Mobile Monitoring of Particulate Black Carbon Concentrations in an Urban Area

Abstract

P-653 Introduction: Interest in chronic exposure to air pollution has led to an increased focus on the spatial distribution of traffic related air pollutants within urban environments. Measuring this distribution has usually involved using numerous fixed-site passive NO2/NOx badges simultaneously deployed for a week or more. Here we describe a relatively simple mobile monitoring method for particulate black carbon intended to complement the fixed-site NOx sampler approach. Methods: A particle soot absorption photometer (psap) and accompanying pump were placed inside a conventional gasoline powered vehicle and powered with a marine battery connected through an inverter. The instrument sampled air from the driver side rear window and the readings were recorded each second with a serial datalogger. The vehicle was driven continuously along one of six routes. These routes were driven during peak afternoon traffic periods (∼4 to 7 PM) between July and August, 2005 and were chosen to include 36 roadway intersections previously sampled for NO2 and NOx using a simultaneous, fixed-site sampler array. Initial attempts at sampling during morning rush hour resulted in less stable measurements due to rapid temporal variability in the mixing height. One centrally located intersection was visited during each afternoon mobile sampling period. From 5 to 8 additional locations could also be sampled during any given sampling period. The vehicle traced a cloverleaf pattern at each intersection, circling the four adjacent blocks surrounding the intersection and thus passing through the actual intersection four times. The average psap readings taken during this cloverleaf traverse were used in subsequent analyses. The ratio of the average reading at each site to that at the central site was computed for each run and then averaged across all sample periods. These average site ratios were then compared with the 5 day average NOx concentraions measured previously at 36 separate locations. Results: We found a high correlation between the mobile Black Carbon and fixed site NOx measurements (r = 0.77). Discussion and Conclusions: We were able to identify the relative impact of traffic emissions at numerous locations using a simple mobile sampling strategy. The strong correlation between this method and the passive sampling network data is encouraging, given that we only sampled at any given intersection for about 10 minutes, that we were measuring black carbon rather than NOx, and that NOx and black carbon measurements were not made simultaneously nor adjusted for seasonal variability.