| Abstract | Polycyclic aromatic hydrocarbons (PAHs) were of concern due to their toxic and carcinogenic effects. PAHs are the product of incomplete combustion and the most significant source of airborne PAHs is the anthropogenic activities such transportation, biomass burning, domestic cooking, and waste burning. In Thailand, the information on associated sources and a systematic database of PAHs are still limited, and the monitoring of PAHs has not been well established as compared to the criteria air pollutants. In this study, 24h samples of PAHs were collected separately for particulate (PM) and gas (G) phases using a Hivol-PUF sampler. The sampler was placed on the roof top of the Energy building in the AIT campus, Thailand. The samples were collected during wet (September –October, 2017) and dry season (November 2017 –January 2018) yielding a total of 28 samples. These samples (28 filters and 28 PUF) were extracted by ultrasonication and analyzed for 16 US EPA priority PAHs by GC-MS. The average PM-PAHs (15compounds) concentration at the site during the wet and dry season were 1.08 ± 0.51 ng/m³ and 4.60 ± 2.17 ng/m³, respectively. While the G-phase average concentrations in wet and dry season were 15.14 ± 11.43 ng/m³ and 26.01 ± 15.82 ng/m³, respectively. G-PAHs had the predominant share with over 83% of the total PAHs in the wet season and 70% in the dry season. Low molecular weight PAHs (3 rings, including Acy, Ace, Flo, Phe, and Ant) were the dominant in both wet and dry season, i.e consisting of about 49% and 52% of the total 16 PAHs in both phase, respectively. Medium molecular weight (4-rings) PAHs collectively accounted for 30 and 33% of the total PAHs in wet and dry season, respectively. The high molecular weight PAHs (5-6 rings) accounted for only 21% in wet season and 15% in dry season. The diagnostic ratios of PAHs were calculated to identify the main contributing sources. The quantitative contribution of emission sources to the measured PAHs levels at the site was determined using the Chemical Mass Balance (CMB) receptor model. The results showed that the major contributor to the total PAHs in wet season was four-stroke motorcycle (33%), gasoline engine (27%), and wood combustion (16%). In the dry season, gasoline engine was the highest contributor (20%) followed by charcoal combustion (19%), and biomass burning (14.6%). The major contribution sources of PM-PAHs in wet and dry season were four stroke-motorcycle (47%) and wood combustion (41%). For G-PAHs, wood combustion had the highest contribution in wet season (36%) and dry season (40%). The pollution rose results showed the consistent results of the locations of major local contributing sources identified by CMB. The northeast and southeast directions to the site coincided with the main road location hence confirming the influence of the traffic sources (four stroke motorcycle and gasoline engine). The residential area was affected from the north and northeast of the site which was the direction of the residential combustions (included charcoal and wood as fuel). The biomass open burning in the study area would be mainly the rice straw filed burning which had the high contribution from the north. Agricultural field was also located around the campus particularly in the north direction. The results of HYSPLIT back trajectories showed that the high levels of long-lived PAHs (B[a]A, D[ah]A, Pyr, B[a]P, B[b]F, B[k]F) were associated with the air mass trajectories having pathways originated from northeast over the continental territories with regional stagnant conditions. The lower levels of long-lived PAHs were associated with the air mass trajectories originated mainly from the ocean with a long marine pathway. PAHs monitoring results and the possible sources identified in this study contribute to the air quality database of this toxic pollutant group. The preliminary source apportionment results should be further improved with more monitoring data and advanced receptor models. The refined source apportionment results will be useful information for policy making to reduce the levels of these toxic pollutants in BMR. |