Despite increasing evidence that airborne polycyclic aromatic hydrocarbon (PAH) exposures contribute to adverse health outcomes for sensitive populations, limited data are available on short-term intraurban spatial distributions for use in epidemiologic research. Exposure assessments for airborne PAHs are uncommon because air sampling for PAHs is a labor-, equipment-, and time-intensive task. To address this gap we measured wintertime PAH concentrations during 2010-2011 in Bakersfield, California, USA, a major city in the Southern San Joaquin Valley. Specifically, 58 96-hour integrated PAH samples were collected during 4 time periods at 14 locations from November 2010 to January 2011; duplicates were collected at two sites. We also collected elemental carbon (EC) at the same 14 sites and analyzed the two time periods with the highest ambient PAH pollution. We used linear regression models to quantify the relationship between potential spatial and temporal predictors of PAH concentrations. We found that wintertime PAH concentrations in Bakersfield, CA, are best predicted by meteorological variables and traffic proximity. Our model explains a moderate amount of the variability in the data (R²=0.58), likely reflecting the major sources of PAHs in Bakersfield. We also observed that PAH concentrations were more spatially variable than EC concentrations. Comparing our data to historical monitoring data at one location in Bakersfield showed that the relatively low PAH concentrations during the 2010-2011 winter in Bakersfield is part of a long-term trend in decreasing PAH concentrations.

As part of our ongoing research to understand the impact of polycyclic aromatic hydrocarbon (PAH) exposures on health in the San Joaquin Valley, we evaluated airborne PAH concentration data collected over 19 years (2000-2019) at the central air monitoring site in Fresno, California. We found a dramatic decline in outdoor airborne PAH concentrations between 2000 and 2004 that has been maintained through 2019. This decline was present in both the continuous particle-bound PAHs and the filter-based individual PAHs. The decline was more extreme when restricted to winter concentrations. Annual mean PAHs concentrations in 2017- 2018 of particle-bound PAHs were 6.8 ng/m³ or 62% lower than 2000 - 2001. The decline for winter concentrations of continuous particle-bound PAHs between winter 2019 and winter 2001 was 17.2 ng/m3, a drop of 70%. The 2001 to 2018 decline in average wintertime concentrations for filter-based individual PAHs was 82%. We examined industrial emissions, on-road vehicle emissions, residential wood burning, and agricultural and biomass waste burning as possible explanations. The major decline in PAHs from 2000-2004 was coincident with and most likely due to a similar decline in the amount of agricultural and biomass waste burned in Fresno and Madera Counties. On-road vehicle emissions and residential wood burning did not decline until after 2005. Industrial emissions were too low (2% of total) to explain such large decreases in PAH concentrations.

We assessed the efficacy of ozonation as an indoor remediation strategy by evaluating how a carpet serves as a sink and long-term source of thirdhand tobacco smoke (THS) while protecting contaminants absorbed in deep reservoirs by scavenging ozone. Specimens from unused carpet that was exposed to smoke in the lab ("fresh THS") and contaminated carpets retrieved from smokers' homes ("aged THS") were treated with 1000 ppb ozone in bench-scale tests. Nicotine was partially removed from fresh THS specimens by volatilization and oxidation, but it was not significantly eliminated from aged THS samples. By contrast, most of the 24 polycyclic aromatic hydrocarbons detected in both samples were partially removed by ozone. One of the home-aged carpets was installed in an 18 m³ room-sized chamber, where its nicotine emission rate was 950 ng day^-1 m^-2. In a typical home, such daily emissions could amount to a non-negligible fraction of the nicotine released by smoking one cigarette. The operation of a commercial ozone generator for a total duration of 156 min, reaching concentrations up to 10,000 ppb, did not significantly reduce the carpet nicotine loading (26-122 mg m^-2). Ozone reacted primarily with carpet fibers, rather than with THS, leading to short-term emissions of aldehydes and aerosol particles. Hence, by being absorbed deeply into carpet fibers, THS constituents can be partially shielded from ozonation.