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A 14-month data setof MAX-DOAS (Multi-Axis Differential Optical Absorption Spectroscopy) tropospheric NO2 column observations inDe Bilt, the Netherlands, has been compared with the regional air qualitymodel Lotos-Euros. The model was run on a 7×7 km2 grid, the sameresolution as the emission inventory used. A study was performed to assessthe effect of clouds on the retrieval accuracy of the MAX-DOAS observations.Good agreement was found between modeled and measured troposphericNO2 columns, with an average difference of less than 1% of theaverage tropospheric column (14.5 · 1015 molec cm−2). Thecomparisons show little cloud cover dependence after cloud corrections forwhich ceilometer data were used. Hourly differences between observations andmodel show a Gaussian behavior with a standard deviation(σ) of 5.5 · 1015 molec cm−2. For daily averages oftropospheric NO2 columns, a correlation of 0.72 was found for allobservations, and 0.79 for cloud free conditions. The measured and modeledtropospheric NO2 columns have an almost identical distribution overthe wind direction. A significant difference between model and measurementswas found for the average weekly cycle, which shows a much stronger decreaseduring the weekend for the observations; for the diurnal cycle, the observedrange is about twice as large as the modeled range. The results of thecomparison demonstrate that averaged over a long time period, thetropospheric NO2 column observations are representative for a largespatial area despite the fact that they were obtained in an urban region.This makes the MAX-DOAS technique especially suitable for validation ofsatellite observations and air quality models in urban regions

MAX-DOAS tropospheric nitrogen dioxide column measurements compared with the Lotos-Euros air quality model