NO<sub><i>x</i></sub> emission trends over Chinese cities estimated from OMI observations during 2005 to 2015

Abstract

Abstract. Satellite nitrogen dioxide (NO2) observations have been widely used to evaluate emission changes. To determine trends in nitrogen oxides (NOx) emission over China, we used a method independent of chemical transport models to quantify the NOx emissions from 48 cities and seven power plants over China, on the basis of Ozone Monitoring Instrument (OMI) NO2 observations from 2005 to 2015. We found that NOx emissions over 48 Chinese cities increased by 52 % from 2005 to 2011 and decreased by 21 % from 2011 to 2015. The decrease since 2011 could be mainly attributed to emission control measures in power sector; while cities with different dominant emission sources (i.e., power, industrial, and transportation sectors) showed variable emission decline timelines that corresponded to the schedules for emission control in different sectors. The time series of the derived NOx emissions was consistent with the bottom-up emission inventories for all power plants (r = 0. 8 on average), but not for some cities (r = 0. 4 on average). The lack of consistency observed for cities was most probably due to the high uncertainty of bottom-up urban emissions used in this study, which were derived from downscaling the regional-based emission data to city level by using spatial distribution proxies.

The Ozone Monitoring Instrument: overview of 14 years in space

“…This section highlights the use of the long OMI data record for better understanding trends in pollutants including SO 2 and NO 2 particularly in China (e.g., Wang et al, 2012;Ling et al, 2017;Liu et al, 2016aLiu et al, , 2017Zhang et al, 2017) and India (David and Nair, 2013;Ghosh et al, 2017), as well as for aerosol presence using the OMI aerosol index. OMI's data have been used to infer substantial trends that have occurred in SO 2 and NO 2 pollution around the world over the last decade (e.g., Duncan et al, 2016;Krotkov et al, 2016).…”

MAX-DOAS NO<sub>2</sub> observations over Guangzhou, China; ground-based and satellite comparisons

“…Although a rapid growth in NO x emissions has been observed over China by satellite sensors during the previous two decades (Zhang et al, 2007;Liu et al, 2017), a sharp decline is evident in recent years van der A et al, 2017). Satellite observations constitute an important tool of investigating the air pollution levels and trends in global (e.g., Velders et al, 2001;Schneider and van der A, 2012) and regional (e.g., Zyrichidou et al, 2009;Hilbol et al, 2013) scales.…”

Reconciling the differences between OMI-based and EPA AQS in situ NO<sub>2</sub> trends

“…REAM updates most of the meteorology inputs every 30 minutes while those related to convective transport and lightning parameterization are updated every 5 minutes. The chemistry mechanism expands that of a global CTM GEOS-Chem (V9-02) with aromatics chemistry (Bey et al, 2001;Liu et al, 2010Liu et al, , 2012aLiu et al, , 2012bZhang et al, 2017). For consistency, the GEOS-Chem (V9-02) simulation with 2°× 2.5° resolution is used to generate initial and 30 boundary conditions for chemical tracers.…”

“…For recent model evaluations of REAM with observations, we refer readers to Zhang et al (2016aZhang et al ( , 2016b, Cheng et al (2017), and Zhang et al (2017).…”

“…For trend analysis, the tropospheric NO2 products from OMI surpass the others for a relatively high spatial resolution and over one decade of continuous operation (Boersma et al, 2004;Boersma et al, 2011). Thus, OMI NO2 retrievals are widely applied in NO2 and NOx emission trend studies (e.g., Lin et al, 2010Lin et al, , 2011Castellanos et al, 2012;Russell et al, 2012;Gu et al, 2013;Lamsal et al, 2015;Lu et al, 2015;Tong 15 et al, 2015;Cui et al, 2016;Duncan et al, 2016;de Foy et al, 2016ade Foy et al, , 2016bKrotkov et al, 2016;Liu et al, 2017). reported that the reduction rates calculated from OMI NO2 VCDs and AQS surface NO2 data at eight cities were -35% and -38% from 2005 to 2012, respectively.…”