10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Comprehensive Analysis of Carbonaceous Gases and Particles in Beijing, 2016
SHUO YANG, Kebin He, Fengkui Duan, Tsinghua University
Abstract Number: 505 Working Group: Carbonaceous Aerosol
Abstract Carbon is one of the fundamental chemical elements and serves as the basic materials of all known life on earth. It could exist in gas or solid phase in the atmosphere, namely carbonaceous gases and particles. Carbonaceous particles (mainly refers to organic aerosol (OA) and elemental species) were the major components in PM2.5, which has caused extreme haze pollution around world, especially the North China Plain (NCP) region in recent decades, imposing detrimental effects on visibility, human health, and radiation forces.
Globally, around 20% of OA were primarily emitted (POA) and the rest were secondarily formed (that is, SOA, secondary organic aerosol). In urban site like Beijing, SOA could take up 30-77% of total OA concentration or even 44-71% of total PM2.5 mass, it was the crucial constituents of atmospheric particulates.
However, unlike other components in PM2.5, detailed composition and chemical evolution of carbonaceous particle from gaseous precursors were intricate and poorly-analyzed. The integrated observation of carbonaceous gases and particles concentration and exploration of interior connections of gas-to-particle transformation is lacking.
In that case, we conducted a long-time continuous hourly-based observation and delineated the overall concentration level, diurnal variation profile of all carbon-species including carbon dioxide (CO2), carbon monoxide (CO), methane (CH4), volatile organic compounds (VOCs), non-methane hydrocarbon (NMHC), and particle organic carbon (OC), Elemental carbon (EC), water soluble organic compounds (WSOC) in Beijing, 2016.
The results indicated that unlike the inert carbonaceous gases (CO, CO2 and CH4) with one-peak in diurnal profile, the reactive VOCs/CO showed the double-peak pattern, with a pronounced peak at midnight, the same as carbonaceous particle OC/EC ratio and WSOC1/WSOC2.5 (WSOC in PM1 and PM2.5, respectively) ratio, especially in winter.
high positive relationship between carbonaceous particles with VOCs precursors level (OC-VOCs, WSOC1-VOCs, WSOC2.5-VOCS), and meteorological RH condition (RH-OC and RH-WSOC) were observed (with R-sqaures above 0.75), indicating VOCs and RH were the major factors facilitating high organic mass accumulation in the atmosphere. Moreover, RH with different ranges imposed different influence on WSOC concentration in PM1 and PM2.5, respectively. WSOC1 concentrations were enhanced largely with RH ranging from 50% -80%, but for WSOC1-2.5 formation, the corresponding RH level changed to larger than 80%.
An F-factor method (based on logarithmic calculation of carbonaceous particles concentration (μgC m-3) divided by that of carbonaceous gases) was established to reflect gas-particle relationship of carbon and has been verified effective in indicating the haze events and revealing the existence form of carbon in the atmosphere. higher F-factor in winter indicated that carbon was prone to exist in particle phase in Beijing. And higher F-factor (>0.15) corresponded with PM2.5 load larger than 150 μg m-3, while a lower value (<0.05) reflected a clean condition (PM2.5 less than 35 μg m-3)
In this work, we provided the first comprehensive mass closure observation of all carbonaceous gases and particles in the atmosphere, which helped broaden our understanding in carbon cycle and secondary organic aerosol formation. Our new insights into SOC formation may contribute to an accurate evaluation of conversion from carbonaceous gases to particles, specifically, the effect on WSOC formation from VOCs precursors in the atmosphere.