Quantification of regional contributions to fine particles at downwind areas under Asian continental outflows during winter 2014

Effective reduction strategies for fine particles (PM2.5) in areas downwind of Asian continental outflows require quantification of regional and local contributions to PM2.5. To quantify the chemical compositions of long-range transported and locally produced aerosol particles during a severe haze episode, aerosol particles were collected at a remote background site in Baengnyeong Island (BN) and an inland urban site in Daejeon (DJ) in the Republic of Korea from 7 February to 6 March 2014. Aerosol samples were analyzed for PM2.5, inorganic ions, carbonaceous species, and heavy metals. During a severe haze episode (EP) from 22 February to 1 March 2014, elevated PM2.5 concentrations of 73.3 ± 18.3 μg m−3 and 74.9 ± 14.3 μg m−3 were measured at the BN and DJ sites, respectively. Although both sites were influenced by long-range transported haze from China, SO42− was determined to be the most abundant species at the BN site during the EP period with an average of 29.9 ± 11.5 μg m−3, whereas NO3− was the most abundant species at the DJ site with an average of 20.9 ± 5.4 μg m−3. Low NO2 concentrations (2.6 ± 1.9 ppb) and a northwesterly air-mass trajectory suggest that most air pollutants at the BN site underwent long-range transport from China during the EP period and were minimally affected by local emissions from the Korean Peninsula. The chemical components of long-range transported and locally produced PM2.5 were quantified using arsenic (As) as a tracer for long-range transported haze from China. It was found that large fractions of SO42− (87% ± 31%), OC (70% ± 16%), and NH4+ (65% ± 10%) at the DJ site underwent long-range transport from China during the EP period. However, a significant fraction (67% ± 15%) of NO3− was determined to be secondarily produced from NO2 emitted from local sources during the EP period. On average, 34% of PM2.5 was locally produced at the DJ site during the EP period. Local production of PM2.5 is attributed mainly to NO3− (57%), followed by NH4+ (18%), SO42− (11%), and OC (9%). Results from this work suggest that when severe haze undergoes long-range transport from China to the Korean Peninsula during winter, a reduction of local NO2 emissions is the most effective strategy to reduce PM2.5 levels in inland of the Korean Peninsula.