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Several empirical studies of reductions in air pollutants as social distancing and working from home (WFH) policies have sparked recommendations that the COVID-19 pandemic might have been responsible for better air quality particularly in urban area. These findings offer a compelling provocation for the scientific community to detect and investigate variations to air quality as a consequence of government enforced quarantine. In spite of countless research studies focusing on the connection between WFH policy and air pollutant levels, the majority of discussion has unfortunately ignored the central role of other potential sources (e.g. agricultural waste burnings, cooking emissions, and industrial releases) in governing air quality, or has neglected the psychological and social impacts of COVID-19. In this study, a t test was used to compare the average concentrations of PM2.5 and COVID-19-infected numbers (n) in three different periods which were n

Levoglucosan, as a biomass tracer, and sixteen polycyclic aromatic hydrocarbons (PAHs) in PM2.5 ambient air samples collected from Tak Province during smoke and non-smoke episodes were analyzed. The average PM2.5, levoglucosan and total PAHs concentrations in the smoke episode were 61.64 ± 22.85, 1.00 ± 0.41 μg/m3 and 6.32 ± 2.26 ng/m3, respectively. This figures were significantly higher than those recorded during the non-episode (13.76 ± 5.58, 0.12 ± 0.03 μg/m3 and 2.59 ± 0.15 ng/m3, respectively). The predominant PAHs proportions were comprised of Phenanthrene and Benzo[ghi]perylene and levoglucosan concentrations revealed a strong correlation with PM2.5 concentrations, which indicated the source of PM2.5 from biomass burning. Toxicity equivalent (TEQBaP) and the mutagenic equivalent (MEQBaP) levels during the smoke episode were significantly higher than those in the non-smoke episode. Furthermore, lifetime lung cancer risk recorded during smoke episode exceeded the acceptable cancer risk that has been recommended by US-EPA. These results suggest that this area was not only exposed to PAHs that originated from traffic combustion, but was also exposed from biomass burning emissions, particularly during biomass burning season when there is an increased risks of cancer and mutation. Although the exposure time in this area is relatively short, the high dose period of exposure occurs repetitively every year. In addition, backward trajectories showed that most of the air mass was generated from western region of Thailand and they were throughout the burning region not only emitted from local areas, but also from outside the country during the smoke episode.

Size-segregated ambient particles down to particles smaller than 0.1 μm (PM0.1) were collected during the year 2014–2015 using cascade air samplers with a PM0.1 stage, at two cities in Thailand, Bangkok and Chiang Mai. Their characteristics and seasonal behavior were evaluated based on the thermal/optical reflectance (IMPROVE_TOR) method. Diagnostic indices for their emission sources and the black carbon (BC) concentration were assessed using an aethalometer and related to the monthly emission inventory (EI) of particle-bound BC and organic carbon (OC) in order to investigate the contribution of agricultural activities and forest fires as well as agro-industries in Thailand. Monthly provincial EIs were evaluated based on the number of agricultural crops produced corresponding to field residue burning and the use of residues as fuel in agro-industries, and also on the number of hot spots from satellite images corresponding to the areas burned by forest fires. The ratio of char-EC/soot-EC describing the relative influence of biomass combustion to diesel emission was found to be in agreement with the EI of BC from biomass burning in the size range

A personal inhalation exposure and cancer risk assessment of rural residents in Lampang, Thailand, was conducted for the first time. This highlighted important factors that may be associated with the highest areal incidence of lung cancer. Personal exposure of rural residents to polycyclic aromatic hydrocarbons (PAHs) and their nitro-derivatives (NPAHs) through inhalation of fine particulate matter (PM2.5) was investigated in addition to stationary air sampling in an urban area. The personal exposure of the subjects to PM2.5 ranged from 44.4 to 316 μg/m3, and the concentrations of PAHs (4.2–224 ng/m3) and NPAHs (120–1449 pg/m3) were higher than those at the urban site, indicating that personal exposure was affected by microenvironments through individual activities. The smoking behaviors of the rural residents barely affected their exposure to PAHs and NPAHs compared to other sources. The most important factor concerning the exposure of rural populations to PAHs was cooking activity, especially the use of charcoal open fires. The emission sources for rural residents and urban air were evaluated using diagnostic ratios, 1-nitropyrene/pyrene, and benzo[a]pyrene/benzo[ghi]perylene. Their analyses showed a significant contribution to emission from residents’ personal activities in addition to the atmospheric environment. Furthermore, the personal inhalation cancer risks for all rural subjects exceeded the USEPA guideline value, suggesting that the residents have a potentially increased cancer risk. The use of open fires showed the highest cancer risk. A reduction in exposure to air pollutants for the residents could potentially be achieved by using clean fuel such as liquid petroleum gas or electricity for daily cooking.

Chiang Mai and several other provinces in northern Thailand have been annually facing air pollution problems during the dry season. Ten polycyclic aromatic hydrocarbons (PAHs); 19 nitropolycyclic aromatic hydrocarbons (NPAHs); and levoglucosan (LG), a marker for biomass burning, were quantified in total suspended particulates (TSP) collected in Chiang Mai during the dry, transition, and wet seasons in 2010. The concentrations of PAHs and NPAHs in the dry season were significantly higher than in the wet season. The [Benzo[a]pyrene (BaP)] – [benzo[ghi]perylene (BghiPe)] ratio, as an indicator of traffic, and the correlations of PAHs and NPAHs with LG showed that biomass burning significantly contributes to air pollution in the dry season. 9-Nitroanthracene (9-NA) was the most abundant NPAH which suggests that 9-NA is generated from biomass burning. We proposed the [9-NA] – [1-nitropyrene (1-NP)] ratio as a new indicator for assessing the contribution of biomass burning. Biomass burning was a major source of PAHs and NPAHs in the dry season, whereas vehicle exhaust was the main contribution in the wet season. The high carcinogenic risks in the dry season correlate with more harmful air conditions during this season. Thus, it is important to control biomass burning to reduce air-pollution-related health risks during the dry season in northern Thailand.

A method is presented for determining monohydroxy polycyclic aromatic hydrocarbons (OHPAHs) having 2-, 3- and 4-rings in human urine by using high-performance liquid chromatography with fluorescence detection. A urine sample containing conjugates of OHPAHs was hydrolysed in the presence of β-glucuronidase/aryl sulfatase and the solution was cleaned up with a solid-phase extraction (C18 and silica). Eight OHPAHs, namely 1- and 2-hydroxynaphthalenes, 2-hydroxyfluorene, 2-, 3- and 4-hydroxyphenanthrenes, 3-hydroxyfluoranthene and 1-hydroxypyrene, were separated and 1- and 9-hydroxyphenanthrenes co-eluted on an alkylamide-type reversed-phase column with fluorimetric detection. The urinary concentrations of OHPAHs were quantified by using deuterated 1-hydoxypyrene as an internal standard. The method showed good repeatability for inter- and intra-day precisions as well as good linearity of calibration curves (r 2 ranged from 0.996 to 0.999). The limits of detection (S/N=3) were in the range from 2.3 fmol to 2.2 pmol per injection. This method was successfully applied to urine samples from non-smoking taxi drivers, traffic policemen and rural villagers of Chiang Mai, Thailand. The results showed higher urinary concentrations of OHPAHs in rural villagers, consistent with higher respiratory exposure to PAHs.