10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Indoor PM2.5 in an Urban Zone with Heavy Wood Smoke Pollution: The Case of Temuco, Chile
HECTOR JORQUERA, Lupita Montoya, Francisco Barraza, Pontificia Universidad Catolica de Chile
Abstract Number: 770 Working Group: Indoor Aerosols
Abstract Temuco (38°44’ S, 72°36’ W)) is a mid-size city in southern Chile (south of 35° S) with severe ambient air pollution from wood smoke; however, little is known about indoor air quality there. A measurement campaign at 63 households in the Temuco urban area was conducted in winter 2014. Indoor and outdoor (24-hr) PM2.5 and its elemental composition were measured and compared. Infiltration parameters and outdoor/indoor contributions to indoor PM2.5 were also determined. A statistical evaluation of how various air quality interventions and household features influence indoor PM2.5 was also performed. Air sampling was performed at each household only on workdays (Monday through Thursday) for 24 h. A Minivol sampler (TAS, Airmetrics, Eugene, OR, USA, 5 L/min) was installed in each household to collect PM2.5 on a Teflon filter (46.2 mm, PTFE, Whatman, NJ, USA). Simultaneously, outdoor PM2.5 levels were measured at a single outdoor site using an ambient PM2.5 sampler (Partisol 2000i, Thermos, US, 16.7 L/min). Elemental analysis of indoor/outdoor filters by XRF was carried out at ChesterLab (OR, USA). A survey completed by each head of household included questions about household features such as number and type of cookstoves and heaters, whether the household had undergone a weatherization process and presence of pets or smokers.
Median indoor and outdoor PM2.5 concentrations were 44.4 and 41.8 μg/m3, respectively. An average infiltration factor (0.62 ± 0.06) was estimated using S as a tracer species. Using a simple mass balance approach, median indoor and outdoor contributions to indoor PM2.5 concentrations were then estimated as 12.5 and 26.5 μg/m3, respectively. Therefore, 68% of indoor PM2.5 comes from outdoor infiltration. This high percentage is due to high outdoor pollution and relatively high household air exchange rates (median: 1.06 h-1).
This study found that S, Br and Rb were dominated by outdoor contributions, while Si, Ca, Ti, Fe and As originated from indoor sources. Using continuous indoor and outdoor PM2.5 measurements, a median indoor source strength of 75 μg PM2.5/min was estimated for the diurnal period, similar to literature results. In the evening period, the median estimate was 135 μg PM2.5/min, reflecting a more intense wood burning at night.
Significant (α=0.10) effects of current interventions and household characteristics on indoor air quality were also found. Concentrations in households heated with woodstoves only were higher than those in households that used a mix of heating fuels, supporting the ongoing woodstove changeout program. Weatherized households reduced the infiltration of species of outdoor origin like S, supporting the ongoing subsidized weatherization program; however, indoor PM2.5 was not significantly lower in those households, likely due to indoor PM2.5 sources offsetting the reduced outdoor infiltration. In households where wood cookstoves were used, indoor PM2.5 concentrations were higher than in households using LPG cookstoves, suggesting that a cookstove improvement program may help decrease indoor PM2.5. Indoor PM2.5 concentrations in smaller subsidized households tended to be higher than in larger dwellings, reflecting an environmental justice issue that needs to be investigated. Overall, this study presents evidence of a complex indoor/outdoor air quality challenge in Temuco — and in southern Chile as well — requiring a continued and diversified management approach. Further, the ongoing slow decrease in outdoor levels means that improving indoor PM2.5 in Temuco through ongoing air quality management policies will likely require an extended period of time.