Real-time measurements with high spatial resolution were conducted using a pollution-free mobile monitoring platform (MP)—an electric vehicle equipped with fast-response instruments for particles and gases—on routes in the South Coast Air Basin. A series of novel findings resulted from our studies in West Los Angeles and Downtown Los Angeles, including Boyle Heights, and in communities adjacent to the Ports of Long Beach and Los Angeles in connection with the ARB-sponsored Harbor Communities Monitoring Study (HCMS).

We discovered that in the pre-sunrise hours, the impacts of vehicle emissions from a major freeway, including ultrafine particles (UFP), extended approximately a factor of ten further (~3000 m vs ~300 m) than during the day. UFP and NO concentrations were strongly correlated with traffic counts on the freeway during this period, but differences in mixing cause pollutant concentrations during pre-sunrise hours to be greater than during morning and afternoon hours, despite much higher traffic counts at those times. We associate the elevated pre-sunrise concentrations over a wide area with a nocturnal surface temperature inversion and low wind speeds, and believe this discovery has important exposure assessment implications.

MP measurements in Wilmington and Long Beach showed diesel truck-related pollutants such as black carbon, NO, and UFP were frequently elevated 2 to 6 times within 150 m downwind of freeways (compared to further away), and up to twice as high within 150 m of arterial roads with significant diesel truck traffic. Wind direction was a major determinant of impacts, but elevated pollution impacts downwind of freeways and arterials were roughly proportional to diesel volumes on the roadways and nearly constant for extended periods. Thus, persons living or working near and downwind of busy roadways can have several-fold higher exposures to diesel-related pollution than would be predicted by traditional fixed-site monitors, which are sited according to USEPA criteria intended to ensure measurements representative of air quality on a large neighborhood scale.

We measured real-time air pollutant concentrations downwind of the general aviation airport in Santa Monica. Elevated UFP concentrations were observed extending beyond 660 m downwind and 250 m perpendicular to the wind on the downwind side of the SMA takeoff area. Aircraft operations resulted in spikes of highly elevated pollutants, and mean UFP concentrations elevated by factors of 10 and 2.5 at 100 m and 660 m downwind, respectively, over background concentrations. BC levels were similarly elevated. Peak UFP concentrations were correlated (r2=0.62) with estimated fuel consumption rates for the departing aircraft. Our observations have potential health implications for persons living near general aviation airports.

In connection with the HCMS, we conducted the Harbor Communities Time Location Study (HCTLS) which integrated traditional recall diary activity logs with GPS tracking to document the patterns of 47 adult residents of port-adjacent communities, areas heavily impacted by heavy duty diesel trucks. We also conducted sampling of PM mass and number inside HCTLS participant residences during baseline and exit interviews, yielding the only indoor pollutant level data collected during the HCMS. The enhanced time-location database generated from logs, GPS and follow-up interview data significantly improved the amount (by a factor of 2) and quality of time-location data collected through recall diary activity logs alone. HCTLS participants were largely low-income, Hispanic women who on average spent about 89% of their day indoors and about 7% traveling. About one fifth of the participants resided within 200 m of a heavily-travelled roadway or truck route. On average, participants spent about 5 hours per day near roadways with high traffic volumes.