Inverse estimation of NO_x emissions over China and India 2005–2016: contrasting recent trends and future perspectives

Abstract

Bottom-up emission inventories can provide valuable information for understanding emission status and are needed as input datasets to drive chemical transport models. However, this type of inventory has the disadvantage of taking several years to be compiled because it relies on a statistical dataset. Top-down approaches use satellite data as a constraint and overcome this disadvantage. We have developed an immediate inversion system to estimate anthropogenic NO x emissions with NO 2 column density constrained by satellite observations. The proposed method allows quick emission updates and considers model and observation errors by applying linear unbiased optimum estimations. We used this inversion system to estimate the variation of anthropogenic NO x emissions from China and India from 2005 to 2016. On the one hand, NO x emissions from China increased, reaching a peak in 2011 with 29.5 Tg yr −1 , and subsequently decreased to 25.2 Tg yr −1 in 2016. On the other hand, NO x emissions from India showed a continuous increase from 2005 to 2016, reaching 13.9 Tg yr −1 in 2016. These opposing trends from 2011 to 2016 were −0.83 and +0.76 Tg yr −1 over China and India, respectively, and correspond to strictly regulated and unregulated future scenarios. Assuming these trends continue after 2016, we expect NO x emissions from China and India will be similar in 2023, with India becoming the world's largest NO x emissions source in 2024.

Rapid reduction of black carbon emissions from China: evidence from 2009–2019 observations on Fukue Island, Japan

“…watched in future, to assess its impact on BC transport to higher latitudes and/or snow albedo change. Itahashi et al (2019) recently found that NO x emission from NE China exhibited a later peak between 2013 and 2016, consistent to the tendency for BC. Region II (N-CEC) showed a CO decrease but only a very weak BC decrease, suggesting that the BC/CO emission ratio increased.…”

“…Importantly, the balance or lag between SO 2 and BC reductions could have strong climate effects. Using satellite data inversion, emission reductions from China were estimated to be 24-33%, or (2.4-3.3)% y −1 for SO 2 during 2007-2016 (Qu et al, 2019) and (3.0-5.4)% y −1 for NO x during 2011-2016 (Itahashi et al, 2019). Our estimated BC emission reductions of 4.6% y −1 were nearly equal to or even faster than these rates.…”

Rapid reduction in black carbon emissions from China: evidence from 2009–2019 observations on Fukue Island, Japan

“…For the MAAP, measurements of reflectance at two angles, in addition to transmittance, were made with respect to the particleladen filter, and the built-in algorithm for radiative transfer enabled the separation of scattering from absorption (Petzold and Schönlinner, 2004). We demonstrated that the two instruments had a high level of agreement and compatibility at Fukue Island once the mass absorption cross section for the MAAP was modified from manufacturer's recommendation of (6.6) to 10.3 m 2 g −1 (Kanaya et al, 2013(Kanaya et al, , 2016. The filter-based observations were also successfully compared to an ECOC analyzer (Sunset Laboratory Inc., Tigard, Oregon, USA) in which BC was calibrated as CO 2 after combustion and to a Single Particle Soot Photometer (SP2; Droplet Measurement Technologies, Longmont, Colorado, USA) in which Alfa Aesar™ Fullerene soot (Fisher Scientific, part of Thermo Fisher Scientific, Leicestershire, England) particles with a known mass were used as a calibration standard (Miyakawa et al, 2017).…”

“…In this context, long-term observations, which are based on reliable instruments with careful calibration, are desired to determine the BC emissions trends in China. We have been conducting such observations of BC and related species at Fukue Island since 2009 (Kanaya et al, 2013(Kanaya et al, , 2016Miyakawa et al, 2017). This site receives air masses from various latitudinal bands in China during the winter monsoon (effective from autumn to spring) with negligible effects from local sources.…”

“…This site receives air masses from various latitudinal bands in China during the winter monsoon (effective from autumn to spring) with negligible effects from local sources. It is unique that two instruments (a continuous soot monitoring system -COSMOS; a Multi-Angle Absorption Photometer -MAAP) are regularly operated in parallel, that their compatibility is assured, and that comparisons with other BC-measuring instruments have been successfully made on-site (i.e., with a Single Particle Soot Photometer (SP2) and an elemental carbon and organic carbon (ECOC) analyzer; Miyakawa et al, 2017;Kanaya et al, 2013). Since the major source region is located some distance (ca.…”