6546, delouisi@srrb.noaa.gov

FMI, P. Taalas, Head, Section of O3 and UV Research, Vuorikatu 15A, PO Box 503

00101 Helsinki, FINLAND, Tel.: +358 9 1929 253, Fax: + 358 0 1929 563, petteri.taalas@fmi.fi

UMUN, P. Fabian, Bioklimatologie und Immissionsforschung der Universitat Munchen

Hohenbachrnstrabe 22, D-85254 Freising-Weihenstephan, GERMANY, Tel.: +49 81 61 71 47 40, Fax: +49 81 61 71 47 53, FABIAN@arbwiss.arwi.forst.uni-muenchen.de

DUTH, S. Rapsomanikis, Demokritus University of Thrace, Dept. of Environmental Engineering, 67100 Xanthi, GREECE, Tel.: +30 541 78980, Fax: +30 541 73488, rapso@demokritos.cc.duth.gr

ECPL-UC, E. Stefanou, Dept. of Chemistry, University of Crete, 71409 Herakleion

Crete, GREECE, Tel.: +30 81 322359, Fax: +30 81 393200, estef@cc.uch.gr

UiO, I. Isasken, University of Oslo, Dept. of Geophysics, 1022 Blindern, 0315 Oslo

NORWAY, Tel.: +47 22 85 58 22, Fax: +47 22 85 52 69, ivar.isaksen@geofysikk.uio.no

EPFL-LPAS, B. Krueger, Laboratoire de Pollution Atmospheric et Sol Laussanne CH-1015, SWITZERLAND, Tel.: +41 21 693 5701, Fax: +41 21 693 3626, bernd.krueger@dgr.epfl.ch

DESUA, D. Melas, University of the Aegean, Dept. of Environmental Studies, Karantoni Str. 17, 81100 Mytilene, Lesvos, GREECE, Tel.: +30 251 29187, Fax: +30 251 23783, melas@ccf.auth.gr

ACATHEN, C. Repapis, 3rd. Septemvriou 131, Academy of Athens, 11251 Athens, GREECE, Tel.: +30 1 8832048, Fax: +30 1 8832048

URO, G. Fiocco, University of Rome "La Sapienza", Dept. of Physics/G24/GMET, Piazzale A. Moro 2, 00185 Rome, ITALY, Tel.: +39 6 49913513, Fax: +39 6 49913522, Fiocco@g24ux.sci.uniromal.it

ENEA, A.G. di Sarra, Section "Global env. and climate", (AMB-GEM-CLIM), Activity of Obser. & Measurements, C.R. Casaccia, SP Anguillarese 301, S. Maria di Galeria , 00060 Roma, Lazio, ITALY, Tel.: +39 6 30484986/49913515, Fax: +39 6 30486678/49913522, disarra@eca700.casaccia.enea.it

CNR, G.P. Gobbi, Istituto di Fisica Dell' Atmosfera, Via G. Galilei - CP 27, 00044 Frascati