Spatial Variation of Particle Number Concentration in School Microscale Environments and Its Impact on Exposure Assessment
Salimi, F and Mazaheri, M and Clifford, S and Crilley, LR and Laiman, R and Morawska, L, Spatial Variation of Particle Number Concentration in School Microscale Environments and Its Impact on Exposure Assessment, Environmental Science & Technology, 47, (10) pp. 5251-5258. ISSN 0013-936X (2013) [Refereed Article]
It has not yet been established whether the
spatial variation of particle number concentration (PNC)
within a microscale environment can have an effect on
exposure estimation results. In general, the degree of spatial
variation within microscale environments remains unclear,
since previous studies have only focused on spatial variation
within macroscale environments. The aims of this study were
to determine the spatial variation of PNC within microscale
school environments, in order to assess the importance of the
number of monitoring sites on exposure estimation.
Furthermore, this paper aims to identify which parameters
have the largest influence on spatial variation as well as the
relationship between those parameters and spatial variation.
Air quality measurements were conducted for two consecutive weeks at each of the 25 schools across Brisbane, Australia. PNC
was measured at three sites within the grounds of each school, along with the measurement of meteorological and several other
air quality parameters. Traffic density was recorded for the busiest road adjacent to the school. Spatial variation at each school
was quantified using coefficient of variation (CV). The portion of CV associated with instrument uncertainty was found to be 0.3,
and, therefore, CV was corrected so that only noninstrument uncertainty was analyzed in the data. The median corrected CV
(CVc) ranged from 0 to 0.35 across the schools, with 12 schools found to exhibit spatial variation. The study determined the
number of required monitoring sites at schools with spatial variability and tested the deviation in exposure estimation arising
from using only a single site. Nine schools required two measurement sites and three schools required three sites. Overall, the
deviation in exposure estimation from using only one monitoring site was as much as 1 order of magnitude. The study also tested
the association of spatial variation with wind speed/direction and traffic density, using partial correlation coefficients to identify
sources of variation and nonparametric function estimation to quantify the level of variability. Traffic density and road to school
wind direction were found to have a positive effect on CVc and, therefore, also on spatial variation. Wind speed was found to have
a decreasing effect on spatial variation when it exceeded a threshold of 1.5 (m/s), while it had no effect below this threshold.
Traffic density had a positive effect on spatial variation and its effect increased until it reached a density of 70 vehicles per five
minutes, at which point its effect plateaued and did not increase further as a result of increasing traffic density.
particle number concentration, spatial variation, microscale