An inversion of NOx and non-methane volatile organic compound (NMVOC) emissions using satellite observations during the KORUS-AQ campaign and implications for surface ozone over East Asia

The prior amount of total NOx emissions is mainly dictated by values reported in the MIX-Asia 2010 inventory. After the inversion we conclude that there is a decline in emissions (before, after, change) for China (87.94 +/- 44.09 Gg d(-1), 68.00 +/- 15.94 Gg d(-1), -23 %), North China Plain (NCP) (27.96 +/- 13.49 Gg d(-1), 19.05 +/- 2.50 Gg d(-1), -32 %), Pearl River Delta (PRD) (4.23 +/- 1.78 Gg d(-1), 2.70 +/- 0.32 Gg d(-1), -36 %), Yangtze River Delta (YRD) (9.84 +/- 4.68 Gg d(-1), 5.77 +/- 0.51 Gg d(-1), -41 %), Taiwan (1.26 +/- 0.57 Gg d(-1), 0.97 +/- 0.33 Gg d(-1), -23 %), and Malaysia (2.89 +/- 2.77 Gg d(-1), 2.25 +/- 1.34 Gg d(-1), -22 %), all of which have effectively implemented various stringent regulations.

In contrast, South Korea (2.71 +/- 1.34 Gg d(-1), 2.95 +/- 0.58 Gg d(-1), +9 %) and Japan (3.53 +/- 1.71 Gg d(-1), 3.96 +/- 1.04 Gg d(-1), +12 %) are experiencing an increase in NOx emissions, potentially due to an increased number of diesel vehicles and new thermal power plants. We revisit the well-documented positive bias (by a factor of 2 to 3) of MEGAN v2.1 (Model of Emissions of Gases and Aerosols from Nature) in terms of biogenic VOC emissions in the tropics.

The inversion, however, suggests a larger growth of VOCs (mainly anthropogenic) over NCP (25 %) than previously reported (6 %) relative to 2010. The spatial variation in both the magnitude and sign of NOx and VOC emissions results in nonlinear responses of ozone production and loss. Due to a simultaneous decrease and increase in NOx/VOC over NCP and YRD, we observe a similar to 53% reduction in the ratio of the chemical loss of NOx (LNOx) to the chemical loss of ROx (RO2 + HO2) over the surface transitioning toward NOx-sensitive regimes, which in turn reduces and increases the afternoon chemical loss and production of ozone through NO2 + OH (-0.42 ppbv h(-1))/HO2 (and RO2)+NO (+0.31 ppbv h(-1)).