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. We developed a top-down methodology combining the inversed chemistrytransport modeling and satellite-derived tropospheric vertical column ofNO2 and estimated the NOx emissions of the Yangtze River Delta (YRD)region at a horizontal resolution of 9 km for January, April, July, andOctober 2016. The effect of the top-down emission estimation on air qualitymodeling and the response of ambient ozone (O3) and inorganic aerosols(SO42-, NO3-, and NH4+, SNA) to the changedprecursor emissions were evaluated with the Community Multi-scale AirQuality (CMAQ) system. The top-down estimates of NOx emissions weresmaller than those (i.e., thebottom-up estimates) in a national emission inventory, Multi-resolution Emission Inventory for China (MEIC), for all the 4 months, and the monthly mean wascalculated to be 260.0 Gg/month, 24 % less than the bottom-up one. TheNO2 concentrations simulated with the bottom-up estimate of NOxemissions were clearly higher than the ground observations, indicating thepossible overestimation in the current emission inventory, attributed to itsinsufficient consideration of recent emission control in the region. Themodel performance based on top-down estimate was much better, and thebiggest change was found for July, with the normalized mean bias (NMB) andnormalized mean error (NME) reduced from 111 % to −0.4 % and from111 % to 33 %, respectively. The results demonstrate the improvement ofNOx emission estimation with the nonlinear inversed modeling andsatellite observation constraint. With the smaller NOx emissions in thetop-down estimate than the bottom-up one, the elevated concentrations ofambient O3 were simulated for most of the YRD, and they were closer toobservations except for July, implying the VOC (volatile organiccompound)-limited regime of O3 formation. With available groundobservations of SNA in the YRD, moreover, better model performance ofNO3- and NH4+ was achieved for most seasons, implyingthe effectiveness of precursor emission estimation on the simulation ofsecondary inorganic aerosols. Through the sensitivity analysis of O3formation for April 2016, the decreased O3 concentrations were foundfor most of the YRD region when only VOC emissions were reduced or the reducedrate of VOC emissions was 2 times of that of NOx, implying thecrucial role of VOC control in O3 pollution abatement. The SNA levelfor January 2016 was simulated to decline 12 % when 30 % of NH3emissions were reduced, while the change was much smaller with the samereduced rate for SO2 or NOx. The result suggests that reducingNH3 emissions was the most effective way to alleviate SNA pollution of theYRD in winter.

atmospheric chemistry and physics

Improvement of the satellite-derived NO&amp;lt;sub&amp;gt;&amp;lt;i&amp;gt;x&amp;lt;/i&amp;gt;&amp;lt;/sub&amp;gt; emissions on air quality modeling and its effect on ozone and secondary inorganic aerosol formation in the Yangtze River Delta, China