Carbonaceous aerosols in China: top-down constraints on primary sources and estimation of secondary contribution

Abstract

We simulate elemental carbon (EC) and organic carbon (OC) aerosols in China and compare model results to surface measurements at Chinese rural and background sites, with the goal of deriving "top-down" emission estimates of EC and OC, as well as better quantifying the secondary sources of OC. We include in the model state-of-the-science Chinese "bottom-up" emission inventories for EC (1.92 Tg C yr<sup>−1</sup>) and OC (3.95 Tg C yr<sup>−1</sup>), as well as updated secondary OC formation pathways. The average simulated annual mean EC concentration at rural and background site is 1.1 μg C m<sup>−3</sup>, 56% lower than the observed 2.5 μg C m<sup>−3</sup>. The average simulated annual mean OC concentration at rural and background sites is 3.4 μg C m<sup>−3</sup>, 76% lower than the observed 14 μg C m<sup>−3</sup>. Multiple regression to fit surface monthly mean EC observations at rural and background sites yields best estimate of Chinese EC source of 3.05 ± 0.78 Tg C yr<sup>−1</sup>. Based on the top-down EC emission estimate and observed seasonal primary OC/EC ratios, we estimate Chinese OC total emissions to be 6.67 ± 1.30 Tg C yr<sup>−1</sup>. Using these top-down estimates, the simulated average annual mean EC concentration at rural and background sites significantly improved to 1.9 μg C m<sup>−3</sup>. However, the model still significantly underestimates observed OC in all seasons (simulated average annual mean OC at rural and background sites is 5.4 μg C m<sup>−3</sup>), with little skill in capturing the spatiotemporal variability. Secondary formation accounts for 21% of Chinese annual mean surface OC in the model, with isoprene being the most important precursor. In summer, as high as 62% of the observed surface OC may be due to secondary formation in eastern China. Our analysis points to three shortcomings in the current bottom-up inventories of Chinese carbonaceous aerosols: (1) the anthropogenic source is severely underestimated, particularly for OC; (2) there is a missing source in western China, likely associated with the use of biofuels or other low-quality fuels for heating; and (3) sources in fall are not well represented, either because the seasonal shifting of emissions and/or secondary formation are poorly captured or because specific fall emission events are missing. More regional measurements with better spatiotemporal coverage are needed to resolve these shortcomings

Top‐down estimate of China's black carbon emissions using surface observations: Sensitivity to observation representativeness and transport model error

“…Other regions not represented by the sites are denoted as the Other Regions of China (ORC). Compared with previous top-down studies which did not distinguish subregions within China [Wang et al, 2011a;Fu et al, 2012], the back trajectory analysis conducted here reduces the representativeness error of using only a few available sites to constrain China's total BC emissions.…”

“…We selected them because they are all located at rural mountains/hills without large local sources, representing the regional conditions. The three sites were used as observational constraints for Chinese BC emissions in previous modeling studies [Fu et al, 2012;Koch et al, 2009]. BC at the three sites were measured using the thermal-chemical method every third day, so the published monthly mean data are the averages from about 10 days' observations.…”

“…Koch et al [2009] reported that the majority of models participating in the AeroCom model intercomparison project underestimated BC surface measurements in China by more than 50%, suggesting a likely 50% underestimate of Chinese BC emissions by the inventory of Bond et al [2004] and Cofala et al [2007] used by the AeroCom models. Through comparison of Goddard Earth Observing System (GEOS)-Chem model results with BC measurements at 10 surface sites in China, Fu et al [2012] estimated that all previous bottom-up inventories underestimated BC emissions in China by at least 60%. Kondo et al [2011b] conducted a detailed modeling analysis of continuous BC measurements at a remote site (Cape Hedo) in East China Sea in combination with a chemical transport model (Community Multiscale Air Quality).…”

“…[3] Atmospheric measurements of BC concentrations at representative locations have provided independent "topdown" constraints on BC emissions, particularly when used in conjunction with chemical transport models or climate models that simulate the atmospheric processes of BC from emissions to atmospheric concentrations and deposition [Carmichael et al, 2003;Hakami et al, 2005;Park et al, 2005;Hu et al, 2009;Koch et al, 2009;Fu et al, 2012;Kondo et al, 2011b]. After allowing for the measurement uncertainty, one can evaluate model-calculated BC with available observations, attributing the difference to the bias in the emission inventory and/or model processes.…”

Village energy survey reveals missing rural raw coal in northern China: Significance in science and policy

“…A similar result was reported by Fu et al (2009) when they modeled the wintertime PM 2.5 pollution in Beijing; the simulated PM 2.5 concentration was considerably lower than that measured in the same period (Dan et al, 2004). In 2012, Fu et al (2012) simulated elemental carbon (EC) and organic carbon (OC) aerosols of China using an inventory based on CESY and compared the model results with surface measurements in order to derive "top-down" emission estimates of EC and OC. It was found that the model underestimated EC and OC concentration at almost all rural sites, particularly in January.…”