Quantifying fine particle emission events from time-resolved measurements: Method description and application to 18 California low-income apartments.

PM2.5 exposure is associated with significant health risk. Exposures in homes derive from both outdoor and indoor sources, with emissions occurring primarily in discrete events. Data on emission event magnitudes and schedules are needed to support simulation-based studies of exposures and mitigations. This study applied an identification and characterization algorithm to quantify time-resolved PM2.5 emission events from data collected during 224 days of monitoring in 18 California apartments with low-income residents. We identified and characterized 836 distinct events with median and mean values of 12 and 30 mg emitted mass, 16 and 23 minutes emission duration, 37 and 103 mg/h emission rates, and pseudo-first-order decay rates of 1.3 and 2.0/h. Mean event-averaged concentrations calculated using the determined event characteristics agreed to within 6% of measured values for 14 of the apartments. There were variations in event schedules and emitted mass across homes, with few events overnight and most emissions occurring during late afternoons and evenings. Event characteristics were similar during weekdays and weekends. Emitted mass was positively correlated with number of residents (Spearman coefficient, ρ=.10), bedrooms (ρ=.08), house volume (ρ=.29), and indoor-outdoor CO2 difference (ρ=.27). The event schedules can be used in probabilistic modeling of PM2.5 in low-income apartments.

Hazard assessment of chemical air contaminants measured in residences.

UNLABELLED: Identifying air pollutants that pose a potential hazard indoors can facilitate exposure mitigation. In this study, we compiled summary results from 77 published studies reporting measurements of chemical pollutants in residences in the United States and in countries with similar lifestyles. These data were used to calculate representative mid-range and upper-bound concentrations relevant to chronic exposures for 267 pollutants and representative peak concentrations relevant to acute exposures for five activity-associated pollutants. Representative concentrations are compared to available chronic and acute health standards for 97 pollutants. Fifteen pollutants appear to exceed chronic health standards in a large fraction of homes. Nine other pollutants are identified as potential chronic health hazards in a substantial minority of homes, and an additional nine are identified as potential hazards in a very small percentage of homes. Nine pollutants are identified as priority hazards based on the robustness of measured concentration data and the fraction of residences that appear to be impacted: acetaldehyde; acrolein; benzene; 1,3-butadiene; 1,4-dichlorobenzene; formaldehyde; naphthalene; nitrogen dioxide; and PM(2.5). Activity-based emissions are shown to pose potential acute health hazards for PM(2.5), formaldehyde, CO, chloroform, and NO(2). PRACTICAL IMPLICATIONS: This analysis identifies key chemical contaminants of concern in residential indoor air using a comprehensive and consistent hazard-evaluation protocol. The identification of a succinct group of chemical hazards in indoor air will allow for successful risk ranking and mitigation prioritization for the indoor residential environment. This work also indicates some common household activities that may lead to the acute levels of pollutant exposure and identifies hazardous chemicals for priority removal from consumer products and home furnishings.