Indoor/outdoor relationships of airborne ionic substances: Comparison of electronic equipment room and factory environments

In previous work, the indoor and outdoor airborne concentrations and indoor surface accumulation rates of ionic substances contained in fine (<2.5) and coarse (2.5–15 μm) particles were determined for low-occupancy electronic equipment rooms. This work has now been extended to an electronic equipment manufacturing environment.Comparison of indoor and outdoor concentrations at the manufacturing facility for both fine and coarse particles show substantially different behavior from that seen for the electronic equipment rooms.As was found previously, the dominant species in fine particles are ammonium and sulfate, which closely track each other. Their indoor and outdoor concentrations also track, but the indoor/outdoor ratios are larger by a factor of 4–5 than those found for the electronic equipment rooms. Sodium shows tracking behavior similar to ammonium and sulfate and its indoor/outdoor ratio is also large. Other ions in fine particles show elevated indoor/outdoor ratios for some sampling intervals and tracking is not evident, thought it may be masked by the large fractional error associated with species with low concentrations. There is no dominant species in the coarse fraction. Sodium and chloride track each other strongly indoors and outdoors and the indoor and outdoor concentrations of each track closely. Potassium, as well as chloride, exhibit indoor/outdoor ratios that are sometimes much larger than 1.Modelling of indoor/outdoor relationships using a mass-balance model has shown that indoor concentrations can be accurately predicted from outdoor concentrations for species with no indoor sources. The model also shows that the source generation rates for fine and coarse particles indoors range from 0 to 6.6 and 2.3 to 5.8 mg min^?1, respectively, for a room with a volume of 6336m³.