Shipboard Observations of Aerosol Chemical Properties Over the Western Pacific Ocean in Winter 2018

Based on a shipboard observation conducted in winter 2018, we reported the aerosol chemical properties and their differences in offshore and remote oceans over the Western Pacific Ocean (WPO). It's found that the chemical compositions over the WPO have significant spatial heterogeneity due to the influences of regional transport of anthropogenic aerosols and long-path transport of dust aerosols. The average concentration of water soluble ions during the whole sampling period followed Cl- > OC > Na+ > SO42- > NO3- > Ca2+ > Mg2+ > EC > K+ > NH4+. Crustal elements of Ca (980.41 ng/m(3)), Na (971.55 ng/m(3)), and Al (781.16 ng/m(3)) were uniformly distributed in offshore area, but high proportion of Na elements dominated in remote regions. The total concentration of heavy metals including Zn, Cu, Cr, Pb and others originating from anthropogenic sources were 208 ng/m(3) along the coastal region, about 10 times higher than that of 20.2 ng/m(3) in the offshore and remote seas. For the reconstructed components, we found an increase of sea-salt aerosol ranged from 3% to 72%, and a decrease of black carbon, organic matter and secondary inorganic salts, indicating a transformation from anthropogenic influence to marine environment. The rapidly increased secondary organic matter during dust event revealed that the transport of dust serves as catalysts to promote multi-phase reactions. Cl- photochemical reaction rate in offshore area was mainly affected by sulfate from anthropogenic emissions, with an average chlorine loss rate of 18%, whereas it was inverse Cl- excess in the remote oceans.