Effects of seasonal management programs on PM2.5 in Seoul and Beijing using DN-PMF: Collaborative efforts from the Korea-China joint research.

South Korea and China have implemented increasingly stringent mitigation measures to reduce the health risks from PM2.5 exposure, jointly conducting a ground-based air quality observation study in Northeast Asia. Dispersion normalized positive matrix factorization (DN-PMF) was used to identify PM2.5 sources in Seoul and Beijing and assess the effectiveness of the seasonal management programs (SMPs) through a comparative study. Samples were collected during three periods: January-December 2019, September 2020-May 2021, and July 2021-March 2022. In Seoul, ten sources were resolved (Secondary nitrate: 8.67 µg/m3, 34 %, Secondary sulfate: 5.67 µg/m3, 22 %, Motor vehicle: 1.83 µg/m3, 7.2 %, Biomass burning: 2.30 µg/m3, 9.1 %, Residual oil combustion: 1.66 µg/m3, 6.5 %, Industry: 2.15 µg/m3, 8.5 %, Incinerator: 1.39 µg/m3, 5.5 %, Coal combustion: 0.363 µg/m3, 1.4 %, Road dust/soil: 0.941 µg/m3, 3.7 %, Aged sea salt: 0.356 µg/m3, 1.4 %). The SMP significantly decreased PM2.5 mass concentrations and source contributions of motor vehicle, residual oil combustion, industry, coal combustion, and biomass burning sources (p-value < 0.05). For Seoul, the reduction effects of the SMPs were evident even considering the influence of the natural meteorological variations and the responses to COVID-19. In Beijing, nine sources were resolved (Secondary nitrate: 12.6 µg/m3, 28 %, Sulfate: 8.27 µg/m3, 18 %, Motor vehicle: 3.77 µg/m3, 8.4 %, Biomass burning: 2.70 µg/m3, 6.0 %, Incinerator: 4.50 µg/m3, 10 %, Coal combustion: 3.52 µg/m3, 7.8 %, Industry: 5.01 µg/m3, 11 %, Road dust/soil: 2.92 µg/m3, 6.5 %, Aged sea salt: 1.63 µg/m3, 3.6 %). Significant reductions in PM2.5 mass concentrations and source contributions of industry, coal combustion, and incinerator (p-value < 0.05) were observed, attributed to the SMP and additional measures enforced before the 2022 Beijing Winter Olympics. Unlike comparing PM2.5 mass concentration variations using conventional methods, investigation of the source contribution variations of PM2.5 by using DN-PMF can provide a deeper understanding of the effectiveness of the air quality management policies.

Fossil and non-fossil sources of the carbonaceous component of PM2.5 in forest and urban areas.

Atmospheric particulate matter (PM2.5) can damage human health. Biogenic organic compounds emitted from trees may increase the concentration of PM2.5 via formation of secondary aerosols. Therefore, the role of biogenic emissions in PM2.5 formation and the sources of PM2.5 need to be investigated. Dual carbon isotope and levoglucosan analyses are powerful tools to track the sources of total carbon (TC) in PM2.5. We collected a total of 47 PM2.5 samples from 2019 to 2020 inside a pine forest and in urban areas in South Korea. The average δ13C and Δ14C of TC in PM2.5 at the Taehwa Research Forest (TRF) were - 25.7 and - 380.7‰, respectively, which were not significantly different from those collected at Seoul National University (SNU) in urban areas. Contribution of fossil fuel, C3-, and C4- plants to carbonaceous component of PM2.5 were 52, 27, and 21% at SNU, whereas those were 46, 35, and 19% at TRF, respectively. The biomass burning tracer, levoglucosan, was most abundant in winter and correlated with the contribution of C4 plants derived carbon. Results indicate that biogenic aerosols emitted from trees is less likely to be an important source of PM2.5 and that trees can act as a bio-filter to reduce PM2.5.