Highly resolved spatiotemporal variability of fine particle number concentrations in an urban neighborhood

Abstract

Many research efforts are dedicated to study the high spatiotemporal variability of fine and ultrafine particle concentrations in the urban environment, due to reported associations between exposure to fine particles and plethora of health outcomes. To study the inner-neighborhood variability of such particles, we measured the number concentration of fine particles for six months in five locations across an urban residential neighborhood, using a network of compact optical particles counters. This setup enabled us to apply a wavelet analysis to study the variability of the particle number concentration at different time-scales. Analysis of the particle number concentration (PNC) time series revealed common patterns that could be attributed to regional background PNC, and to neighborhood-scale processes with typical time-scales >4h. Spatially heterogeneous (i.e. local) features in the observed PNC, evident at smaller scales with typical time scales <4h, had no clear long-time pattern. The variability across the neighborhood materialized mainly in the upper percentiles of the PNC distribution rather than in its central measures, revealing a prominent right tail (skewness >1). Wavelet resolved temporal scales of the PNC and wind measurements showed similar spatial patterns, with the correlation between the wavelet coefficients of the two signals mirroring typical temporal and spatial dispersion characteristics at the corresponding scales.