Chemical nature of PM_2.5 and PM₁₀ in the coastal urban Xiamen, China: Insights into the impacts of shipping emissions and health risk

With objective of estimating the impact of ship emissions on ambient PM_2.5 and PM₁₀ levels and human health at a coastal urban site in Xiamen Island, a one year long sampling campaign was carried out from January 2017 to January 2018. Samples were subject to chemical analysis for various chemical components including water-soluble inorganic ions, carbonaceous species, and elements. The annual average PM_2.5 and PM₁₀ mass concentrations were, respectively, 32.8 ± 18.9 μg m⁻³ and 54.5 ± 29.6 μg m⁻³. The highest seasonal average concentrations were found in winter-spring and the lowest in summer due to the seasonal monsoon and gas-particle conversion. The rapid accumulation of vehicle exhaust and the stable existence of NH₄NO₃ in the ground layer within the urban area contributed to the incremental PM. Sulfate, nitrate, ammonium and organic carbon in PM_2.5 have decreased since 2011–2013, while elemental carbon increased significantly. This suggests that the motor vehicle and/or ship emissions contributions to PM_2.5 have increased relative to coal combustion over the past five years. The temporal variations of PM and its associated components during the BRICS summit control period further confirmed the important role of traffic related emissions in PM mass. Primary particulates resolved by PMF analysis plus secondary sulfate derived from secondary sulfate formation were estimated to account for 7.56% and 8.31% of PM_2.5 and PM₁₀, respectively. Selected heavy metals (As, Cd, Ni, V, Mn, hexavalent Cr, Ba and Pb) originating from ship emissions contributed 64.4% for PM_2.5 and 53.2% for PM₁₀ of the total non-cancer risk. Carcinogenic risk (lifetime cancer risk) for ship emissions associated with these hazard metals accounted for 50.6% for PM_2.5 and 44.5% for PM₁₀. Therefore, control measures applied to the ship emissions can benefit the local air quality improvement and reduce health burden to people around the port.