Fossil-driven secondary inorganic PM2.5 enhancement in the North China Plain: Evidence from carbon and nitrogen isotopes

Saehee Lim; Xiaoyang Yang; Meehye Lee; Gang Li; Yuanguan Gao; Xiaona Shang; Kai Zhang; Claudia I Czimczik; Xiaomei Xu; Min-Suk Bae; Kwang-Joo Moon; Kwonho Jeon

doi:10.1016/j.envpol.2020.115163

Fossil-driven secondary inorganic PM_2.5 enhancement in the North China Plain: Evidence from carbon and nitrogen isotopes

Environ Pollut. 2020 Nov;266(Pt 2):115163. doi: 10.1016/j.envpol.2020.115163. Epub 2020 Jul 6.

Authors

Saehee Lim¹, Xiaoyang Yang², Meehye Lee³, Gang Li², Yuanguan Gao², Xiaona Shang¹, Kai Zhang², Claudia I Czimczik⁴, Xiaomei Xu⁴, Min-Suk Bae⁵, Kwang-Joo Moon⁶, Kwonho Jeon⁶

Affiliations

¹ Dept. of Earth and Environmental Sciences, Korea University, 02841, Seoul, South Korea.
² State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing, 100012, China.
³ Dept. of Earth and Environmental Sciences, Korea University, 02841, Seoul, South Korea. Electronic address: meehye@korea.ac.kr.
⁴ Dept. of Earth System Science, University of California, 92697, Irvine, USA.
⁵ Environmental Engineering Department, Mokpo National University, 58554, Muan, South Korea.
⁶ National Institute of Environmental Research, 22689, Incheon, South Korea.

PMID: 32682020
DOI: 10.1016/j.envpol.2020.115163

Abstract

Measuring isotopic ratios in aerosol particles is a powerful tool for identifying major sources, particularly in separating fossil from non-fossil sources and investigating aerosol formation processes. We measured the radiocarbon, stable carbon, and stable nitrogen isotopic composition of PM_2.5 in Beijing (BJ) and Changdao (CD) in the North China Plain (NCP) from May to mid-June 2016. The mean PM_2.5 concentrations were 48.6 ± 28.2 μg m^-3 and 71.2 ± 29.0 μg m^-3 in BJ and CD, respectively, with a high contribution (∼66%) from secondary inorganic aerosol (SIA; NO₃^-, NH₄⁺, and SO₄^2-). The mean δ¹³C of total carbon (TC) and δ¹⁵N of total nitrogen (TN) values differed significantly between the two sites (p-value of <0.001): -25.1 ± 0.3‰ in BJ and -24.5 ± 0.4‰ in CD and 10.6 ± 1.8‰ in BJ and 5.0 ± 3.1‰ in CD, respectively. In BJ, the average δ¹⁵N (NH₄⁺) and δ¹⁵N (NO₃^-) values were 12.9 ± 2.3‰ and 5.2 ± 3.5‰, respectively. The ionic molar ratios and isotopic ratios suggest that NO₃^- in BJ was formed through the phase-equilibrium reaction of NH₄NO₃ under sufficient NH_{3 (g)} conditions, promoted by fossil-derived NH_{3 (g)} transported with southerly winds. In BJ, fossil fuel sources comprised 52 ± 7% of TC and 45 ± 28% of NH₄⁺ on average, estimated from radiocarbon (¹⁴C) analysis and the δ¹⁵N and isotope mixing model, respectively. These multiple-isotopic composition results emphasize that PM_2.5 enhancement is derived from fossil sources, in which vehicle emissions are a key contributor. The impact of the coal source was sporadically noticeable. Under regional influences, the fossil fuel-driven SIA led to the PM_2.5 enhancements. Our findings demonstrate that the multiple-isotope approach is highly advantageous to elucidate the key sources and limiting factors of secondary inorganic PM_2.5 aerosols.

Keywords: Fossil fuel; PM(2.5); Radiocarbon; Secondary inorganic aerosol; Stable isotope.

MeSH terms

Aerosols / analysis
Air Pollutants / analysis*
Beijing
Carbon / analysis*
Carbon Isotopes / analysis
China
Environmental Monitoring
Fossils
Nitrogen Isotopes / analysis
Particulate Matter / analysis

Substances

Aerosols
Air Pollutants
Carbon Isotopes
Nitrogen Isotopes
Particulate Matter
Carbon