conference paper
published journal article
published journal article
This paper proposes a hybrid approach to model usage at public bikeshare system (PBS) stations. The proposed Cluster Stations and Regress (CSR) modeling approach involves first clustering PBS stations based on the types of trips they attract using k-means or fuzzy c-means clustering techniques. After obtaining station-cluster membership values for each station, the authors estimate multilevel mixed-effect regression models with interactions between the station-cluster membership variables and determinants of PBS station usage. Determinants considered in the empirical models include the socio-demographic and commute characteristics of the residents in each PBS stationâ??s census tract, weather variables, temporal variables, and PBS station proximity to restaurants, jobs, transit stops, rail stations, the central business district (CBD), bicycle infrastructure, and other PBS stations. The model results clearly indicate that determinants of PBS station usage vary across station-clusters and including station-cluster interaction terms significantly improves model fit. Additionally, the results of cross-validation tests indicate that the CSR approach is a promising method to model monthly PBS station usage. The empirical results also clear up conflicting findings in the literature in terms of the impact of nearby PBS stations on station usage. The authors find that station usage increases with the number of other PBS stations within 1â??5â?¯km for member trips. However, after controlling for this effect, station usage decreases as the number of other PBS stations within 0.8â?¯km increases.
published journal article
In recent years, wildfires in California have increased in frequency and intensity due to climate change and prolonged drought. The air pollutants released by wildfires cause significant health consequences, among which polycyclic aromatic hydrocarbons (PAHs) are particularly toxic. Estimating PAH emissions from wildfires is challenging due to variability in vegetation types. In this study, we estimate PAH emission rates across California at a high resolution, based on laboratory-measured PAH emission rates from 22 different vegetation types and detailed vegetation mapping. By combining these estimates with biomass burning data from the NCAR Fire Inventory, the Community Multiscale Air Quality Modeling System simulates PAH concentrations for the 2017 fire season. The modeling results compare favorably to measurements from three PAH monitoring sites in California. The peak PAH emissions from wildfire events are up to be 80 times higher in the gas phase and 32 times higher in the particle phase compared to a case without fire emissions. The population-weighted PAH concentrations from the fire case (0.053 µg/m3) are 47 % higher compared to a non-fire case (0.036 µg/m3) in the particle phase and 11 % higher in the gas phase (9.82 ppt compared to 8.83 ppt) during the study period. While highly depended on the meteorological condition, the simulated spatial distribution indicates that gas-phase PAHs are less likely to travel long distances from the fire source and are prone to aging into the particle phase during transport. Consequently, populations are more likely to be exposed to particle-phase PAHs during wildfire events. This finding has important implications for understanding the health impacts of wildfire-induced PAH concentrations, as particle-phase PAHs may have different toxicological effects compared to gas-phase PAHs.
published journal article
published journal article
published journal article
published journal article
PM2.5 is an air contaminant that has been widely associated with adverse respiratory and cardiovascular health, leading to increased hospital admissions and mortality. Following concerns reported by workers at an industrial facility located in Santa Ana, California, workers and community leaders collaborated with experts in the development of an air monitoring pilot study to measure PM2.5 concentrations to which employees and local residents are exposed during factory operating hours. To detect PM2.5, participants wore government-validated AtmoTube Pro personal air monitoring devices during three separate workdays (5 AM–1:30 PM) in August 2021. Results demonstrated a mean PM2.5 level inside the facility of 112.3 µg/m3, nearly seven-times greater than outdoors (17.3 µg/m3). Of the eight workers who wore personal indoor sampling devices, five showed measurements over 100 μg/m3. Welding-related activity inside the facility resulted in the greatest PM2.5 concentrations. This study demonstrates the utility of using low-cost air quality sensors combined with employee knowledge and participation for the investigation of workplace air pollution exposure as well as facilitation of greater health-related awareness, education, and empowerment among workers and community members. Results also underscore the need for basic measures of indoor air pollution control paired with ongoing air monitoring within the Santa Ana facility, and the importance of future air monitoring studies aimed at industrial facilities.
published journal article
published journal article
Mobility is one mechanism used to address the federal goals of deconcentrating poverty and minorities. The Housing Choice Voucher Program relies on participants to make residential location decisions consistent with these goals. Our research investigates the level and impact of mobility on the neighborhood quality of voucher holders, their neighborhood conditions by race and ethnicity, and perceived obstacles to mobility within the jurisdiction of a Southern California housing authority. About one-third of the sample moved during the study, and moving resulted in improved neighborhoods for only one subset of movers. Minorities live in more impoverished, overcrowded neighborhoods than nonminorities, even when controlling for mobility status, contract rent, and other factors. Further, most voucher holders see the lack of rental units as a major obstacle to mobility. These findings suggest that current policy is not uniformly achieving deconcentration and that real and perceived barriers to mobility exist, especially for minorities.