Abstract
Secondary organic carbon (SOC) formation and its effects on human health require better understanding in Chinese megacities characterized by a severe particulate pollution and robust economic reform. This study investigated organic carbon (OC) and elemental carbon (EC) in PM2.5 and PM0.25 collected 8–20 March 2012. Samples were collected inside and outside a classroom in a middle school at Xi’an. On average, OC and EC accounted for 20%–30% of the particulate matter (PM) mass concentration. By applying the EC-tracer method, SOC’s contribution to OC in both PM size fractions was demonstrated. The observed changes in SOC:OC ratios can be attributed to variations in the primary production processes, the photochemical reactions, the intensity of free radicals, and the meteorological conditions. Total carbon (TC) source apportionment by formula derivation showed that coal combustion, motor vehicle exhaust, and secondary formation were the major sources of carbonaceous aerosol. Coal combustion appeared to be the largest contributor to TC (50%), followed by motor vehicle exhaust (25%) and SOC (18%) in both size fractions.
Highlights
Organic carbon (OC) and elemental carbon (EC) are the major components of ambient atmospheric aerosols that originate from natural and anthropogenic combustion sources
A bias may have been created by the input of PM0.25 coming from the street via a window, while the outdoor sampling site located within the school was less affected
PM2.5 and PM0.25 samples collected from 8 to 20 March 2012, inside and outside a classroom in a middle school at Xi’an, China, were used to feature organic carbon (OC) and EC according to two different particle size fractions and to identify Secondary organic carbon (SOC) by various methods in order to understand the SOC formation pathways and the source apportionment of Total carbon (TC)
Summary
Organic carbon (OC) and elemental carbon (EC) are the major components of ambient atmospheric aerosols that originate from natural and anthropogenic combustion sources. EC is a primary product emitted from combustion processes and OC exists in two forms: (i) Primary. OC (POC), which is directly emitted into the atmosphere either from fossil fuel combustion by industries, road transportation, and the residential sector or by biomass burning; and (ii) secondary OC (SOC), which is formed through atmospheric oxidation of volatile organic compounds (VOCs) and gas-to-particle conversion processes. Huang et al showed that the severe haze pollution events during winters in China were generally caused by secondary aerosol formation, which contributed 30%–77% of PM2.5 (particulate matter with aerodynamic diameters ≤ 2.5 μm) and 44%–71% of organic aerosols [23]
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