Understanding the creation, transport and transformation of particles and the contaminants they carry, is a critical focus of environmental engineering in both the agriculture and transportation sectors. This is an especially compelling area of research because of the recently documented links between adverse human health effects and exposure to airborne particulate matter. My interests have centered on contaminant transport processes in air and soil, with an emphasis on conducting field measurements. My research can be subdivided into three broad areas: 1) Environmental Particle Interface Chemistry; 2) On-road Vehicle Emissions; and 3) Nonpoint Source Particle Generation and Transport.

Environmental Particle Interface Chemistry

My experience with particle/surface geochemical processes initially started with my PhD thesis on the sorption kinetics of polycyclic aromatic hydrocarbons (PAHs) and expanded during my post-doctoral research to include polar organic compound interactions with mineral surfaces and microbially-assisted mineral dissolution kinetics. This work represents the fundamental basis for my current research on the environmental behavior of the more polar organic compounds, specifically pre-emergence herbicides applied to agricultural soils. Identification of the field conditions under which different herbicide classes are adsorbed to airborne soil particles and likely to be transported offsite has implications both for soil management practices and for land use planning in many areas of the U.S. where the agriculture/urban interface is increasingly important in terms of public health issues.
Just as herbicides may be transported by and transformed on particulate matter (PM), the surface chemical reactions taking place on vehicle-derived particles are of concern. Therefore, in addition to studying the gas/particle partitioning of agricultural chemicals to soil-derived PM2.5, the production of more toxic polar reaction products from vehicle PM in the atmosphere is also currently being studied in my group.

On-road Vehicle Emissions

Traditional studies of vehicle emissions have been laboratory-based and focused on quantifying the regulated gas emissions (hydrocarbons, oxides of nitrogen, carbon monoxide). My transportation research projects have departed from these traditions by focusing on particulate matter (PM) and making on-road, real-world measurements. A significant contribution in my first on-board measurement study identified differences in automobile gas exhaust emissions between individual drivers. In another transportation-air quality project, ultrafine and nanoparticles from vehicle exhaust were measured at roadside to characterize particle size distributions from in-use, on-road vehicles. Particulate matter studies have chiefly quantified total PM mass in response to emissions standards, but my recent research quantifies number-based ultrafine particle emissions, which are more relevant to adverse human health effects. I have also examined the particulate emissions from transit buses of different engine and after-treatment technologies. This work has led to new funding from local and regional transportation agencies to collect emissions data on-board transit buses and light-duty vehicles.

Nonpoint Source Particle Generation and Transport

Traditionally, emissions from stationary point sources such as power plants have been the focus of abatement efforts. However, with successes in the ability to further reduce emissions from stationary sources diminishing, the need to control emissions from nonpoint sources, which are more difficult to quantify and model, has grown. My research in this area has focused on quantifying particulate matter emissions from agricultural and quarry sources. PM emissions from agricultural operations are very difficult and costly to measure, but are essential for modeling air quality in many regions where a large proportion of land is devoted to agriculture. My studies of PM from agriculture and quarry operations have involved innovative measurement techniques. For example, the quantification of crystalline silica, a suspected carcinogen, in airborne dust samples downwind of nonpoint sources was investigated using a novel application of aerosol analysis techniques (Proton Induced X-ray Emission, PIXE) coupled with X-ray diffraction. In a series of papers, the application of the miniature elastic LIDAR (LIght Detection And Ranging) instrument to revolutionize measurement for PM10 emissions from nonpoint agricultural sources has been described. Our lidar publications are the first to combine lidar with traditional point sampling methods for measuring PM10 fluxes. Further, we have used lidar data to determine how field-scale measurements should be scaled up for regional air quality models and highlight the importance of incorporating variability into emission factor calculations, a practice that is too often ignored. Several conference papers have also examined using lidar to make range-resolved wind speed and direction measurements. This particle emissions work is continuing under a new USDA grant where we are quantifying agricultural PM2.5 emissions in Connecticut and New Mexico with real-time point samplers and lidar.