Local formation of sulfates contributes to the urban haze with regional transport origin

Urban particle pollution is affected by not only the emissions of pollutants and secondary aerosol formation through atmospheric chemistry on a local scale, but also the regional transport of particles and precursor gases from highly polluted upwind areas. However, this regional impact on urban particle formation is not well understood. Wintertime haze events occur at Seoul, Korea through the combination of regional transport from China and local formation at Seoul. We perform thermodynamic model simulations based on inorganic component measurements of haze particles collected at Seoul and Deokjeok Island (upwind background). Results suggest that in the downwind area (Seoul) the local formation of sulfates increases the mass concentrations of transported particles through the gas-particle partitioning of semivolatile nitric acid (HNO3) and ammonia (NH3). Therefore, this synergetic effect of the local sulfate formation on urban haze with regional transport must be considered in implementing effective particle reduction controls for urban sustainability.