Development of method for measuring concentrations of gaseous and particulate formic acid in indoor air

In modem living environments, humans are exposed to numerous types of pollutants in indoor air. However, secondary emission products generated through chemical reactions have not been fully concerned in relation to so-called Sick House Syndrome. In this study, we focused on formic acid suspected to have impact on human health such as chemical sensitivity due to its low irritant level. Gas to particle conversion is a possible way of decay of gaseous formic acid in indoor air due to lower vapor pressure of formate. Then, authors have developed a sampling apparatus, by serially connecting miniature diffusion scrubber, impinger and air pump, for the determination of gas-particle distribution of formic acid in indoor air. Ion chromatography was employed for the analysis of formate ion trapped in the aqueous potassium hydroxide in each sampling device. The collection efficiency of the gaseous formic acid by the first stage scrubber was 94% without back-diffusion of trapped formic acid and sink of particles in the scrubber. Collection amount of formate species by this system was equivalent to that by a previous impinger method. Field measurements were conducted at occupied houses. The results showed the formic acid was firstly generated as gaseous form and gradually changed to particulate form with time in indoor air of the houses. However, the conversion mechanism was still unknown, because the gas-particle ratio was not consistent by the day even in the same house.