Due to the global response to the COVID-19 pandemic, there have been a variety of policy responses that have produced a range of expected and unexpected effects on society and our surrounding environment. One widely reported result of the pandemic response is that travel restrictions have resulted in improvements in regional air quality. This study aims to determine the effect of COVID-19 related Stay at Home precautions on air quality in a metropolitan area. We specifically focus on CO, NO2, and PM10 in Maricopa County (Phoenix), Arizona, as these all contribute to local air quality concerns. The role of meteorological parameters on ambient concentrations for these pollutants was investigated by using the local planetary boundary layer height (PBH) to account for vertical mixing. Across all three sites studied, there was no uniform decrease in either CO or NO2, even when freeway traffic volume was down by ~35%. For PM10, there was a significant decrease of ~45% seen at all the sites for the period most directly impacted by local Stay at Home restrictions compared to the past two years. This indicates that different pollutants have fundamentally different behavior in the local environment and suggests that these pollutants originate from different sources.

Valley fever is a lung infection caused by the inhalation of infectious spores from the fungus Coccidioides spp. Coccidioides is a genus of soil dwelling fungi endemic to the arid regions of the southwestern United States, Mexico, and Central and South America. Few Valley fever studies have focused on detecting Coccidioides spores in airborne respirable particles, which is the primary infection vector. This study looks at the presence of Coccidioides in air at a highly soil positive site in Mesa, Arizona. Aerosol samples were collected for 24 h every 6 days, following the Environmental Protection Agency sampling schedule. Meteorological data were collected from a nearby weather station. Coccidioides were detected in ∼68% of the aerosol samples. Bulk PM10 did not have a statistically significant relationship with presence of Coccidioides; however, there was a significant relationship between the amount of crustal material in the aerosols and presence of Coccidioides. Previous studies link the presence of Coccidioides in air with bulk PM10 concentrations; however, we found that bulk PM10 concentrations give an incomplete story. Additionally, there were statistically significant relationships with the presence of Coccidioides and meteorological parameters, including relative humidity, temperature, and wind speed. This study emphasizes the importance of dust entrainment in the transmission of Coccidioides.

With the goal of corroborating existing emissions inventories of volatile organic compounds (VOCs), a statistical analysis was undertaken on measured ambient VOC concentrations in Maricopa County, Arizona. The Chemical Mass Balance (CMB) model was used to generate emissions source contribution estimates based on ambient VOC concentrations collected at the JLG Supersite in Phoenix, Arizona, and emissions source profiles obtained from EPA's SPECIATE database. With trial-and-error, optimal model performance using a combination of emissions source profiles yielded source contribution estimates which could be compared to existing regulatory engineering-based emissions inventories. The ultimate objective of this study is to offer a comparison to the "top-down" emissions modeling via CMB and the "bottom-up" modeling traditionally used in preparing emission inventories to identify possible discrepancies and help direct future investigations to better understand local air quality. The methods used to develop the "bottom-up" inventory rely upon sound modeling developed to accurately capture emissions from various source categories. The results show discrepancies between the "bottom-up" and "top-down" emission inventory for VOC emissions from biogenic and natural gas combustion sources, suggesting that the emission strength from these source categories should be further investigated.Implications: The following implication statement has been prepared for the manuscript titled Source Apportionment of Measured Volatile Organic Compounds in Maricopa County, Arizona. The purpose of preparing such a study was to independently corroborate the findings of Maricopa County Air Quality Department (MCAQD) on source contribution estimates of VOC emissions as published in their 2020 Periodic Emissions Inventory for Ozone Precursors. The goal of preparing the findings in the study was to provide additional commentary on the significance of various VOC emissions sources to tropospheric ozone formation in Maricopa County through an alternate air quality modeling approach. The findings from this study are significant to the environment and health of Maricopa County as they offer additional insights into the pathways by which tropospheric ozone may form.

Active travelers face co-occurring environmental hazards and optimizing routes to minimize a singular hazard (heat or particulate matter (PM₁₀)) can inadvertently worsen the other. We deploy Icarus, a routing framework that accumulates spatiotemporally resolved multi-hazard exposure to identify least-exposed paths, on 287,096 walking trips in metropolitan Phoenix. Evaluating cross-hazard outcomes under single-objective exposure minimization, we introduce a budget-constrained multi-objective routing approach to manage resulting trade-offs. Heat-minimized routing increases mean PM₁0 exposure in 73% of rerouted trips, while PM₁₀-minimized routing raises heat exposure in 35% of trips. ”Risk-pockets” for secondary penalties concentrate in high-baseline-exposure trips. A three-axis adaptive budget framework combining primary urgency, secondary damage severity, and Pareto efficiency limits deterioration in the non-prioritized hazard while retaining 90–93% of primary benefit, confirmed statistically equivalent to single-objective outcomes via two one-sided tests. The framework supports configurable conservative and aggressive enforcement modes, making multi-hazard routing trade-offs auditable and policy responsive.