PM2.5 and PM10 cascade, placed in the center of the
Dindaeng intersection, with that on the top of the
Dindaeng PCD monitoring station, which was located at
the roadside 300 m from the intersection. PM10 and PM2.5
datawere closely correlated at the two simultaneous measurement
sites. Correlation coefficients were 0.80 for PM2.5
and 0.88 for PM10. The slope of the regression line was
0.50 with an intercept of 113 µg/m3, suggesting higher
PM levels at the intersection site.
Figure 4 shows the correlation between PM2.5 and
PM10 measured outside the booth and personal exposure.
There was a good correlation between personal exposure
and the ambient air outside the police booth for both
PM2.5 and PM10. There was a better association than the
correlation in Figure 3 because the sampling sites were
in the same areas as the personal exposure measurements.
The correlation coefficients of both PM2.5 and PM10 increased
to 0.92.
PM Level in Bangkok
The data of eight PCD monitoring stations in the metropolitan
area were accessed from the Web site http://
www.pcd.go.th/AirQuality/bangkok/. The high-volume air
sampling method was specified in the Thai Air Quality
Standard for PM10, but in the case of online data, it was
conducted by β-ray attenuation, which was standardized
against the conventional method. In this study, data from
eight monitoring stations (Table 3) were used for site selection.
These continuous data also reflected the trend of
PM levels.2 Among them, Dindaeng and Ramkhamhaeng
were selected as sampling sites. As can be seen in Table 4,
PCD data of the annual arithmetic average PM10 concentration
at the Dindaeng roadside monitoring station for
the last 3 years varied between 73 and 130 µg/m3
, whereas
for the general area at Ramkhamhaeng, the data varied
between 53 and 62 µg/m3
. In 1997, the annual average
PM10 exceeded 100 µg/m3 at the two roadside stations but
decreased to 80 µg/m3 in 1999. The decreasing tendency
also was observed in the general area monitoring stations.
The proportion of days when the level of 24-hr average
PM10 exceeded the NAAQS of 120 µg/m3 in 1997–2000 were
reduced annually, as shown in Table 3. In the three roadside
stations, the average percentage of the days on which
the PM10 level was found to be higher than the NAAQS
decreased from 27 to 11%, and in the five general area
monitoring stations, the equivalent data decreased from
9 to 3%. The relationship between PM10 and NO2
or SO2
for the last 3 years, both in the roadside and general area
stations, is illustrated in Table 4. While the correlation
coefficients between PM10 and SO2 were small, PM10 and
NO2 were high at all eight stations.