Recent reduction in NO _x emissions over China: synthesis of satellite observations and emission inventories

Abstract

Tropospheric nitrogen dioxide (NO 2 ) column densities detected from space are widely used to infer trends in terrestrial nitrogen oxide (NO x ) emissions. We study changes in NO 2 column densities using the Ozone Monitoring Instrument (OMI) over China from 2005 to 2015 and compare them with the bottom-up inventory to examine NO x emission trends and their driving forces. From OMI measurements we detect the peak of NO 2 column densities at a national level in the year 2011, with average NO 2 column densities deceasing by 32% from 2011 to 2015 and corresponding to a simultaneous decline of 21% in bottom-up emission estimates. A significant variation in the peak year of NO 2 column densities over regions is observed. Because of the reasonable agreement between the peak year of NO 2 columns and the start of deployment of denitration devices, we conclude that power plants are the primary contributor to the NO 2 decline, which is further supported by the emission reduction of 56% from the power sector in the bottom-up emission inventory associated with the penetration of selective catalytic reduction (SCR) increasing from 18% to 86% during 2011-2015. Meanwhile, regulations for vehicles also make a significant contribution to NO x emission reductions, in particular for a few urbanized regions (e.g., Beijing and Shanghai), where they implemented strict regulations for vehicle emissions years before the national schedule for SCR installations and thus reached their NO 2 peak 2-3 years ahead of the deployment of denitration devices for power plants.

Intercomparison of NO<sub><i>x</i></sub> emission inventories over East Asia

“…The peak year of the Chinese country-total emissions was 2011 in the EnKF and MEIC inventories, which is consistent with the results of Liu et al (2016). Irie et al (2016) showed that NO 2 column concentrations derived …”

The version 3 OMI NO<sub>2</sub> standard product

“…Satellite NO 2 data have been used as a proxy for (1) NO x emissions (van der A et al, 2017;Beirle et al, 2011;Boersma et al, 2015;Castellanos and Boersma, 2012;Curier et al, 2014;Ding et al, 2015;Duncan et al, 2014, de Foy et al, 2014Ghude et al, 2013;Jaeglé et al, 2004;Konovalov et al, 2006Konovalov et al, , 2010Lamsal et al, 2011;Liu et al, 2016;Lu et al, 2015;Lu and Streets, 2012;Martin et al, 2006;McLinden et al, 2016;Mijling and Van Der A, 2012;Richter et al, 2004Richter et al, , 2005Russell et al, 2012;Stavrakou et al, 2008;Streets et al, 2013;Vinken et al, 2014;Zhang et al, 2007;Zhou et al, 2012); (2) groundlevel NO 2 (Lamsal et al, 2008) and NO 2 deposition (Nowlan et al, 2014); and (3) emissions of co-emitted gases, including other pollutants, like particulate matter, and greenhouse gases, such as CO 2 (Berezin et al, 2013;Konovalov et al, 2016;Reuter et al, 2014).…”

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

“…Miyazaki et al (2017), van der A et al (2017), and Souri et al (2017) have further reported a recent decline in national NO x emissions on the basis of satellite data assimilation. Liu et al (2016b) have studied changes in NO 2 column densities for each province from 2005 to 2015 and have performed an intercomparison of a bottom-up inventory and satellite observations; the study attributes the decline in regional NO 2 to decreased emissions from power plants and urban vehicles. However, few analyses have been performed for individual cities or power plants, which are the primary targets of the new control measures.…”