Abstract
ABSTRACTImpact of traditional biomass burning activities on regional air quality is a major environmental concern. Measurement campaigns were performed during post-harvesting activities in the Ba Vi region in Hanoi in May–June of 2015 and 2016. To quantify the source for regional haze the sampling of rice straw burning emissions was performed on fields. Carbonaceous (OC, EC, BrC) fractions, heavy metals, organic and ionic composition, and microstructure were characterized. A set of functionalities (hydroxyl, aliphatic, carbonyl, carboxylate, and nitro groups) revealed a functional marker of pile combustion. Optical, microstructural, and chemical analyses of environmentally-dangerous pollutants from traffic and cooking sources provided characteristics and functional markers of different pollution sources. Chemical features of rice straw burning were identified on the Ba Vi site during the haze episode of 2015, when PM10 mass approached the high smoke intensity, up to 167 µg m–3. Small-scale meteorology affected PM10, OC and EC, and ion mass in days of highest relative humidity and fogs. In days of highest smoke OC dominated PM10 mass by up to 42%, the OC/EC ratio approached 20, in line with observations of mainly smoldering emissions across the fields. Spectral features of regional haze smoke demonstrated the absorption of rice straw burning whereas the impact of biogenic, traffic, and cooking sources were significantly lower. Individual particle analyses showed carbonaceous particles internally/externally mixed with inorganic fly ash and dust. Smoke micromarkers revealed the microstructure of regional aerosols representative for Southeast Asia in BB periods. Significantly lower PM10 mass concentrations and strong difference in aerosol composition before post-harvesting activities suggested that agricultural burning represents a large contribution to air quality degradation in the rural area of Vietnam.
Highlights
Combustion has been increasingly recognized as the most important source of environmentally-active aerosols, containing black carbon (BC), organic carbon (OC), and inorganic fly ash
During controlled field burning of rice straw somewhat smaller OC/elemental carbon (EC) ratios of 10 ± 2 and 5.8 ± 3.2 were obtained by Engling et al (2009) and Oanh et al (2011), respectively
Chemical characterization of ambient aerosols in the Ba Vi region during a haze period in the post-harvest burning season shows a predominant impact of biomass burning on the ambient PM10 mass and its constituents
Summary
Combustion has been increasingly recognized as the most important source of environmentally-active aerosols, containing black carbon (BC), organic carbon (OC), and inorganic fly ash They impact directly and indirectly on the Earth’s radiation balance, cloudiness, and subsequently affect the regional and global climate (Ramanathan and Carmichael, 2008). Low EC levels indicate that smoldering emissions were dominant during the entire sampling period. The OC/EC ratios in PM10 were above 7.5 and as high as 20 during sampling period, with the highest value observed on the same day (7 June) when EC emissions were radically suppressed (Fig. 10(b)). Remembering that high OC/EC ratios are characteristic for on-field emissions (Table 1), it can indicate that smoldering fires, dominated by high OC, prevailed during the smoke period in the Ba Vi region. Meteorological conditions (low wind speed, high temperatures and strong solar radiation) could favor formation of secondary organic aerosols due to condensation of heavier hydrocarbons generated by acid-catalyzed oxidation and photochemical reactions in the smoke plume (Alves et al, 2010), that could have influenced high daily OC/EC ratios as well
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