Characterization and nonparametric regression of rural and urban coarse particulate matter mass concentrations in northeastern Colorado

The Colorado Coarse Rural Urban Sources and Health study (CCRUSH) is an ongoing study of the relationship between coarse particulate mass concentrations (PM₁₀₋₂.₅, particulate matter with diameter between 2.5 and 10 μm) and selected health effects. For two urban monitoring sites in Denver, CO, and two comparatively rural sites in Greeley, CO, hourly mass concentrations of PM₁₀₋₂.₅ and fine particulate matter (PM₂.₅, diameter less than 2.5 μm) have been measured by using dichotomous tapered element oscillating microbalances (TEOMs) with Filter Dynamics Measurement Systems (FDMS). This paper presents air quality results from just over a year of PM₂.₅ and PM₁₀₋₂.₅ measurements. Average PM₂.₅ concentrations ranged from 7.7 to 9.2 μg m⁻³ across the four sites with higher concentrations in Denver than Greeley. Average PM₁₀₋₂.₅ concentrations ranged from 9.0 to 15.5 μg m⁻³ with the highest values at the site in northeast Denver. Temporal variability in PM₁₀₋₂.₅ was higher than that in PM₂.₅ concentrations at all four sites. The two Greeley sites displayed moderate spatial correlation for PM₂.₅ and high correlation for PM₁₀₋₂.₅, whereas the two Denver sites showed lower spatial correlation for both PM sizes. PM₁₀₋₂.₅ concentrations in Denver were highest with winds from the direction of the city's urban core. PM₁₀₋₂.₅ concentrations in Greeley were moderately elevated with winds from the southwest to the northwest, coming from Denver and other large Front Range communities. Wind speed regressions for PM₁₀₋₂.₅ at the Denver sites primarily exhibited resuspension effects, while PM₁₀₋₂.₅ concentrations in Greeley showed relatively complex wind speed dependence.