Abstract. To acquire daily estimates of PM2.5 distributions based on satellite data one depends critically on an established relation between AOD and ground level PM2.5. In this study we aimed to experimentally establish the AOD-PM2.5 relationship for the Netherlands. For that purpose an experiment was set-up at the AERONET site Cabauw. The average PM2.5 concentration during this ten month study was 18 μg/m3, which confirms that the Netherlands are characterised by a high PM burden. A first inspection of the AERONET level 1.5 (L1.5) AOD and PM2.5 data at Cabauw showed a low correlation between the two properties. However, after screening for cloud contamination in the AERONET L1.5 data, the correlation improved substantially. When also constraining the dataset to data points acquired around noon, the correlation between AOD and PM2.5 amounted to R2=0.6 for situations with fair weather. This indicates that AOD data contain information about the temporal evolution of PM2.5. We had used LIDAR observations to detect residual cloud contamination in the AERONET L1.5 data. Comparison of our cloud-screed L1.5 with AERONET L2 data that became available near the end of the study showed favorable agreement. The final relation found for Cabauw is PM2.5=124.5*AOD–0.34 (with PM2.5 in μg/m3) and is valid for fair weather conditions. The relationship determined between MODIS AOD and ground level PM2.5 at Cabauw is very similar to that based on the much larger dataset from the sun photometer data, after correcting for a systematic overestimation of the MODIS data of 0.05. We applied the relationship to a MODIS composite map to assess the PM2.5 distribution over the Netherlands. Spatial dependent systematic errors in the MODIS AOD, probably related to variability in surface reflectance, hamper a meaningful analysis of the spatial distribution of PM2.5 using AOD data at the scale of the Netherlands.

Abstract. Biodiversity is strongly affected by the deposition of nitrogen and sulfur on terrestrial ecosystems. In this paper

Nature of the problem Reactive nitrogen (N • r) is of fundamental importance in biological and chemical processes in the atmosphere-biosphere system, altering the Earth's climate balance in many ways. Th ese include the direct and indirect emissions of nitrous oxide (N 2 O), atmospheric N r deposition and tropospheric ozone formation (O 3), both of which alter the biospheric CO 2 sink, N r supply eff ects on CH 4 emissions, and the formation of secondary atmospheric aerosols resulting from the emissions of nitrogen oxides (NO x) and ammonia (NH 3). Human production and release of N • r into the environment is thus expected to have been an important driver of European greenhouse balance. Until now, no assessment has been made of how much of an eff ect European N r emissions are having on net warming or cooling. Approaches Th is chapter summarizes current knowledge of the role of N • r for global warming. Particular attention is given to the consequences of atmospheric N r emissions. Th e chapter draws on inventory data and review of the literature to assess the contribution of anthropogenic atmospheric N r emissons to the overall change in radiative forcing (between 1750 and 2005) that can be attributed to activities in Europe. Th e use of N • r fertilizers has major additional eff ects on climate balance by allowing increased crop and feed production and larger populations of livestock and humans, but these indirect eff ects are not assessed here. Key fi ndings/state of knowledge Due to its multiple, complex eff ects on biospheric and atmospheric processes, the importance of N • r for the European greenhouse gas balance has so far received insuffi cient attention. Th e main warming eff ects of European anthropogenic N • r emissions are estimated to be from N 2 O (17 (15-19) mW/m 2) and from the reduction in the biospheric CO 2 sink by tropospheric O 3 (4.4 (2.3-6.6) mW/m 2). Th e main cooling eff ects are estimated to be from increasing the biospheric CO 2 sink by atmospheric N r deposition at −19 (−30 to −8) mW/m 2 and by light scattering eff ects of N r containing aerosol (−16.5 (−27.5 to −5.5) mW/m 2), in both cases resulting from emissions of NO x and NH 3. Th e production of O • 3 from European emissions of NO x is estimated to have a modest warming eff ect (2.9 (0.3-5.5) mW/m 2), which is largely off set by the cooling eff ect of O 3 in reducing the atmospheric lifetime of CH 4 (−4.6 (−6.7 to −2.4) mW/m 2), giving an uncertain net warming of +1.7 (−6.4 to +3.1) mW/m 2). Overall, including all of these terms, European N • r emissions are estimated to have a net cooling eff ect, with the uncertainty bounds ranging from a substantial cooling eff ect to a small warming eff ect (−15.7 (−46.7 to +15.4) mW/m 2). Major uncertainties/challenges Th e largest uncertainties concern the aerosol and N • r fertilization eff ects, and the estimation of the European contributions within the global context. Published estimates suggest that the default N • 2 O emission factor of 1% used by IPCC for indirect emissions from soi...

A large shortcoming of current chemistry transport models for simulating the fate of ammonia in the atmosphere is the lack of a description of the bi-directional surface-atmosphere exchange. In this paper, results of an update of the dry deposition module DEPAC in the LOTOS-EUROS model are discussed. It is shown that with the new description, which includes bi-directional surface-atmosphere exchange, the modeled ammonia concentrations increase almost everywhere, in particular in agricultural source areas. The reason is that by using a compensation point the ammonia life time and transport distance is increased. As a consequence, deposition of ammonia and ammonium decreases in agricultural source areas, while it increases in large nature areas and remote regions especially in Southern Scandinavia. The inclusion of a compensation point for water reduces the dry deposition over sea and allows reproducing the observed marine background concentrations at coastal locations to a better extend. A comparison with measurements shows that the model results better represent the measured ammonia concentrations. The concentrations in nature areas are slightly overestimated, while the concentrations in agricultural source areas are still underestimated. Although the introduction of the compensation point improves the model performance, the modeling of ammonia remains challenging. Important aspects are emission patterns in space and time as well as a proper approach to deal with the high concentration gradients in relation to model resolution. In short, the inclusion of a bi-directional surface atmosphere exchange is a significant step forward for modeling ammonia

To design effective mitigation strategies the origin of air pollutants needs to be known. Chemistry transport models can be used to assess the origin of air pollution across a large domain. However, in traditional simulations the information on origin is lost and brute force scenario studies are performed to assess the origin. Alternatively, one can trace the origin of air pollutants throughout a simulation using a labeling approach. In this paper we document and demonstrate a newly developed labeling module for the chemistry transport model LOTOS-EUROS which tracks the source allocation for all particulate matter components and precursor gases. Dedicated simulations confirmed that the new module functions correctly. The new module provides more accurate information about the source contributions than using a brute force approach with scenario runs as the chemical regime remains unchanged. An important advantage of the new module is the reduction of computation costs and analysis work associated with the calculations. The new module was applied to assess the origin of particulate nitrate across the Netherlands. Averaged across the Dutch territory the main contributions to nitrate derive from road and non-road transport as well as power plants. Overall, only one-fifth of the concentration derived from sources located inside the country. The new technology enables new research directions as improved information on pollution origin is desired for policy support as well as scientific applications