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

Huan Yao,Chun Zhao,Pin Du,Douglas Lowe,Tingting Xu,Jianfeng Li,Min Hu,Mingxu Liu,Tong Zhu,Gordon Mcfiggans,Scott Archer-Nicholls,Yusheng Wu,Yu Song

doi:10.5194/acp-17-5205-2017

Abstract

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 2.5 µm (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 55.3 µg m−3 and 157.9 µg m−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 +22.66 W m−2 at the Suixi site. On average, the simulations showed that the crop residue burning introduced a net positive DRE of +0.14 W m−2 at TOA throughout East China, with BC from this source as the main heating contributor (+0.79 W m−2). The OA DRE from crop burning (−0.22 W m−2) was a combined effect of the positive DRE of absorption (+0.21 W m−2) and a stronger negative DRE of scattering (−0.43 W m−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.

Highlights

Carbonaceous aerosols emitted from biomass burning contributes 42 and 74 % of global black carbon (BC) and organic carbon (OC) emissions, respectively (Bond et al, 2004), playing an important role in the radiation budget system (Chung et al, 2012; Hobbs et al, 1997; Jacobson, 2014)
When the BC-toOA ratio was altered to 0.18 (Li et al, 2007) and 0.42 (Hays et al, 2005) by changing the BC emission factor from crop residue burning alone with that of organic aerosol (OA) constant, the direct radiative effect (DRE) of OA absorption was estimated to be +0.33 and +0.13 W m−2 (Supplement Table S2), respectively. These results indicated that the kOA and the BC-to-OC emission ratio were critical for estimating DRE of OA absorption and efforts are still needed to update the BC-to-OC ratio to observations in China
The DRE of carbonaceous aerosols from crop residue burning in June 2013 in Eastern China was investigated using WRF-Chem

Summary

Introduction

Carbonaceous aerosols emitted from biomass burning contributes 42 and 74 % of global black carbon (BC) and organic carbon (OC) emissions, respectively (Bond et al, 2004), playing an important role in the radiation budget system (Chung et al, 2012; Hobbs et al, 1997; Jacobson, 2014). H. Yao et al.: Direct radiative effect of carbonaceous aerosols. Assessment Report estimated that BC from biomass burning introduced a global mean direct radiative forcing (DRF) of approximately +0.2 (+0.03 to +0.4) W m−2, while that of organic aerosol (OA) from biomass burning was about the same magnitude with the opposite sign (Bond et al, 2013; Stocker, 2014). DRF is a measure of the change in direct radiative effect (DRE) relative to preindustrial conditions, defined as prior to the year 1750 AD by the IPCC. DRE could be a more exhaustive gauge for comparisons between models and observations (Heald et al, 2014)

Methods

Results

Conclusion