A comprehensive assessment of fine particulate matter (PM2.5) compositions during the Southeast Asia dry season is presented. Samples of PM2.5 were collected between 24 June and 14 September 2014 using a high‐volume sampler. Water‐soluble ions, trace species, rare earth elements, and a range of elemental carbon (EC) and organic carbon were analyzed. The characterization and source apportionment of PM2.5 were investigated. The results showed that the 24 h PM2.5 concentration ranged from 6.64 to 68.2 µg m−3. Meteorological driving factors strongly governed the diurnal concentration of aerosol, while the traffic in the morning and evening rush hours coincided with higher levels of CO and NO2. The correlation analysis for non sea‐salt K+‐EC showed that EC is potentially associated with biomass burning events, while the formation of secondary organic carbon had a moderate association with motor vehicle emissions. Positive matrix factorization (PMF) version 5.0 identified the sources of PM2.5: (i) biomass burning coupled with sea salt [I] (7%), (ii) aged sea salt and mixed industrial emissions (5%), (iii) road dust and fuel oil combustion (7%), (iv) coal‐fired combustion (25%), (v) mineral dust (8%), (vi) secondary inorganic aerosol (SIA) coupled with F− (15%), and (vii) motor vehicle emissions coupled with sea salt [II] (24%). Motor vehicle emissions, SIA, and coal‐fired power plant are the predominant sources contributing to PM2.5. The response of the potential source contribution function and Hybrid Single‐Particle Lagrangian Integrated Trajectory backward trajectory model suggest that the outline of source regions were consistent to the sources by PMF 5.0.

Multiaxis differential optical absorption spectroscopy (MAX‐DOAS) observations were performed for the first time in Thailand at the rural site of Phimai (15.18°N, 102.56°E). Vertical profiles of eight components were retrieved separately using the Japanese MAX‐DOAS profile retrieval algorithm, version 2. Here we focused on formaldehyde (HCHO) and glyoxal (CHOCHO) and evaluated their volume mixing ratios in the lowest layer (0–1 km) of the retrieved vertical profiles. We estimated the ratio of CHOCHO to HCHO concentrations (RGF), which has been suggested to be an important tracer indicative of changes in volatile organic compound emissions. Higher HCHO and CHOCHO concentrations were observed during the dry season, reflecting the influence of biomass burning. The mean RGF for the Phimai site was estimated to be 0.032 ± 0.005. The estimated RGF for the dry season (0.028 ± 0.002) was lower than that during the wet season (0.040 ± 0.003), when biogenic emissions were dominated. While Phimai can be characterized as an environment with low nitrogen dioxide (NO2) concentrations (<1 ppbv), the potential impact of biomass burning on the lower RGF during the dry season was investigated by the occasional enhancement of NO2 concentrations as a tracer of biomass burning.

No abstract

Since January 2017 continuous multi-axis differential optical absorption spectroscopy (MAX-DOAS) observations have been performed for the first time at Pantnagar (29.03°N, 79.47°E), a semi-urban site located in the Indo-Gangetic Plain region in India.Here we report the formaldehyde (HCHO), glyoxal (CHOCHO), and nitrogen dioxide (NO 2 ) concentrations for the lowest layer (0−1 km) of the retrieved vertical profiles. The ratio of CHOCHO to HCHO concentrations (R GF ), an important tracer indicative of changes in volatile organic compound emissions was estimated. During spring and autumn enhanced concentrations of HCHO and CHOCHO were observed under the influence of biomass burning. The mean R GF for the whole observation period (January-November) in Pantnagar was estimated to be 0.029 ± 0.006. Comparing with similar MAX-DOAS observations in central Thailand and reported literature values, we found that the R GF tends to be < ~0.04 under the influence of biomass burning and/or anthropogenic emissions. (Citation: Hoque, H. M. S., H. Irie, A. Damiani, P. Rawat, and M. Naja, 2018: First simultaneous observations of formaldehyde and glyoxal by MAX-DOAS in the Indo-Gangetic Plain region. SOLA, 14, 159−164,

Ground-based remote sensing using multi-axis differential optical absorption spectroscopy (MAX-DOAS) was used to conduct continuous simultaneous observations of ozone (O3), nitrogen dioxide (NO2), and formaldehyde (HCHO) concentrations at Chiba (35.63° N, 140.10° E, 21 m a.s.l.) and Tsukuba (36.06° N, 140.13° E, 35 m a.s.l.), Japan, for 7 years from 2013 to 2019. These are urban and suburban sites, respectively, in the greater Tokyo metropolitan area. NO2 and HCHO are considered to be proxies for nitrogen oxides (NOx) and volatile organic compounds (VOCs), respectively, both of which are major precursors of tropospheric O3. The mean concentrations below an altitude of 1 km were analyzed as planetary boundary layer (PBL) concentrations. For a more spatially representative analysis around the urban area of Chiba, four MAX-DOAS instruments directed at four different azimuth directions (north, east, west, and south) were operated simultaneously and their data were unified. During the 7-year period, the satellite observations indicated an abrupt decrease in the tropospheric NO2 concentration over East Asia, including China. This suggested that the transboundary transport of O3 originating from the Asian continent was likely suppressed or almost unchanged during the period. Over this time period, the MAX-DOAS observations revealed the presence of almost-constant annual variations in the PBL O3 concentration, whereas reductions in NO2 and HCHO concentrations occurred at rates of approximately 6–10%/year at Chiba. These changes provided clear observational evidence that a decreasing NOx concentration significantly reduced the amount of O3 quenched through NO titration under VOC-limited conditions in the urban area. Under the dominant VOC-limited conditions, the MAX-DOAS-derived concentration ratio of HCHO/NO2 was found to be below unity in all months. Thus, the multi-component observations from MAX-DOAS provided a unique data set of O3, NO2, and HCHO concentrations for analyzing PBL O3 variations.