Averaging the concentrations across all sites indicated
~70% of the PM10 were fine particles (PM2.5). However,
there is a considerable variability in daytime and nighttime
ratios, in addition to the variation between individual
measurements. The ratio of fine mass to coarse mass in
outdoor air in the H area was slightly higher than that in
the L area (see Table 3), and the correlation coefficient of
PM2.5 and PM2.5-10 was higher in the H area than in the L
area. This reflected that the fine particles in the H area of
Bangkok are from automobiles rather than from soil dust.
The correlation between fine and coarse particles is greater
in the H area than in the M and L areas. The study of the
contribution of PM2.5 to PM10 should be developed further,
and more parallel measurements could help to estimate
PM2.5 levels from the existing PM10 data. The study
of police exposure to PM10 indicated good agreement between
personal monitoring data and ambient level at the
intersections. However, the personal exposure level of
PM2.5 was higher than the atmospheric level. Likewise,
there was a good correlation between the PM concentration
measured by the sampler and data from the PCD;
however, the absolute level between the two measurements
showed a significant difference.
Because the monitoring data were not available at
exactly the same time as our personal measurement for
PM exposure, the ambient particulate level at the roadside
could not be compared directly with personal exposure.
Further investigation on the differences between
monitoring sites and the atmospheric environment at
the intersections should be considered, such as the distance
from monitoring stations to the emission areas,
other possible particulate sources, and related meteorological
conditions. It is also important, because of the
large variation of the level of air pollutants throughout