Biomass Burning Contributions to Ambient Volatile Organic Compounds (VOCs) in the Harvest Season in Beijing, China

Abstract:

Volatile organic compounds (VOCs) play a fundamental role in the tropospheric chemistry as key precursors of ozone and secondary organic aerosol (SOA), and many VOC species have an adverse impact on human health. Therefore, VOCs are of great concern. Biomass burning, which is recognized as an important source of VOCs in China, has a significant effect on air pollution and climate change. Recent studies have reported some source profiles of VOCs emitted from biomass burning in China, and emission inventories have also been developed to estimate the biomass burning emissions. Nevertheless, very little is known about the emission characteristics of biomass burning, nor its contributions to ambient VOCs. This work presents the results from a continuous measurement of 108 VOC compounds by an online GC-MS/FID system at a receptor site in Beijing from October 1-14, 2014. Several biomass burning plumes were identified by extremely high level of acetonitrile, which is an excellent signature of biomass burning. The emission ratios of six VOCs species relative to acetonitrile were determined by enhancement ratio method. The contributions of biomass burning to ambient VOCs were also explored. Results show that the mixing ratios of ambient VOCs in biomass burning days were over twice as that in non-burning days. And biomass burning accounted for 25.1% (benzene), 24.6% (toluene), 18.8% (acetone), 24.9% (MEK), 29.4% (MVK), and 18.2% (n-hexanal) of the ambient mixing ratios, respectively. PMF analysis indicated that the contributions of biomass burning to VOCs increased from 5.5% to 12.7% on average in biomass burning days, which revealed that the high level of ambient VOCs in Beijing during this period can be partly attributed to extensive biomass burning. Our study will be helpful to better understand biomass burning emissions in China, as well as to explore the contributions of biomass burning to haze formation in the harvest season.