Analysis of atmospheric deposition

   Under the GAW programme, JMA observed precipitation pH and ion concentrations as part of its monitoring of global-scale atmospheric pollution until 2020. The procedures for sampling, precipitation sample analysis and quality control of analytical values are in accordance with the stipulations of the Manual for the GAW Precipitation Chemistry Programme (WMO-GAW Report No. 160) .

   Daily precipitation samples are collected at Minamitorishima and sent to JMA Headquarters on a monthly basis for analysis. The analytical results are made public after undergoing a process of quality control.

Observation method

   Precipitation and dry deposition samples are collected using a ground-based sampling system (Figure 1) , and are picked up every day for precipitation and every month for dry deposition. Maximum wind speed and wind direction as well as precipitation amounts are recorded at the station.

Figure 1: Sampling system for precipitation and dry deposition

Analysis method

   Samples and meteorological records are sent on a monthly basis to JMA Headquarters, where pH, electrical conductivity, alkalinity and chemical composition are analyzed using a flow-cell pH meter, an electrical conductance meter, an automatic burette, an ion chromatograph and an atomic absorption spectrophotometer.

   Monthly mean values for precipitation are the weighted means of analytical results from daily samples based on daily precipitation amounts.

   Dry deposition samples are analyzed separately for water-soluble and water-insoluble components. For the former, chemical components are analyzed with residues distilled using an evaporator for weighing. For the latter, organic compounds are subjected to combustion for removal and the residual ashes are weighed. Monthly totals are determined for each component.

Table 1: Observation parameters of atmospheric deposition by JMA

Parameter		Precipitation	Dry deposition
pH		O
Electrocal Conductivity		O
Alkalinity		O
Chemical components	NH4+-N	O
	Na+	O	O
	K+	O	O
	Ca2+	O	O
	Mg2+	O	O
	Cl−	O	O
	NO2−-N	O	O
	NO3−-N	O	O
	SO42−-S	O	O
	Cd	O
	Hg	O