Smoking bans as particle source control and HVAC component loading due to airborne particle mass deposition
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This first part of this study assessed differences in the indoor air quality and occupancy levels in seventeen bars due to a city-wide smoking ban that took effect on September 1, 2005 in Austin, Texas, USA. The following were measured in each venue before and after the smoking ban: mean number of occupants, mean number of lit cigarettes, temperature, relative humidity, room volume, and PM2.5, CO, and CO2 concentrations. Additionally, VOC measurements were conducted at three of the venues. There was not a statistically significant change in occupancy, but the best estimate PM2.5 concentrations in the venues decreased 71 – 99%, a significant reduction in all venues, relative to the pre-ban levels; CO concentrations decreased significantly in all but one venue; and concentrations of VOCs known to be emitted from cigarettes decreased to below the detection limit for all but two common compounds. These results suggest that the smoking ban has effectively improved indoor air quality in Austin bars without an associated decrease in occupancy. The second part of this study modeled the amount of mass deposited on HVAC components for a month of operation (i.e., the loading rate) due to airborne particulate matter. The rate at which HVAC components load due to particle deposition is important from both an indoor air quality and energy perspective. The parameters that have the largest influence on the loading rates depend heavily on whether the building is residential or commercial. For the residential cases, the parameters that influenced the filter, coil, and supply-side duct loading rates the most were the Filtration and bypass, Coil properties, and Duct complexity parameters, respectively. For the commercial cases, which always employed some sort of intentional ventilation, the Ambient parameter was the most influential for all loading rates but the return-side ducts, for which the Emissions parameter was the most influential. Additionally, the Ambient and Emissions parameters ranked near the top of the most important parameters for many scenarios. For both the residential and commercial cases, the median over all cases for the filter loading rate was an order of magnitude larger than the median for the coil loading rate, which was an order of magnitude over the duct loading rates. The residential and commercial loading rates compare as follows: for median loading rates over all modeled scenarios, the commercial case for filter loading is approximately a factor of 89 over the residential case (65.39 versus 0.731 g/mo.); the commercial coil loading is approximately a factor of 39 over the residential case (1.83 versus 0.0468 g/mo.); and the commercial supply-side duct loading is approximately 114 times over the residential case (0.58 versus 0.0051 g/mo.). HVAC component loading causes higher pressure drops in the system, which can lead to reduced flow and reduced heating and cooling capacity for residential systems and increased fan energy usage for commercial systems. The results herein could be used to estimate filter changing and coil cleaning schedules with more information about how filter and coil loading affect pressure drop over time in real indoor environments. Additionally, the loading can have indoor air quality implications in the form of secondary pollutant formation or resuspension of biologically active material.