Neglected biomass burning emissions of air pollutants in China-views from the corncob burning test, emission estimation, and simulations

Corncob is one of the major biomass sources and widely adopted as fuel in rural China. However, only few studies have discussed the emissions from corncob burning. The negligence of corncob burning emissions has resulted in biased or even unreasonable biomass burning emission results. In this study, the emission factors (EFs) of corncob burning were measured by the burning test simulation and dilution sampling system. Then, the measured EFs, field surveys, and GEOS-Chem simulation were adopted to estimate the emissions from corncob burning. The EFs of fine particles (PM2.5), carbon monoxide (CO), sulfur dioxide (SO2), nitric oxide (NO), nitric oxides (NOX), ammonia (NH3), the totally measured 13 volatile organic compounds (TVOCs), organic carbon (OC), elemental carbon (EC) and the sum of water-soluble ions (Na+, K+, Mg-2+, Ca-2+, NH4+, Cl-, NO3- and SO42-) (SWSI) for corncob were 7.95, 60.53, 0.29, 1.38, 3.46, 0.35, 3.91, 1.21, 0.19 and 0.53 g kg(- 1), respectively. The emissions of PM2.5, CO, SO2, NO, NOX, NH3, TVOCs, OC, EC and SWSI in 2014 were 312.20, 2377.1, 11.39, 54.19, 135.87, 13.74, 153.55, 47.52, 7.46 and 20.77 Gg, respectively. These emissions have the same change tendency, wherein the emission in 2014 were approximately 0.42, 0.50, 0.64 and 0.85 times those in 1992, 2002, 2007 and 2012, respectively. The comparison with other straw highlighted the considerable emissions of corncob burning in China. The biomass burning emissions have been substantially underestimated by 2.6%-36.2% in previous studies, wherein corncob burning emissions were not considered. Additionally, the GEOS-Chem simulation results showed that corncob burning produced much higher concentration values than corn straw burning. Our study provided credible evidence to confirm the important emission contributions of corncob burning to biomass burning. It can also help improve the biomass burning estimation and air quality modeling results in the future.