Urban-scale variability of ambient particulate matter attributes

Real-time sampling of ambient particulate matter (PM) in the size range 0.23–10 μm and of carbonaceous matter concentrations has been carried out in a carefully designed field campaign in proximate paired neighborhoods in Haifa, Israel. The paired sites are characterized by a similar population density and neighborhood-wise socioeconomic (deprivation) index but show distinct canopy coverage. The data indicate clear sub-urban (neighborhood) scale variations in any measured PM attribute, such as concentrations, size distribution, and carbonaceous matter content. Mean ambient PM levels were comparatively higher than in other urban studies whereas carbonaceous airborne PM concentrations were lower. On top of the diurnal and seasonal variability and in spite of the significant regional effect of the semi-arid climate, local emissions and removal processes affect the PM concentrations to which people residing in urbanized regions are exposed. Analysis of possible mechanisms that could affect the observed spatial sub-urban PM differences, including local meteorology and emissions, reveal that sub-urban variability of removal processes has a major influence on ambient PM levels. Observations suggest that on top of the regional air masses which affect the city air quality and emissions from local sources, a normally unnoticed removal process, showing urban scale variability, is interception by trees and dense vegetation. In particular, the observed sub-urban variability in ambient PM concentrations is attributed, in part, to local variation of removal processes, among them the neighborhood-wise deposition on available surfaces, including canopy.