Abstract
The average collection efficiency of gaseous nitric acid (HNO3(g)) at the Cape Hedo Aerosol and Atmosphere Monitoring Station (CHAAMS), Okinawa, Japan, by an annular denuder method from March 2008 to April 2009 decreased by approximately 20% when compared to that experimentally obtained (~100%). We investigated the causes by which the collection efficiency decreased during the long-term sampling in the marine atmosphere. We experimentally investigated the removal of nitric acid collected from the inner surface of the denuder during the long-term sampling, and it was found that part of the nitric acid collected on the surface of the denuder was removed. However, the experimental result showed that the decrease in the collection efficiency was only 3% on average. We also analyzed the factor in the decreasing collection efficiency using the monitoring data at the CHAAMS. Sea salt particles could be related to the decrease in the collection efficiency. In order to investigate the detailed mechanisms, an intercomparison between the HNO3(g) concentrations measured by the annular denuder method and a filter pack method by the Acid Deposition Monitoring Network in East Asia was conducted. This result might suggest that the annular denuder method overestimates the HNO3(g) concentrations and might support the fact that the uptake of the particulate nitrate on the inner surface of the annular denuder causes the decrease in the collection efficiency.
