Abstract
A record-breaking severe heat wave was recorded in southeast Korea from 11 July to 15 August 2018, and the numerical sensitivity simulations of volatile organic compound (VOC) to secondarily generated particulate matter with diameter of less than 2.5 µm (PM2.5) concentrations were studied in the Busan and Ulsan metropolitan areas in southeast Korea. A weather research and forecasting (WRF) model coupled with chemistry (WRF-Chem) was employed, and we carried out VOC emission sensitivity simulations to investigate variations in PM2.5 concentrations during the heat wave period that occurred from 11 July to 15 August 2018. In our study, when anthropogenic VOC emissions from the Comprehensive Regional Emissions Inventory for Atmospheric Transport Experiment-2015 (CREATE-2015) inventory were increased by approximately a factor of five in southeast Korea, a better agreement with observations of PM2.5 mass concentrations was simulated, implying an underestimation of anthropogenic VOC emissions over southeast Korea. The simulated secondary organic aerosol (SOA) fraction, in particular, showed greater dominance during high temperature periods such as 19–21 July, 2018, with the SOA fractions of 42.3% (in Busan) and 34.3% (in Ulsan) among a sub-total of seven inorganic and organic components. This is considerably higher than observed annual mean organic carbon (OC) fraction (28.4 ± 4%) among seven components, indicating the enhancement of secondary organic aerosols induced by photochemical reactions during the heat wave period in both metropolitan areas. The PM2.5 to PM10 ratios were 0.69 and 0.74, on average, during the study period in the two cities. These were also significantly higher than the typical range in those cities, which was 0.5–0.6 in 2018. Our simulations implied that extremely high temperatures with no precipitation are significantly important to the secondary generation of PM2.5 with higher secondary organic aerosol fraction via photochemical reactions in southeastern Korean cities. Other possible relationships between anthropogenic VOC emissions and temperature during the heat wave episode are also discussed in this study.
Highlights
Particulate matter with diameter of less than 2.5 μm (PM2.5 ) concentrations are affected by both local emissions and the long-range transport of air pollutants [1,2,3]
(in Ulsan) among a sub-total of seven inorganic and organic components. This is considerably higher than observed annual mean organic carbon (OC) fraction (28.4 ± 4%) among seven components, indicating the enhancement of secondary organic aerosols induced by photochemical reactions during the heat wave period in both metropolitan areas
We investigated the seasonal characteristics of backward trajectories and synoptic weather chart and found out that frequent long-range transport (LRT) processes dominated, originating from China inland, and extremely high
Summary
Particulate matter with diameter of less than 2.5 μm (PM2.5 ) concentrations are affected by both local emissions and the long-range transport of air pollutants [1,2,3]. In Busan and Ulsan Metropolitan areas (hereafter BMA and UMA, respectively), extremely high temperatures were continuously observed from 11 July to 15 August 2018, and this period was recorded as a record-breaking severe heat wave. During this period, heat wave advisories and heat wave warnings simultaneously with notably polluted air quality were issued for 19–20 July. A weather research and forecasting (WRF) model coupled with chemistry (WRF-Chem) was employed to study the heat wave effects on air quality in the BMA and UMA during the record-breaking heat wave period in 2018 Other discussions, such as the possible relationship between anthropogenic evaporative VOC emissions and temperature during the heat wave period, are given in this study
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