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. We used the GEOS-Chem model and its adjoint to quantify Chinese non-methanevolatile organic compound (NMVOC) emissions for the year 2007, using thetropospheric column concentrations of formaldehyde and glyoxal observed bythe Global Ozone Monitoring Experiment 2A (GOME-2A) instrument and the OzoneMonitoring Instrument (OMI) as quantitative constraints. We conducted aseries of inversion experiments using different combinations of satelliteobservations to explore their impacts on the top-down emission estimates. Ourtop-down estimates for Chinese annual total NMVOC emissions were 30.7 to 49.5(average 41.9) Tg yr−1, including 16.4 to 23.6 (average 20.2)Tg yr−1 from anthropogenic sources, 12.2 to 22.8 (average 19.2)Tg yr−1 from biogenic sources, and 2.08 to 3.13 (average 2.48)Tg yr−1 from biomass burning. In comparison, the a priori estimatefor Chinese annual total NMVOC emissions was 38.3 Tg yr−1, including18.8 Tg yr−1 from anthropogenic sources, 17.3 Tg yr−1 frombiogenic sources, and 2.27 Tg yr−1 from biomass burning. Thesimultaneous use of glyoxal and formaldehyde observations helped distinguishthe NMVOC species from different sources and was essential in constraininganthropogenic emissions. Our four inversion experiments consistently showedthat the Chinese anthropogenic emissions of NMVOC precursors of glyoxal werelarger than the a priori estimates. Our top-down estimates for Chineseannual emission of anthropogenic aromatics (benzene, toluene, and xylene)ranged from 5.5 to 7.9 Tg yr−1, 2 % to 46 % larger than theestimate of the a priori emission inventory (5.4 Tg yr−1). Three outof our four inversion experiments indicated that the seasonal variation inChinese NMVOC emissions was significantly stronger than indicated in the apriori inventory. Model simulations driven by the average of our top-downNMVOC emission estimates (which had a stronger seasonal variation than the apriori) showed that surface afternoon ozone concentrations over easternChina increased by 1–8 ppb in June and decreased by 1–10 ppb in Decemberrelative to the simulations using the a priori emissions and were in betteragreement with measurements. We concluded that the satellite observations offormaldehyde and glyoxal together provided quantitative constraints on theemissions and source types of NMVOCs over China and improved ourunderstanding on regional chemistry.

Adjoint inversion of Chinese non-methane volatile organic compound emissions using space-based observations of formaldehyde and glyoxal