Locating nearby sources of air pollution by nonparametric regression of atmospheric concentrations on wind direction

The relationship of the concentration of air pollutants to wind direction has been determined by nonparametric regression using a Gaussian kernel. The results are smooth curves with error bars that allow for the accurate determination of the wind direction where the concentration peaks, and thus, the location of nearby sources. Equations for this method and associated confidence intervals are given. A nonsubjective method is given to estimate the only adjustable parameter. A test of the method was carried out using cyclohexane data from 1997 at two sites near a heavy industrial region in Houston, Texas, USA. According to published emissions inventories, 70% of the cyclohexane emissions are from one source. Nonparametric regression correctly identified the direction of this source from each site. The location of the source determined by triangulation of these directions was <500 m from that given in the inventory. Nonparametric regression is a powerful technique that has many potential uses in air quality studies and atmospheric sciences.