Keywords: ammonium ion, chloride ion, indoor and outdoor concentrations, nitrate ion, particle size, sulfate ion, suspended particulate matter, pollution
Indoor-outdoor relationship of suspended particulate matter and its chemical composition at different sizes
The indoor-outdoor concentration relationship of particulate matter PM9.0 (aerodynamic diameter 9 µm or smaller) and its chemical composition (sulfate, nitrate, chloride and ammonium) has been studied. Samples were collected using four identical Anderson impactors, each one collecting nine size ranges by eight impactor stages (9, 5.8, 4.7, 3.3, 2.1, 1.1, 0.65 and 0.43 µm) plus a back-up filter representing particles finer than 0.45 µm. Concentrations of sulfate, nitrate and chloride were determined by ion chromatography, and an ammonium-selective ion electrode plus a Corning pH ion meter were used to determine ammonium ion. The results revealed that sulfate was the predominant component and chloride the least abundant. The size distribution of sulfate, nitrate and ammonium very strongly peaked near 0.65 µm and with very little at the larger sizes. The chloride concentration was depleted in the fine particles and enhanced in the relatively coarser particles, with the peak at 3.3 µm. All these concentrations had a significant linear relationship with mass concentrations in outdoor samples. In indoor samples, the same relation was observed only for sulfate and ammonium, which were also significantly correlated with each other. Furthermore, indoor sulfate, chloride and ammonium concentrations were higher towards the finest particle sizes, indicating a higher potential inhalation health hazard. The study also confirmed that indoor air quality depends on outdoor atmospheric pollution level, indoor activities and virtually on the particle size. Finally, the study would assist in selecting the type of collector required to reduce the level of particulates to an acceptable level for indoor ambient air.