Characteristics of atmospheric depositions of ionic and carbonaceous components at remote sites in Japan

Abstract:

Atmospheric deposition process is important to evaluate lifetimes and budget of atmospheric components. Deposition amounts of sulfur and nitrogen compounds have been evaluated not only in East Asian region but also worldwide. On the other hand, atmospheric deposition of carbonaceous components including organic carbon (OC), elementary carbon (EC) and Polycyclic Aromatic Hydrocarbons (PAHs) were monitored only at a few sites in Europe, North America and Africa, which will obscure removal process and atmospheric concentration distribution of those components. In this study, ionic and carbonaceous components in precipitation and aerosol are monitored at remote sites in Japan, and the characteristics of atmospheric deposition amounts were evaluated.Field observations have been implemented at the Noto station since November 2013 and the Sado station since May 2011. Wet deposition samples were collected by rain samplers, and dry deposition samples were collected by high volume or low volume aerosol samplers. Concentrations of Cl^-, NO₃^-, SO₄^2-, NH₄⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺ were measured by ion chromatography, EC and OC by the IMPROVE protocol, and PAHs by HPLC with a fluorescence detector. Wet deposition amounts were calculated as the products of aqueous concentration and precipitation amounts, and dry deposition amounts were as the products of aerosol concentrations and deposition velocity estimated by the Inferential Method.Total (wet and dry) annual deposition amounts of carbonaceous components of NO₃^-, SO₄^2-, EC, water insoluble OC, Fluoranthene at Noto (Nov. 2013 to Oct. 2014) were 4353.81 mg/m², 7020.50 mg/m², 149.84 mg/m², 1191.09 mg/m², 28.6 μg/m², respectively. These amounts are comparable total annual deposition amounts of OC and EC at Sado (May 2011 to Feb. 2012), which were 166.04 mg/m² and 834.0 mg/m². Higher deposition amounts of ionic and carbonaceous components were observed, which would be attributable to long range transportation of the East Asian continent.