Abstract
Recent changes of surface particulate matter (PM) concentration in the Seoul Metropolitan Area (SMA), South Korea, are puzzling. The long-term trend of surface PM concentration in the SMA declined in the 2000s, but since 2012 its concentrations have tended to incline, which is coincident with frequent severe hazes in South Korea. This increase puts the Korean government’s emission reduction efforts in jeopardy. This study reports that interannual variation of surface PM concentration in South Korea is closely linked with the interannual variations of wind speed. A 12-year (2004–2015) regional air quality simulation was conducted over East Asia (27-km) and over South Korea (9-km) to assess the impact of meteorology under constant anthropogenic emissions. Simulated PM concentrations show a strong negative correlation (i.e. R = −0.86) with regional wind speed, implying that reduced regional ventilation is likely associated with more stagnant conditions that cause severe pollutant episodes in South Korea. We conclude that the current PM concentration trend in South Korea is a combination of long-term decline by emission control efforts and short-term fluctuation of regional wind speed interannual variability. When the meteorology-driven variations are removed, PM concentrations in South Korea have declined continuously even after 2012.
Highlights
Since the early 2000s, the South Korean government has legislated a special act to improve air quality in the SMA11, with emphasis on the reduction of fugitive dust, mobile fuel type change, and residential heating source change
A 12-year simulation with a constant anthropogenic emission inventory was designed to isolate the interannual variation of surface particulate matter (PM) concentrations solely due to variations of meteorology (See method)
After testing multiple meteorological variables, we found a significant association of wind speed and surface PM concentrations
Summary
In order to investigate the interannual variation of surface PM concentration in the SMA, we conducted a 12-year simulation using a regional air quality modeling system. The Weather Research and Forecasting Model (WRF), the Sparse Matrix Operator Kernel Emission (SMOKE), and the Community Multiscale Air Quality (CMAQ) models were utilized to simulate meteorology and chemistry over East Asia (27-km domain) and over South Korea (9-km domain). Clean Air Policy Support System (CAPSS) 2007 for South Korea and Intercontinental Chemical Transport Experiment Phase-B (INTEX-B) 2006 emission inventory for other Asian countries, were used for the 12-year simulation to isolate the impact of interannual variability of anthropogenic emissions. (1) A recent study on the regional emission attribution to the South Korea suggests that the relative attribution of foreign emission sources is not sensitive to inter-annual variation of meteorology[55], contributing around 60% of the SMA PM concentration. Careful and continuous monitoring of diesel vehicle emissions is necessary due to their high uncertainty in emissions factors as we have learned from the Volkswagen emission scandal[56]
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