Light-absorption enhancement of black carbon in the Asian outflow inferred from airborne SP2 and in-situ measurements during KORUS-AQ

Chaeyoon Cho; Joshua P Schwarz; Anne E Perring; Kara D Lamb; Yutaka Kondo; Jong-Uk Park; Do-Hyeon Park; Kyuseok Shim; Jin-Soo Park; Rokjin J Park; Meehye Lee; Chang-Keun Song; Sang-Woo Kim

doi:10.1016/j.scitotenv.2021.145531

Light-absorption enhancement of black carbon in the Asian outflow inferred from airborne SP2 and in-situ measurements during KORUS-AQ

Sci Total Environ. 2021 Jun 15:773:145531. doi: 10.1016/j.scitotenv.2021.145531. Epub 2021 Feb 1.

Authors

Affiliations

¹ School of Earth and Environmental Sciences, Seoul National University, Seoul 08826, Republic of Korea.
² NOAA Earth System Research Laboratory (ESRL), Chemical Sciences Division, Boulder, CO 80305, USA.
³ NOAA Earth System Research Laboratory (ESRL), Chemical Sciences Division, Boulder, CO 80305, USA; Cooperative Institute for Research in the Environmental Sciences (CIRES), University of Colorado, Boulder, CO 80309, USA.
⁴ National Institute for Polar Research, Tachikawa, Tokyo 190-8518, Japan.
⁵ National Institute of Environmental Research, Incheon 22689, Republic of Korea.
⁶ Department of Earth and Environmental Sciences, Korea University, Seoul 02841, Republic of Korea.
⁷ School of Urban and Environmental Engineering, Ulsan National Institute of Science and Technology, Ulsan 44919, Republic of Korea.
⁸ School of Earth and Environmental Sciences, Seoul National University, Seoul 08826, Republic of Korea. Electronic address: sangwookim@snu.ac.kr.

PMID: 33582332
DOI: 10.1016/j.scitotenv.2021.145531

Abstract

We investigated the changes in the size distribution, coating thickness, and mass absorption cross-section (MAC) of black carbon (BC) with aging and estimated the light absorption enhancement (E_abs) in the Asian outflow from airborne in-situ measurements during 2016 KORUS-AQ campaign. The BC number concentration decreased, but mass mean diameter increased with increasing altitude in the West Coast (WC) and Seoul Metropolitan Area (SMA), reflecting the contrast between freshly emitted BC-containing particles at the surface and more aged aerosol associated with aggregation during vertical mixing and transport. Contradistinctively, BC number and mass size distributions were relatively invariant with altitude over the Yellow Sea (YS) because sufficiently aged BC from eastern China were horizontally transported to all altitudes over the YS, and there are no significant sources at the surface. The averaged inferred MAC of refractory BC in three regions reflecting differences in their size distributions increased to 9.8 ± 1.0 m² g^-1 (YS), 9.3 ± 0.9 m² g^-1 (WC), and 8.2 ± 0.9 m² g^-1 (SMA) as BC coating thickness increased from 20 nm to 120 nm. The absorption coefficient of BC calculated from the coating thickness and MAC were highly correlated with the filter-based absorption measurements with the slope of 1.16 and R² of 0.96 at 550 nm, revealing that the thickly coated BC had a large MAC and absorption coefficient. The E_abs due to the inferred coatings was estimated as 1.0-1.6, which was about 30% lower than those from climate models and laboratory experiments, suggesting that the increase in the BC absorption by the coatings in the Asian outflow is not as large as calculated in the previous studies. Organics contributed to the largest E_abs accounting for 69% (YS), 61% (WC), and 64% (SMA). This implies that organics are largely responsible for the lensing effect of BC rather than sulfates in the Asian outflow.

Keywords: Absorption enhancement; Aging process; Black carbon; KORUS-AQ; SP2.