Carbon and nitrogen isotopic composition of PM2.5 at a periurban Mt. Taehwa near Seoul and over the Yellow Sea

Abstract:

Fine particular matter (PM_2.5) is a major contributor to poor air quality in East Asia, with detrimental effects on air quality and climate. The elemental and isotopic composition of PM_2.5 is powerful proxy for identifying emission sources, understanding atmospheric processing, and mitigating emissions of PM_2.5. Here, we present a time-series of the elemental and isotopic composition of PM_2.5 in East Asia, sampled at a periurban site (Mt. Taehwa, South Korea, August - October 2014) and over the Yellow Sea (onboard RV Gisang 1, November 2014). We measured the radiocarbon (¹⁴C) content of total carbon (TC) and elemental carbon (EC) with accelerator mass spectrometry and the carbon and nitrogen elemental and stable isotopic composition of bulk PM_2.5 with isotope ratio mass spectrometry. At Mt. Taehwa, EC was depleted in ¹⁴C (fM-EC=0.224±0.071 (ave±SD, n=6)). The bulk PM_2.5 was enriched in ¹⁴C above natural levels (fM-TC=1.19±0.47, n=9), with a δ¹³C of -25.6±0.5 (n=7), and a δ¹⁵N of 14.6±3.8 (n=4), and was strongly enriched in nitrogen (C:N=2.8±1.4, n=16). Over the Yellow Sea, bulk PM_2.5 was depleted in ¹⁴C (fM-TC=0.57±0.07, n=5), with a δ¹³C of -24.2±0.8 (n=3), and a δ¹⁵N of 5.2±4.3 (n=3); EC was too small for ¹⁴C analysis.

 Our results confirm that periurban Mt. Taehwa site is exposed to combustion plumes of fossil fuels, especially from on-road sources. PM_2.5 over the Yellow Sea turned out to be a mixture of fossil and biogenic emissions and experience more intense atmospheric processes. This isotope-based source apportionment of PM_2.5 is a first step to characterize major sources of aerosols at Taehwa Research Forest, which was established to examine interactions of megacity and biogenic emissions and their impact on air quality.