1. Atmospheric Composition Changes: causes and processes involved R. Zander Univ. Liège - Groupe Infrarouge de Physique Atmosphérique et Solaire (ULg-GIRPAS) and M. De Mazière Belgian Institute for Space Aeronomy (BIRA-IASB)

2. Context The atmosphere is changing: –Natural variations (solar variations, volcanic activity, …) –Anthropogenic changes (industrial, agricultural, traffic, …) To detect, understand and forecast the changes requires a long-term, integrated strategy including field observations (space and ground), modelling, and laboratory experiments (molecular spectroscopy, chemical reaction schemes and analysis techniques, …) The global dimension of the problem requires an internationally coordinated effort

3. How have the stratospheric Ozone layer and the UV radiation at the surface changed? Tools / expertise: –Belgian contributions to the international observing networks have expanded ; new instruments, observation and analysis techniques from space and ground have been developed –Advanced modelling and short-term forecasting techniques have become operational – example BASCOE –Additional 15 years of data (stratospheric gases, climate and source gases, aerosols, UV) have been submitted to international databases, supporting detection of changing trends –Dedicated laboratory techniques to determine molecular spectroscopic parameters Particular findings: –The gradual decrease of the stratospheric O 3 layer in the nineties was observed at all Belgian stations; at Uccle it amounts to -4% from 1982 to 2002 Jungfraujoch Uccle OHP Harestua Reunion Many more absorption lines of H 2 O have been observed in recent, high-quality laboratory spectra (upper frame) as compared to those archived in the latest HITRAN database release. Their accounting in radiative model calculations is an important contribution to help solving the so-called “Missing Absorber” problem.

4. How have the stratospheric Ozone layer and the UV radiation at the surface changed? (cont.) –The chlorine loading in the stratosphere was seen to stabilise around 1997, then to start decreasing; stratospheric BrO has continued to increase by 15% over the period 1994-2002 –In June 1991, the Mt Pinatubo volcano (Philippines) has erupted. The significant increase in aerosol loading on a global scale was observed from space. The consequent decrease of the abundances of O 3 and NO 2 was quantified at Jungfraujoch and in Uccle. –An anti-correlation between the amount of stratospheric O 3 and the UV irradiance at the surface has been confirmed at Uccle –The coupling ozone  climate needs further study; it makes the recovery of ozone uncertain at present. Policy support –Findings have been integrated in WMO assessments, thus supporting Montreal Protocol adjustments and Kyoto Protocol Time series of monthly mean total vertical column abundances of HCl and ClONO 2 derived from infrared solar observations at the Jungfraujoch from 1983 to 2002. Cly, which is the sum of the HCl and ClONO 2 columns is an excellent surrogate of the total inorganic chlorine loading in the stratosphere. The continuous lines represent the mean temporal trends of the various data sets. Bromine monoxide (BrO) is the most abundant inorganic bromine species during daylight, and therefore it is a good indicator of the total amount of inorganic bromine present in the stratosphere. Displayed here are the yearly averaged slant columns of BrO measured since 1994, as well as their associated uncertainties. A linear fit to the data (represented by the straight solid line) reveals an increase of about 15% of the stratospheric BrO content over the period 1994-2002. This increase is consistent with the recent years' reported rates of change of anthropogenic bromine source gases at the ground, as well as with recently published inorganic bromine measurements from stratospheric balloons (e.g., see WMO Report Nr. 47 [2003]). Percentage deviation of the total ozone column (measured with a Dobson spectrophotometer) at Uccle from the mean of the first ten years (1972-1982) of observations, showing that it has decreased by 4% during the past 2 decades. The data shown here have been corrected for the influence of SO 2 present in the boundary layer in the 1970s due to coal combustion.

5. Air quality and climate: How has tropospheric O 3 changed ? Tools / expertise –for evaluating impact of regulations and predicting future state of the troposphere: BELEUROS and IMAGES models Particular findings –Reductions of VOC emissions due to implementation of regulations like CAFE and CLRTAP have had a positive impact on the decrease of O 3 peak concentration events –Nevertheless background tropospheric O 3 is predicted to continue to increase in future (possibly by up to 60% until 2100), due to major increases in developing countries. This increase will have a positive forcing on climate. –for studying tropospheric photochemistry in the troposphere: laboratory experiments supporting kinetic and chemical mechanism calculations  implementation in models Visualisation of episodic peak ozone concentrations over Europe on August 6, 1997 at 12 hrs, as computed by the EUROS model, using emissions of 1997 without emission reductions (left) and with 50% reduction of NOx and VOC emissions in Europe compared to 1997 (right). The O 3 peak concentration is indicated according to the bottom colour scale (1  g/m 3 O 3 = 0.70 ppbv O 3 ). According to these model simulations, reductions of NOx and VOCs clearly have a positive impact on the tropospheric O 3 peak concentrations. The effect is confirmed by related observations.

6. Air quality and climate: Impact of particulate matter Tools/ expertise: -Field monitoring at various sites in the world -various laboratory techniques for determining the chemical and physical properties of aerosol components. Particular findings –Intensive studies of the composition and physical properties of aerosol in Belgium and elsewhere: Road traffic and biomass burning are the major origins of high levels of suspended particulate matter in the troposphere –Tropospheric and stratospheric aerosol impact climate; the contributions are highly uncertain still. –At most near-city, urban background and kerbsite sites, Belgium will not meet European standards for 2010 Aerosol mass concentrations at various sites in Europe, for aerosol particles of diameter < 10  m (PM10). The sites for which the data were provided by UGent are highlighted. The color code indicates different aerosol types: blue= natural background; green= rural background; yellow= near-city background; red= urban background; black= kerbside (i.e., along roads in cities). The data shown are the 5, 25, 50 (median), 75, and 95 % percentiles of 24-hour integrated PM10 mass concentrations, as well as their annual averages. The horizontal lines indicate target upper limit values to be achieved in the near-future.

7. Concluding remarks Belgium is strongly present on the international scene regarding Earth atmosphere research, incl. contributions to scientific programmation (scientific committees) and assessments at national and worldwide levels, in support of local, European and global environmental policies The Belgian public has been kept informed through the press, TV news, open public presentations, Web pages, etc. Services have been set up to issue warnings against high UV or alarming air pollution conditions. Continued research is needed to further monitor the evolution of the atmosphere, to better understand the links between the various components and scales in the atmosphere, to improve our forecasting ability, and to verify and further adjust environmental regulations and mitigation strategies.

8. Main contributors Belgian Institute for Space Aeronomy (BIRA-IASB) Royal Meteorological Institute of Belgium (KMI-IRM) KULeuven – Division for Physical and Analytical Chemistry Univ. Antwerpen – Laboratory of Biomolecular Mass Spectrometry and Micro and Trace Analysis Centre Univ. Gent – Institute for Nuclear Sciences Univ. Libre de Bruxelles - Unité de Spectroscopie de l’Atmosphère Univ. Liège - Groupe Infrarouge de Physique Atmosphérique et Solaire VITO - Remote Sensing and Atmospheric Processes