Concentration and Size Distribution of Ultrafine Particles Near a Major Highway

Abstract

Motor vehicle emissions usually constitute the most significant source of ultrafine particles (diameter <0.1 µm) in an urban environment, yet little is known about the concentration and size distribution of ultrafine particles in the vicinity of major highways. In the present study, particle number concentration and size distribution in the size range from 6 to 220 nm were measured by a condensation particle counter (CPC) and a scanning mobility particle sizer (SMPS), respectively. Measurements were taken 30, 60, 90, 150, and 300 m downwind, and 300 m upwind, from Interstate 405 at the Los Angeles National Cemetery. At each sampling location, concentrations of CO, black carbon (BC), and particle mass were also measured by a Dasibi CO monitor, an aethalometer, and a DataRam, respectively. The range of average concentration of CO, BC, total particle number, and mass concentration at 30 m was 1.7-2.2 ppm, 3.4-10.0 µg/m 3 , 1.3-2.0 × 10 5 /cm 3 , and 30.2-64.6 µg/m 3 , respectively. For the conditions of these measurements, relative concentrations of CO, BC, and particle number tracked each other well as distance from the freeway increased.Particle number concentration (6-220 nm) decreased exponentially with downwind distance from the freeway. Data showed that both atmospheric dispersion and coagulation contributed to the rapid decrease in particle number concentration and change in particle size distribution with increasing distance from the freeway. Average traffic flow during the sampling periods was 13,900 vehicles/hr. Ninetythree percent of vehicles were gasoline-powered cars or light trucks. The measured number concentration tracked traffic flow well. Thirty meters downwind from the freeway, three distinct ultrafine modes were observed with geometric mean diameters of 13, 27, and 65 nm. The smallest mode, with a peak concentration of 1.6 × 10 5 /cm 3

Characterizing the range of children's air pollutant exposure during school bus commutes

“…Comparison to Near-roadway and Ambient Concentrations Zhu et al (2002b) measured roadside concentrations of BC along the I-405 in LA, the same freeway traveled during bus commutes on U1 in our study, and found a mean concentration of 5.4 mg/m 3 next to the freeway, which reduced to 1.3 mg/m 3 at a site 300 m downwind of the freeway. The 300 m downwind concentration is comparable to the mean ambient BC concentrations we measured near either end of U1 of 1.3-2.9 mg/m 3 .…”

Repeated hospital encounters for asthma in children and exposure to traffic-related air pollution near the home

“…6 We did not include background pollutant concentrations because variability is likely low within the 13-km study radius. Dispersion-modeled gases are considered surrogates of other more toxic gases and particles emitted from nearby diesel trucks and automobiles, including ultrafine particles that have been found at notably higher concentrations near roadways along with black carbon, particle number, and CO. 29 The stronger associations for NO x compared with NO 2 support this because NO 2 is strongly affected by photochemical reactions that can occur across time away from roadways, whereas NO x is expected to capture traffic emissions more generally. 30 Key pollutants likely represented by NO x and CO are those carried by ultrafine particles.…”

Personal exposure to ultrafine particles

“…Outdoor UFP concentrations were measured for 1-2 years in several US cities (U.S. EPA Supersites program; Solomon et al, 2008), and near roadways in California (Zhu et al, 2002) and also in Erfurt and Augsberg, Germany (Wichmann et al, 2000). Residential indoor concentrations have also been reported (Abt et al, 2000;Dennekamp et al, 2001;Long et al, 2001;Wallace and Howard-Reed, 2002;Klepeis et al, 2003;He et al, 2004;Wallace, 2000Wallace, , 2005Wallace, , 2006Wallace et al, 2004Wallace et al, , 2008Hoek et al, 2008).…”