Indoor PM2.5 in an urban zone with heavy wood smoke pollution: The case of Temuco, Chile.

Temuco is a mid-size city representative of severe wood smoke pollution in southern Chile; however, little is known about the indoor air quality in this region. A field measurement campaign at 63 households in the Temuco urban area was conducted in winter 2014 and is reported here. In this study, 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. This study determined median indoor and outdoor PM2.5 concentrations of 44.4 and 41.8 µg/m3, respectively. An average infiltration factor (0.62 ±â€¯0.06) was estimated using sulfur 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. For the evening period, the median estimate rose to 135 µg PM2.5/min, reflecting a more intense wood burning associated to cooking and space heating at night. Statistical test results (at the 90% confidence level) support the ongoing woodstove replacement program (reducing emissions) and household weatherization subsidies (reducing heating demand) for improving indoor air quality in southern Chile, and suggest that a cookstove improvement program might be helpful as well.

Short-term dynamics of indoor and outdoor endotoxin exposure: Case of Santiago, Chile, 2012.

Indoor and outdoor endotoxin in PM2.5 was measured for the very first time in Santiago, Chile, in spring 2012. Average endotoxin concentrations were 0.099 and 0.094 [EU/m(3)] for indoor (N=44) and outdoor (N=41) samples, respectively; the indoor-outdoor correlation (log-transformed concentrations) was low: R=-0.06, 95% CI: (-0.35 to 0.24), likely owing to outdoor spatial variability. A linear regression model explained 68% of variability in outdoor endotoxins, using as predictors elemental carbon (a proxy of traffic emissions), chlorine (a tracer of marine air masses reaching the city) and relative humidity (a modulator of surface emissions of dust, vegetation and garbage debris). In this study, for the first time a potential source contribution function (PSCF) was applied to outdoor endotoxin measurements. Wind trajectory analysis identified upwind agricultural sources as contributors to the short-term, outdoor endotoxin variability. Our results confirm an association between combustion particles from traffic and outdoor endotoxin concentrations. For indoor endotoxins, a predictive model was developed but it only explained 44% of endotoxin variability; the significant predictors were tracers of indoor PM2.5 dust (Si, Ca), number of external windows and number of hours with internal doors open. Results suggest that short-term indoor endotoxin variability may be driven by household dust/garbage production and handling. This would explain the modest predictive performance of published models that use answers to household surveys as predictors. One feasible alternative is to increase the sampling period so that household features would arise as significant predictors of long-term airborne endotoxin levels.

Effects of temperature and resource variation on insect population dynamics: the bordered plant bug as a case study.

In species with complex life cycles, population dynamics result from a combination of intrinsic cycles arising from delays in the operation of negative density-dependent processes (e.g., intraspecific competition) and extrinsic fluctuations arising from seasonal variation in the abiotic environment. Abiotic variation can affect species directly through their life history traits and indirectly by modulating the species' interactions with resources or natural enemies.We investigate how the interplay between density-dependent dynamics and abiotic variability affects population dynamics of the bordered plant bug (Largus californicus), a Hemipteran herbivore inhabiting the California coastal sage scrub community. Field data show a striking pattern in abundance: adults are extremely abundant or nearly absent during certain periods of the year, leading us to predict that seasonal forcing plays a role in driving observed dynamics.We develop a stage-structured population model with variable developmental delays, in which fecundity is affected by both intra-specific competition and temporal variation in resource availability and all life history traits (reproduction, development, mortality) are temperature-dependent. We parameterize the model with experimental data on temperature-responses of life history and competitive traits and validate the model with independent field census data.We find that intra-specific competition is strongest at temperatures optimal for reproduction, which theory predicts leads to more complex population dynamics. Our model predicts that while temperature or resource variability interact with development-induced delays in self-limitation to generate population fluctuations, it is the interplay between all three factors that drive the observed dynamics. Considering how multiple abiotic factors interact with density-dependent processes is important both for understanding how species persist in variable environments and predicting species' responses to perturbations in their typical environment.