Chemical and Physical Characterization of Non-Tailpipe and Tailpipe Emissions at 100 Locations near Major Roads in the Greater Boston Area
Petros Koutrakis, Brent Coull, Marco Martins, Joy Lawrence, and Stephen Ferguson
Harvard TH Chen School of Public Health, Boston MA, USA
Background: The purpose of the proposed research is to develop sampling and statistical analysis methods to improve assessment of exposure to traffic particles and pollutants for health effects studies, characterize direct (tailpipe and non-tailpipe) and indirect contributions, and identify parameters which influence them.
Methods: Using a mobile sampling platform equipped with coarse and fine particulate matter (PM) concentrators we are collecting ambient ultrafine, fine minus ultrafine (accumulation mode), and coarse particle samples near roads in the Greater Boston. In addition, we are collecting PM2.5 and PM10 samples of aerosolized surface road dust in situ, using a Road Dust Aerosolization sampler. We are collecting these road dust and ambient PM samples at three distance ranges (including background) from each of the 100 major (A1, A2, and busy A3) road sites included in this study. The sampling time for ambient particles for each position is one hour, and the road dust sampling duration is 5 min. Each day of sampling, we also collect continuous particle count, particle mass, traffic, and weather data at all 3 locations simultaneously, to assess temporal variability at sites. Potential sites are identified using Google Earth/Google Maps and then evaluated during a site visit. To address temporal variability, a subset of sites will be visited multiple times in different seasons.
Results: Following completion of the mobile platform assembly with fine and coarse concentrators, we did several days of performance validation. We found an excellent agreement between concentration and composition of duplicate samples collected using both the fine and coarse particle concentrators. During validation, an average enrichment factor of 10.9 times was observed for the fine particle concentrator and 80.2 times for the coarse particle concentrator.
We started the field measurements, and have completed a small number of sites. As the measurements have recently begun and are ongoing, our data are limited. However, we observed an average enrichment factor for fine concentrated particles in Framingham was 8.8 times ambient and 9.8 times for Marlborough. So far, enrichments have been highest at the Road site as compared to background or intermediate sites. All filters had enough loading for XRF and EC/OC analysis.
For the road dust samples, Framingham showed higher loading on filters for both PM2.5 and PM10, compared to Marlborough. All Road Dust filters also had enough collected material in 5 min sampling to perform XRF analysis.
Conclusions. The validation testing and preliminary results from our two sites show that the mobile platform is functioning as intended, resulting in short duration ambient samples which can be analyzed for trace elemental composition, elemental carbon, and organic carbon.