Anthropogenic emissions of NO_xover China: Reconciling the difference of inverse modeling results using GOME-2 and OMI measurements

Abstract

Inverse modeling using satellite observations of nitrogen dioxide (NO 2 ) columns has been extensively used to estimate nitrogen oxides (NO x ) emissions in China. Recently, the Global Ozone Monitoring Experiment-2 (GOME-2) and Ozone Monitoring Instrument (OMI) provide independent global NO 2 column measurements on a nearly daily basis at around 9:30 and 13:30 local time across the equator, respectively. Anthropogenic NO x emission estimates by applying previously developed monthly inversion (MI) or daily inversion (DI) methods to these two sets of measurements show substantial differences. We improve the DI method by conducting model simulation, satellite retrieval, and inverse modeling sequentially on a daily basis. After each inversion, we update anthropogenic NO x emissions in the model simulation with the newly obtained a posteriori results. Consequently, the inversion-optimized emissions are used to compute the a priori NO 2 profiles for satellite retrievals. As such, the a priori profiles used in satellite retrievals are now coupled to inverse modeling results. The improved procedure was applied to GOME-2 and OMI NO 2 measurements in 2011. The new daily retrieval-inversion (DRI) method estimates an average NO x emission of 6.9 Tg N/yr over China, and the difference between using GOME-2 and OMI measurements is 0.4 Tg N/yr, which is significantly smaller than the difference of 1.3 Tg N/yr using the previous DI method. Using the more consistent DRI inversion results, we find that anthropogenic NO x emissions tend to be higher in winter and summer than spring (and possibly fall) and the weekday-to-weekend emission ratio tends to increase with NO x emission in China.

Updated SO<sub>2</sub> emission estimates over China using OMI/Aura observations

“…The inversion methodology applied here is the one first presented in Martin et al (2003) and further applied in Martin et al (2006), Boersma et al (2008b), Lamsal et al (2010), Lin et al (2010), Gu et al (2014) and Zyrichidou et al (2015), among others. The main premise of the methodology resides in the mass balance equation (Leue et al, 2001) and requires three input parameters: the a priori emission field, E a (Sect.…”

“…The technique used here has recently been applied in both Europe (Zyrichidou et al, 2015) and China (Gu et al, 2014) for NO x emissions based on both GOME/ERS-2 (Global Ozone Monitoring Experiment/second European Remote Sensing satellite) and OMI/Aura observations. We aim to show how it can be applied also to SO 2 emissions and how the new top-down emissions compare against traditional bottom-up emission inventories.…”

Comparison of emissions inventories of anthropogenic air pollutants and greenhouse gases in China

“…The NO x emissions trend in Asia, and especially in China, has been an important topic, due to the rapid changes that have been observed in the past two decades (Richter et al, 2005;Gu et al, 2014). Figure 8 shows the seven regional NO x emissions estimated for each source sector.…”

Estimation of fossil-fuel CO<sub>2</sub> emissions using satellite measurements of "proxy" species

“…As a result, we obtain a "hybrid" FF CO 2 emission estimate integrating information coming from measurements and bottom-up inventories. The use of NO 2 and CO as proxy species in the context of our approach is justified because their satellite measurements are known to contain a strong signal associated with human activities in industrial regions and have abundantly been used earlier to constrain emissions of, respectively, NO x (e.g., Martin et al, 2003;Konovalov et al, 2006;Napelenok et al, 2008;Miyazaki et al, 2012;Gu et al, 2014) and CO (e.g., Arellano et al, 2004;Pétron et al, 2004;Kopacz et al, 2010;Hooghiemstra et al, 2012;Krol et al, 2013;Jiang et al, 2015) from various sources, including anthropogenic ones. Note that although NO x and CO emissions from FF burning are more sensitive to technological factors than CO 2 emissions, different aspects of the combustion technology are expected to affect NO x and CO emissions in different ways: e.g., while NO x emissions are strongly dependent on the temperature of combustion (more NO x is released at higher temperatures), CO emissions can be regarded as a measure of the incompleteness of combustion processes.…”