Construction of Satellite Derived PM2.5 Maps using the Relationship between AOD and PM2.5 at the Cabauw Experimental Site for Atmospheric Research (CESAR) - The Netherlands

To acquire daily estimates of PM2.5 distributions based on satellite data one depends critically on a well 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 mug/ m3, which confirms that the Netherlands are characterized 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 R
²
=0.6 for situations with fair weather. This indicates that AOD data contain information about the temporal evolution of PM2.5. We 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 mug/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 for the first time based on MODIS data only.