Atmospheric concentrations of nitric acid, sulfur dioxide, particulate nitrate and particulate sulfate, and estimation of their dry deposition on the urban- and mountain-facing sides of Mt. Gokurakuji, Western Japan

Atmospheric concentrations of nitric acid (HNO3), sulfur dioxide (SO2), particulate nitrate \( {\left( {{\text{NO}}^{ - }_{3} } \right)} \) and particulate sulfate \( {\left( {{\text{SO}}^{{2 - }}_{4} } \right)} \) on the urban- and mountain-facing sides of Mt. Gokurakuji were measured from November 2002 to October 2003, in order to evaluate the effects of anthropogenic activity on air quality and dry deposited nitrate and sulfate on the surfaces of pine foliage. The results showed that HNO3, SO2 and \( {\text{NO}}^{ - }_{3} \) concentrations were significantly higher (P < 0.05) on the urban-facing side (1.54, 2.48 and 0.65 μg m−3, respectively) than the mountain-facing side (0.67, 1.19 and 0.37 μg m−3, respectively), while \( {\text{SO}}^{{2 - }}_{4} \) concentrations did not differ significantly between the two sides (urban-facing: 2.80 μg m−3; mountain−facing: 2.05 μg m−3). Indirect estimates of dry deposition rates of nitrate and sulfate to the surfaces of pine foliage based on the measured concentrations approximately agreed with the measured values determined by the foliar rinsing technique in a previous study. It was found that HNO3 was the major source (approximately 80%) of dry deposited nitrate on pine foliage, while the contribution from \( {\text{SO}}^{{2 - }}_{4} \) was about equal to that from SO2. In conclusion, HNO3 and SO2 appear to be dominant species reflecting higher dry deposition rates of nitrate and sulfate on the urban-facing side compared to the mountain-facing side of Mt. Gokurakuji.