Size-specific Particulate Matter Research Articles

Inferring deposition velocities from changes in aerosol size distributions downwind of a roadway

Abstract Deposition velocities for particulate matter (PM) from road traffic in the Lake Tahoe basin were estimated with a mass-balance model and measurements using four size-specific PM profilers and meteorological instruments located at 15 m upwind and 5, 30 and 100 m downwind of major highway in the Lake Tahoe basin. Coarse PM (2.5–10 μm) concentration decreased exponentially with downwind distance from the highway. With tall aspen trees barrier, at 30 m and 100 m downwind, the PM10 mass concentrations decreased respectively to 51% and 11% from the observed concentrations at 5 m. Particles with diameters between 0.3 and 0.5 μm show almost a homogeneous distribution across the road indicating the smallest particles are unrelated to a road source. Calculated deposition velocities generally increased with particle size and ranged from 15 μm diameter, which is consistent with the Stokes settling velocities, implying the Stokes settling velocities may represent a reliable lower bound on the deposition rate. The wind speed and direction play important roles in determining the deposition velocities of road traffic induced particles. Higher PM concentrations were observed when strong onshore winds dominated during the daytime coupled with high traffic counts. Between late afternoon and early morning, offshore winds blew traffic induced PM towards the Lake, where they could deposit and impact the water clarity.

Circulating neutrophil CD14 expression and the inverse association of ambient particulate matter on lung function in asthmatic children

Identifying baseline inflammatory biomarkers that predict susceptibility to size-specific particulate matter (PM) independent of gaseous pollutants could help us better identify asthmatic subpopulations at increased risk for the adverse health effects of PM. To evaluate whether the association between lung function and exposure to ambient levels of PM less than 2.5 microm in diameter (PM2.5) (fine) and 10 to 2.5 microm in diameter (PM(10-2.5)) (coarse) in children with persistent asthma differed across baseline measures of inflammation and innate immune activation. We performed a panel study on a local population of 16 children with persistent asthma and evaluated daily pulmonary function (percentage of predicted peak expiratory flow and forced expiratory volume in 1 second) while concurrently measuring daily PM2.5 and PM(10-2.5) exposure from a central site in Chapel Hill, North Carolina. The children underwent a baseline medical evaluation that included assessment of several immunoinflammatory biomarkers in peripheral blood. Children without measurable CD14 expression on circulating neutrophils had significantly reduced pulmonary function (forced expiratory volume in 1 second and peak expiratory flow) with each interquartile range (IQR) increase in PM2.5 (IQR = 8.5 microg/m3) and PM(10-2.5) (IQR = 4.1 microg/m3) concentration, unlike children with measurable CD14 expression (P < .001 for interaction). Asthmatic children with muted surface expression of CD14 on circulating neutrophils may have a decreased capacity to respond to bacterial components of PM.

Graphical Analysis of the Performance of Venturi Scrubbers for Particle Abatement. Part II: Size Distribution of Penetrating Particles

Graphical tools are developed that provide convenient estimation of the size distribution of particles penetrating venturi scrubbers, based on the well-established theoretical formulations of Calvert (1970) and Yung et al. (1978). The graphical solutions, produced through functional analysis and numerical methods, deliver the accuracy of the original theoretical models under the specified venturi design and operating conditions, subject to the assumption of lognormal input particle size distribution. While Part I describes estimation of the overall particle abatement efficiency, the work in this article allows estimation of the size distribution of emitted particles. The generated nomographs can therefore be used as part of a methodology for compiling size-specific particulate matter emission inventories.