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Volume 17, issue 8 | Copyright

Special issue: Regional transport and transformation of air pollution in...

Atmos. Chem. Phys., 17, 5205-5219, 2017
https://doi.org/10.5194/acp-17-5205-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 21 Apr 2017

Research article | 21 Apr 2017

Direct radiative effect of carbonaceous aerosols from crop residue burning during the summer harvest season in East China

Huan Yao1, Yu Song1, Mingxu Liu1, Scott Archer-Nicholls2, Douglas Lowe3, Gordon McFiggans3, Tingting Xu1, Pin Du1, Jianfeng Li1, Yusheng Wu1, Min Hu1, Chun Zhao4, and Tong Zhu1 Huan Yao et al.
  • 1State Key Joint Laboratory of Environmental Simulation and Pollution Control, Department of Environmental Science, Peking University, Beijing, China
  • 2Centre for Atmospheric Science, University of Cambridge, Cambridge, UK
  • 3Centre for Atmospheric Sciences, School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Manchester, UK
  • 4School of Earth and Space Science, University of Science and Technology of China, Hefei, Anhui, China

Abstract. East China experiences extensive crop residue burnings in fields during harvest season. The direct radiative effect (DRE) of carbonaceous aerosols from crop residue burning in June 2013 in East China was investigated using the Weather Research and Forecasting Model coupled with Chemistry (WRF-Chem). Absorption of organic aerosol (OA) in the presence of brown carbon was considered using the parameterization of Saleh et al. (2014), in which the imaginary part of the OA refractive index is a function of wavelength and the ratio of black carbon (BC) and OA. The carbonaceous emissions from crop fires were estimated using the Moderate Resolution Imaging Spectroradiometer (MODIS) fire radiative power (FRP) product with a localized crop-burning-sourced BC-to-organic carbon (OC) ratio emission ratio of 0.27. Evaluation of the model results with in situ measurements of particulate matter with aerodynamic diameter less than 2.5µm (PM2. 5) chemical composition, MODIS aerosol optical depth (AOD) detections and meteorological observations showed that this model was able to reproduce the magnitude, spatial variation and optical characteristics of carbonaceous aerosol pollution. The observed BC and OC peak concentrations at the site in Suixi, Anhui province, during the 2013 wheat burning season reached 55.3µgm−3 and 157.9µgm−3. WRF-Chem simulations reproduced these trends with a correlation coefficient of 0.74, estimating that crop residue burning contributed 86 and 90% of peak BC and OC, respectively. The simulated hourly DRE from crop residue burning at the top of atmosphere (TOA) reached a maximum of +22.66Wm−2 at the Suixi site. On average, the simulations showed that the crop residue burning introduced a net positive DRE of +0.14Wm−2 at TOA throughout East China, with BC from this source as the main heating contributor (+0.79Wm−2). The OA DRE from crop burning (−0.22Wm−2) was a combined effect of the positive DRE of absorption (+0.21Wm−2) and a stronger negative DRE of scattering (−0.43Wm−2). Sensitivity tests showed that the DRE of OA absorption strongly depended on the imaginary part of the OA refractive index, the BC-to-OA emission ratio from crop residue burning and the assumed mixing state of the aerosol, whereby the volume mixing treatment resulted in a higher positive DRE compared to the core–shell treatment. The BC mixing state and associated absorption enhancement during BC aging processes will be investigated in detail in future research.

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