Abstract. We simulated elemental carbon (EC) and organic carbon (OC) aerosols in China and compared 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 included in the model state-of-the-science Chinese "bottom-up" emission inventories for EC (1.92 TgC yr −1 ) and OC (3.95 TgC yr −1 ), as well as updated secondary OC formation pathways. The average simulated annual mean EC concentration at rural and background sites was 1.1 µgC m −3 , 56 % lower than the observed 2.5 µgC m −3 . The average simulated annual mean OC concentration at rural and background sites was 3.4 µgC m −3 , 76 % lower than the observed 14 µgC m −3 . Multiple regression to fit surface monthly mean EC observations at rural and background sites yielded the best estimate of Chinese EC source of 3.05 ± 0.78 TgC yr −1 . Based on the topdown EC emission estimate and observed seasonal primary OC/EC ratios, we estimated Chinese OC emissions to be 6.67 ± 1.30 TgC yr −1 . Using these top-down estimates, the simulated average annual mean EC concentration at rural and background sites was significantly improved to 1.9 µgC m −3 . However, the model still significantly underestimated observed OC in all seasons (simulated average annual mean OC at rural and background sites was 5.4 µgC m −3 ), 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 four shortcomings in the current bottom-up inventories of Chinese carbonaceous aerosols: (1) the anthropogenic source is underestimated on a national scale, particularly for OC; (2) the spatiotemporal distributions of emissions are misrepresented; (3) there is a missing source in western China, likely associated with the use of biofuels or other low-quality fuels for heating; and (4) sources in fall are not well represented, either because the seasonal shifting of Published by Copernicus Publications on behalf of the European Geosciences Union. T.-M. Fu et al.: Carbonaceous aerosols in Chinaemissions and/or secondary formation are poorly captured or because specific fall emission events are missing. In addition, secondary production of OC in China is severely underestimated. More regional measurements with better spatiotemporal coverage are needed to resolve these shortcomings.

The spatial distribution of the aerosols over 86 Chinese cities was reconstructed from air pollution index (API) records for summer 2000 to winter 2006. PM₁₀ (particulate matter ≤10 μm) mass concentrations were calculated for days when PM₁₀ was the principal pollutant, these accounted for 91.6% of the total 150 428 recorded days. The 83 cities in mid-eastern China (100° E to 130° E) were separated into three latitudinal zones using natural landscape features as boundaries. Areas with high PM₁₀ level in northern China (127 to 192 μg m⁻³) included Urumchi, Lanzhou-Xining, Weinan-Xi'an, Taiyuan-Datong-Yangquan-Changzhi, Pingdingshan-Kaifeng, Beijing-Tianjin-Shijiazhuang, Jinan, and Shenyang-Anshan-Fushun; in the middle zone, high PM₁₀ (119–147 μg m⁻³) occurred at Chongqing-Chengdu-Luzhou, Changsha-Wuhan, and Nanjing-Hangzhou; in the southern zone, only four cities (Qujing, Guiyang, Guangzhou and Shaoguan) showed PM₁₀ concentration >80 μg m⁻³. The median PM₁₀ concentration decreased from 108 μg m⁻³ for the northern cities to 95 μg m⁻³ and 55 μg m⁻³ for the middle and southern zones, respectively. PM₁₀ concentration and the APIs both exhibited wintertime maxima, summertime minima, and the second highest values in spring. PM₁₀showed evidence for a decreasing trend for the northern cities while in the other zones urban PM₁₀ levels fluctuated, but showed no obvious change over time. The spatial distribution of PM₁₀ was compared with the emissions, and the relationship between the surface PM₁₀ concentration and the aerosol optical depth (AOD) was also discussed

[1] We present a new top-down approach that spatially constrains the amount of aerosol emissions using satellite (Moderate Resolution Imaging Spectroradiometer (MODIS)) observed radiances with the adjoint of a chemistry transport model (GEOS-Chem). This paper aims to demonstrate the approach through applying it to a case study that yields the following emission estimates over China for April 2008: 1.73 Tg for SO 2 , 0.72 Tg for NH 3 , 1.38 Tg for NO x , 0.10 Tg for black carbon, and 0.18 Tg for organic carbon from anthropogenic sources, which reflects, respectively, a reduction of 33.5%, 34.5%, 18.8%, 9.1%, and 15% in comparison to the prior bottom-up inventories of INTEX-B 2006. The mineral dust emission from the online dust entrainment and mobilization module is reduced by 56.4% of 19.02 to 8.30 Tg. Compared to the prior simulation, the posterior simulation shows a much better agreement with the following independent measurements: aerosol optical depth (AOD) measured by AERONET sun-spectrophotometers and retrieved from Multi-angle Imaging SpectroRadiometer (MISR), atmospheric NO 2 and SO 2 columnar amount retrieved from Ozone Monitoring Instrument (OMI), and in situ data of sulfate-nitrate-ammonium and PM 10 (particular matter with aerodynamic diameter less than 10 mm) mass concentrations over both anthropogenic pollution and dust source regions. Assuming the bottom-up (prior) anthropogenic emissions are the best estimates for their base year of 2006, the overwhelming reduction in the posterior (top-down) estimate indicates less emission in April 2008 especially for the SO 2 tracer in the central and eastern parts of China, and/or an overestimation in the prior emission. The former is supported by the AOD change detected by MODIS and MISR sensors, while the latter is likely the case for NO x and NH 3 emissions because no evidence shows that their atmospheric concentration has declined over China. With the promising results shown in this study, continuous efforts are needed toward a holistic and comprehensive inversion of emission using multisensor remote sensing data (of trace gases and aerosols) for constraining aerosol primary and precursor emissions at various temporal and spatial scales.

A B S T R A C T Concentrations of organic carbon (OC), elemental carbon (EC), selected trace elements and water-soluble (WS) ionswere determined for samples collected from August 2004 to February 2005 to assess the aerosol background at two remote sites in China. The OC and EC concentrations in PM 10 from near the Tibetan Plateau at Zhuzhang (ZUZ) were comparable with other background sites, averaging 3.1 and 0.34 μg m −3 , respectively, with no pronounced seasonality. At Akdala (AKD) on northern margin of the Zhungaer Basin, the average concentrations were similar (mean OC = 2.9 μg m −3 and EC = 0.35 μg m −3 ), but the concentrations were higher in winter. The aerosol mass at both sites was dominated by OC and SO 4 2− , but a stronger contribution from soil dust was observed at AKD. At ZUZ, NO 3 − showed a unique weather-related fluctuation in PM 10 with a periodicity of ∼1 week. Anthropogenic sources in the Sichuan Basin and southeastern Yunnan Province evidently influence ZUZ in summer and autumn while pollutants from Russia and the China-Mongolia border affect AKD nearly all year. The identification of these upwind sources demonstrates that transboundary transport needs to be taken into account when assessing air quality in remote parts of China.