Global tropospheric NO₂ column distributions: Comparing three‐dimensional model calculations with GOME measurements

Abstract

Abstract. Tropospheric NO2 columns derived from the data products of the Global Ozone Monitoring Experiment (GOME), deployed on the ESA ERS-2 satellite, have been compared with model calculations from two global three-dimensional chemistry transport models, IMAGES and MOZART. The main objectives of the study are an analysis of the tropospheric NO2 data derived from satellite measurements, an interpretation of it and evaluation of its quality using global models, and an estimation the role of NO2 in radiative forcing. The measured and modeled NO2 columns show similar spatial and seasonal patterns, with large tropospheric column amounts over industrialized areas and small column amounts over remote areas. The comparison of the absolute values of the measured and modeled tropospheric column amounts are particularly dependent upon uncertainties in the derivation of the tropospheric NO2 columns from GOME and the difficulty of modeling the boundary layer in global models, both of which are discussed below. The measured tropospheric column amounts derived from GOME data are of the same order as those calculated by the MOZART model over the industrialized areas of the United States and Europe, but a factor of 2-3 larger for Asia. The modeled tropospheric NO2 columns from MOZART as well as the column amounts measured by GOME are in good agreement with NO2 columns derived from observed NO2 mixing ratios in the boundary layer in eastern North America. The comparison of the models to the GOME data illustrates the degree to which present models reproduce the hot spots seen in the GOME data.

Rapid intercontinental air pollution transport associated with a meteorological bomb

“…Since no correction is applied for thin clouds that may have been present in the GOME pixels, the amount of NO 2 is probably underestimated, as detailed in Velders et al (2001) and Richter and Burrows (2002). Even a cloud fraction of 10% can lead to an underestimation of up to 100% in the GOME measurements if the cloud is above the NO 2 layer, or an overestimation of 50% if it is below the layer.…”

“…This approach is based on the assumptions that a) stratospheric NO 2 does not depend on longitude, and that b) the reference region has a negligible tropospheric NO 2 burden. Tropospheric NO 2 columns from GOME have been validated against independent measurements (Heland et al, 2002), and have been extensively compared to model results (Velders et al 2001;Lauer et al 2002;Martin et al 2002).…”

Tropospheric NO<sub>2</sub> columns: a comparison between model and retrieved data from GOME measurements

“…Although direct absorption of ultraviolet and visible radiation by tropospheric NO 2 is not thought to provide a large atmospheric forcing, local maxima of up to 0.1 to 0.15 Wm −2 can be reached (Velders et al, 2001). As tropospheric O 3 is also a significant greenhouse gas, NO 2 also contributes indirectly to radiative forcing.…”

“…Stratospheric NO 2 is not included in the airmass factor calculation as the tropospheric slant columns have already been corrected for the stratospheric contribution, and the influence of stratospheric NO 2 on the radiative transfer can be neglected. Velders et al, 2001). A brief summary of the assumptions for derivation of the tropospheric NO 2 column amounts from the GOME measurements is given by Table 1.…”

“…Lauer et al: Tropospheric NO 2 columns al. (2001) and Velders et al (2001), climatological averages of the tropospheric NO 2 columns retrieved from GOME have been used. These have been compared with those obtained from the interactively coupled chemistry-climate model ECHAM4.L39(DLR)/CHEM on global and regional scales.…”