Practical usefulness of observing the free tropospheric acidic gases with a parallel plate wet denuder coupled ion chromatograph

Mountain observatories at high altitudes, far from local anthropogenic emission sources, are considered ideal for monitoring temporal variations of tropospheric air pollutants. During August 17–21 in 2013, we measured sulfur dioxide and nitric acid concentrations in the free troposphere at the top (3776 m a.s.l.) of Mt. Fuji, Japan. A parallel plate wet denuder-ion chromatographic system was used for the online measurement with 15 min temporal resolution. The continuous observations were successfully achieved without any problems. Of the samples collected, 97.8% of sulfur dioxide and 75.7% of nitric acid were above the limits of quantification. The average gas concentrations ± standard deviation (n = 408) were 0.106 ± 0.377 ppbv for sulfur dioxide and 0.015 ± 0.014 ppbv for nitric acid, respectively. Episodic elevations of sulfur dioxide concentration were recorded from August 20 to 21. Backward trajectory analyses indicated that the high-temporal resolution monitor detected the volcanic sulfur dioxide from Mt. Sakurajima, located 857 km from the sampling point. High-time-resolved observations in the free troposphere proved useful for source identification of air pollutants.