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Abstract: Tropospheric NO2 column densities over China simulated with a regional model using different emission inventory input are compared with Global Ozone Monitoring Experiment (GOME) satellite data. These emission inventories include (i) emission estimates for the year 1995 from the Emission Database for Global Atmospheric Research (EDGAR), (ii) regional emission inventory used in the Transport and Chemical Evolution over the Pacific (TRACE-P) program with emission estimates for the year 2000 and (iii) national emission inventory used in the Chinese Ozone Research Programme (CORP) with emission estimates for the year 1995. Model simulations were performed for a summertime period and the results under clear-sky conditions were selected for comparison with GOME data of the years 1996 and 2000. The model generally reproduces high tropospheric NO2 column densities in polluted areas of China that have been observed by GOME. However, the model simulations do not agree with the GOME measurements in a quantitative sense for some regions. Region-to-region comparisons show that with all the emission inventories the model underestimates the tropospheric NO2 column density in remote and rural areas of China. It is found that TRACE-P underestimates the tropospheric NO2 column density in all the regions with respect to the GOME measurements (by more than 50%). CORP and EDGAR appear to behave well for the model simulations in the North of China (within 15% deviations), but poorer for the model simulations in other regions (within 30–80% deviations). Linear regressions were performed with the NO2 column densities available from GOME, Y, and the model, X, of each grid cell in selected regions. For all the region of China, comparison statistics are with and bias=−41% for EDGAR, with and bias=−67% for TRACE-P, and with and bias=−31% for CORP. [Copyright &y& Elsevier]

Abstract: Nitrogen dioxide (NO2) plays a key role in the chemistry of the atmosphere and is emitted mainly by combustion processes. These emissions have been increasing over India over the past few years due to rapid economic growth and yet there are very few systematic ground based observations of NO2 over this region. We thus take recourse to satellite data and compare tropospheric NO2 column abundances simulated by a chemical transport model, MOZART, with data from the Global Ozone Monitoring Experiment (GOME) for a few locations in India that have seen a rapid economic growth in the last decade. The model generally simulates higher columnar abundances of NO2 compared to GOME observations and does not reproduce the features of the observed seasonal behaviour. The combined uncertainties of the emission inventory and retrieval of the satellite data could be contributing factors to the discrepancies. It may be thus worthwhile to develop emission inventories for India at a higher resolution to include local level activity data. The ten year data (1996–2006) from GOME and SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY) show increasing trends for Indian cities where rapid industrial and vehicular traffic growth has been observed during this period. [Copyright &y& Elsevier]

Abstract: In this paper, the NOx emission scaling factors applied over the 2001 National Emissions Inventory (NEI) are estimated through a four-dimensional variational (4D-Var) approach using SCIAMACHY (Scanning Imaging Absorption spectroMeter for Atmospheric CHartographY) tropospheric NO2 columns measured during summer 2004. In the “top-down” approach, two-month average NO2 columns are assimilated into a regional chemical transport model (CTM), STEM, using different assimilation setups. In a basic setup, NOx emissions are adjusted by assimilating the NO2 columns. A more general setup of emission inversion allows the initial O3 concentrations be adjusted along with the NOx emissions. A final case is set up to assimilate both the NO2 columns and O3 measurement from various platforms while allowing adjustments of both the NOx emissions and the initial O3 concentrations. It is found that the addition of O3 measurements did not improve the NOx emission inversion. With the NOx emission at surface and upper levels being adjusted separately, results from four cases show that the elevated NOx emission reduction ranges from 8.9% to 11.4%, and the surface NOx emission reduction is up to 6.6%. All the cases show NOx emission reduction in Ohio valley and Washington, District of Columbia areas. [Copyright &y& Elsevier]

Abstract: A numerical analysis using a regional chemical transport model (CTM) is presented in comparison with Global Ozone Monitoring Experiment (GOME) and SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) satellite NO2 measurements over East Asia from 1996 to 2005 from a climatological perspective. Modeling results agree well with satellite retrievals in geographical distribution patterns, with systematic underestimation of the absolute values. The sharp increase in NO2 vertical column densities (VCDs) over central east China (CEC) after the year 2000 (14.1–20.5%yr−1 for the satellite observations and 10.8%yr−1 for model simulations) is analyzed quantitatively over different megacity clusters. The distinct emission increase patterns are responsible for the different increase trends observed over the Beijing megacity cluster (BJ), the Yangtze Delta (YD) and other CEC regions. The growth rate of satellite measured and CMAQ-modeled NO2 VCDs for the YD is much higher than that in other regions, with no clear seasonal variation. Apart from BJ and YD, NO2 emissions from other regions in CEC also expand considerably. [Copyright &y& Elsevier]

The distribution and budget of tropospheric NOx over Asia, especially India, are examined using the global 3D chemistry–meteorology model MATCH-MPIC and GOME NO2 columns. Enhanced abundances of NO2 over China and northeast India are reproduced by the model, as are the pronounced maxima during biomass burning periods, though somewhat underestimated. The mean NO2 column over India is also reproduced, though the model has trouble with the seasonal cycle for unknown reasons. Model sensitivity tests for the Indian region indicate that the scaled sensitivity to changes in the local NOx source is 60–70% for lower tropospheric NOx and is only 10–25% for tropospheric O3, indicating that moderate reductions or increases in current NOx emissions are not expected to lead to large changes in regional O3 levels. In the upper troposphere, during winter nearly all of the NOx comes from remote sources, while in summer deep convection causes the upper troposphere to become sensitive to local surface emissions (∼40–50% scaled sensitivity) and lightning NOx production (∼10–20%). The regional lifetime of NOx estimated for India, based on MATCH output is about 15–23 h, comparable to the lifetime of NOx over China (14–21 h), while over Indonesia (23–43 h) and North Asia (21–47 h), it is longer and highly seasonal. Implications of these results are discussed. [Copyright &y& Elsevier]