ISSN 2630-0583 (Print)
ISSN 2630-0656 (Online)
Journal of Current Science and Technology
Rangsit Journal of Arts and Sciences. Vol.3 No.1 , January - June 2013.
Carbon composition of PM10 and PM2.5 in Bangkok ambient air from a city center sampling site
PM10 and PM2.5 concentrations can adversely affect the respiratory and cardiac health of humans and also reduce visibility. Black carbon (BC) aerosols absorb solar radiation and have been shown to be the second largest contributor to global warming after greenhouse gases. Organic carbon (OC) and elemental carbon (EC) composition differs for different emission sources, and this difference is useful in identifying and controlling both PM2.5 and BC, the two major causes of air pollution and global warming. The objectives of this study were to measure the carbon composition of aerosols and to find relationships among the different constituents that can be used to identify the emission sources of PM10, PM2.5 and BC in the ambient air of the Bangkok city center at Chulalongkorn University. PM10 and PM2.5 were collected with a dichotomous air sampler located on the roof of the five-story Environmental Engineering building. The samples were collected for 24 hours every 6 days in both dry and wet seasons from December, 2011, to July, 2012. OC and EC were analyzed with thermal-optical methods. Concentrations of BC were measured with a microaethalometer for 15 days in the dry season. The results showed that in the dry season, the average PM10 and PM2.5 concentrations were 80 µg/m3 and 48 µg/m3, respectively. The average ratio of PM2.5 to PM10 concentrations was 0.60. In the wet season, PM10 and PM2.5 concentrations were less than in the dry season: 45 µg/m3 and 23 µg/m3, respectively. The average ratio of PM2.5 to PM10 concentrations was 0.51. The PM10 and PM2.5 concentrations in the wet season were approximately half of the concentrations in the dry season. BC concentrations ranged from 2.33 – 5.50 µg/m3, with a mean of 3.64 µg/m3. A diurnal variation was observed, with the highest values occurring on weekdays at approximately 6–9 a.m. and in the evening, which correspond to peak traffic in the morning and afternoon. In the dry season, the average concentration of EC in the PM2.5 was 3.04 µg/m3. The ratio of total carbon (TC), OC and EC concentrations to the PM2.5 concentration were 0.35, 0.29 and 0.06, respectively. The average ratio of OC to EC concentration in PM2.5 was 4.52. The average ratio of the Char-EC to Soot-EC concentration in PM2.5 was 1.70. Major fractions of eight carbon fractions (OC1, OC2, OC3, OC4, EC1, EC2, EC3 and optically detected pyrolyzed carbon (OP)) were EC1- and OP-enriched in motor vehicle exhaust. We conclude that controlling motor vehicle emissions is the most important factor in controlling both particulate matter and black carbon in the Bangkok city center ambient air.