Chemical Form and Behavior of Arsenic Compounds in the Atmosphere

The concentrations of arsenic compounds in the atmosphere at trace levels were measured at various sites in Japan. The particulate arsenic was collected by two stage Andersen impactor, and the gaseous arsenic was collected by a filter impregnated with 10% poly(ethyleneimine) and glycerol solution. Arsenic compounds were analyzed by hydride generation atomic absorption spectrophotometry combined with a cold trap of liquid nitrogen for a trapping of arsines. This method has a high sensitivity and can determine organic and inorganic arsenic compounds separately. It was concluded that more than 90% of arsenic in the atmosphere was inorganic particulate arsenic (0.38~9.7 ng As/m3), the rest were organic particulate arsenic (0.03~0.27 ng As/m3) and inorganic gaseous arsenic (0.006~0.09 ng As/m3). Most of the organic arsenic was dimethylarsinic acid (DMAA). Methylarsonic acid (MAA) and trimethylarsine (TMA) were not found in any sample. Organic gaseous arsenic was not found either. Atmospheric concentration of organic arsenic (DMAA) increased in summer and decreased in winter. However, as for inorganic arsenic and gaseous arsenic, seasonal variation was not observed. Thus production of organic arsenic might be due to the methylation of inorganic arsenic through biological processes. Size distribution of inorganic arsenic in the atmosphere was bimodal with two concentration peaks at 2 ¼m. and 0.5¼m, and its mass medean aerodynamic diameter (MMAD) was 1.0¼m and most of inorganic arsenic existed as fine particles with diameters less than 2 ¼m. Size distribution of organic arsenic was quite predominant in fine particle with a concentration peak at 0.5 ¼m, and organic arsenic was not detected at coarse particle region exceeding 4¼m. It is considered that inorganic and organic arsenic compounds are emitted as gas to the air by burning oil and coal and by methylation of inorganic arsenic, and then condense to fine particles. Therefore, it suggests that size distributions of inorganic and organic arsenic in the atmosphere are mainly in fine particle.