**4. Conclusion**

42 Atmospheric Aerosols – Regional Characteristics – Chemistry and Physics

Morning (Rama6, Apr 2006)

ultrafine accumulation coarse

μg/g

Phe

Ant

Fluo

Pyr

BaA

Chr

BbF

BkF

BeP

BaP

IP

μg/g

Phe

Ant

Fluo

ultrafine accumulation coarse

Pyr

BaA

Overnight (Rama6, Apr 2006)

Chr

BbF

BkF

BeP

BaP

IP

DahA

BghiP

μg/g

Phe

Ant

Fluo

ultrafine accumulation coarse

Pyr

Evening (Rama6, Apr 2006)

BaA

Chr

BbF

BkF

BeP

BaP

IP

DahA

BghiP

μg/g

Phe

Ant

Fluo

ultrafine accumulation coarse

Pyr

Daytime (Rama6, Apr 2006)

BaA

Chr

BbF

BkF

BeP

BaP

IP

DahA

BghiP

μg/g

Phe

Ant

Fluo

Pyr

BaA

Chr

BbF

BkF

BeP

BaP

IP

DahA

BghiP

μg/g

Phe

Ant

Fluo

Pyr

BaA

Overnight (CC, Apr 2006)

whole size range

Chr

BbF

BkF

BeP

BaP

IP

DahA

BghiP

μg/g

Phe

Ant

Fluo

Pyr

Evening (CC, Apr 2006)

whole size range

BaA

Chr

BbF

BkF

BeP

BaP

IP

DahA

BghiP

μg/g

Phe

Ant

Fluo

ultrafine accumulation coarse

Pyr

Daytime (CC, Apr 2006)

BaA

Chr

BbF

BkF

BeP

BaP

IP

DahA

BghiP

Morning (CC, Apr 2006)

ultrafine accumulation coarse

N.B.) The particulate weight data of the ultrafine mode for CC evening, and size distribution data of particle weight for

**Figure 10.** 13 PAH contents in the three particle modes in the four time periods of day (ultrafine: <

CC overnight were not obtained, thus their mode distribution data are not available in the figure.

DahA

BghiP

0.18μm, accumulation: 0.18-1.8μm, coarse: 1.8μm <)

This study clearly showed diurnal variations of particle size distribution of PAHs in four different time periods of day by field measurements on the two different types of roads in Bangkok, Thailand. The data indicated possible influences on the temporal variations of size distribution of PAHs by diurnal changes in traffic emissions, road configurations in relation to dispersion efficiency, meteorological conditions, atmospheric processes of particles such as coagulation, condensation and photochemical reactions under daytime sunlight, also atmospheric processes of PAHs in the accumulation particle mode. In view of people's exposure to vehicular emissions in an urban area with heavy road traffic, it is desired that urban air quality monitoring should be conducted in more comprehensive ways with higher resolutions of time and space, and actual behavior of pollutants be elucidated by various advanced approaches.
