Emission from field burning of crop residue, a common practice in many parts of the world today, has potential effects on air quality, atmosphere and climate. This study provides a comprehensive size and compositional characterization of particulate matter (PM) emission from rice straw (RS) burning using both in situ experiments (11 spread field burning) and laboratory hood experiments (3 pile and 6 spread burning) that were conducted during 2003–2006 in Thailand. The carbon balance and emission ratio method was used to determine PM emission factors (EF) in the field experiments. The obtained EFs varied from field to hood experiments reflecting multiple factors affecting combustion and emission. In the hood experiments, EFs were found to be depending on the burning types (spread or pile), moisture content and the combustion efficiency. In addition, in the field experiments, burning rate and EF were also influenced by weather conditions, i.e. wind. Hood pile burning produced significantly higher EF (20±8 g kg−1 RS) than hood spread burning (4.7±2.2 g kg−1 RS). The majority of PM emitted from the field burning was PM2.5 with EF of 5.1±0.7 g m−2 or 8.3±2.7 g kg−1 RS burned. The coarse PM fraction (PM10-2.5) was mainly generated by fire attention activities and was relatively small, hence the resulting EF of PM10 (9.4±3.5 g kg−1 RS) was not significantly higher than PM2.5. PM size distribution was measured across 8 size ranges (from <0.4 μm to >9.0 μm). The largest fractions of PM, EC and OC were associated with PM1.1. The most significant components in PM2.5 and PM10 include OC, water soluble ions and levoglucosan. Relative abundance of some methoxyphenols (e.g., acetylsyringone), PAHs (e.g., fluoranthene and pyrene), organochlorine pesticides and PCBs may also serve as additional signatures for the PM emission. Presence of these toxic compounds in PM of burning smoke increases the potential toxic effects of the emission. For illustration, an estimation of the annual RS field burning in Thailand was made using the obtained in situ field burning EFs and preliminary burning activity data.
ABSTRACT:In Thailand and many other Asian countries, where rice is the major crop, open burning of rice straw after harvesting is a common practice. This activity releases a large amount of air pollutants, which can cause serious effects on the ambient air quality, public health and climate. In this study, the number of hotspots, which represents open fires, detected on the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite images over the Pathumthani were counted. The results show high numbers of hotspots during the rice straw burning season. Good correlation was obtained between hotspots numbers and the levels of air pollutants, including carbon monoxide and particulate matter, measured at the Rangsit ground based air quality monitoring station of the Pathumthani province. Forward trajectories were calculated using the HYbrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT4) model to roughly examine possible transport pathways of smoke emitted from the rice straw burning in Pathumthani. The results show that during the intensive burning season (November-April) smoke plumes from rice straw burning in Pathumthani can be transported to Bangkok following the Northeast monsoon. Emission from open rice straw burning therefore may contribute significantly to air pollution levels in the surrounding areas including Bangkok.
This study characterized the particulate matter (PM) pollution at a forest site in the Khao Yai (KY) National Park of Thailand, 700 m above sea level and 120 km upwind to Bangkok during the dry season. Two dichotomous samplers simultaneously operated on each monitoring day to collect 2 samples (on 2 filter types: quartz and mix cellulose) of 24 h PM 2.5 and 2 samples of 24 h PM 10-2.5 . More focus was on the dry and more polluted season with a longer sampling period (43 days: Jan-Feb 2005) and less on wet season (10 days, Jun 2005). Samples were analyzed for mass, water soluble ions, elements, EC and OC (Sunset analyzer). PM 2.5 levels obtained at KY in the dry period (47 µg m -3 ) were comparable to those in several urban areas in Southeast Asia, but the wet season levels (7 µg m -3 ) were significantly lower. In the dry season, levels of EC associated with PM 2.5 at KY were remarkably lower than but OC were comparable to those found in urban areas which resulted in considerably low EC/TC ratios (0.08). The major mass groups of PM 2.5 in the dry season were organic matter of biomass smoke origin (OM-smoke), secondary inorganic aerosol, organic matter of other origins than smoke (OM-others) and crustal. Similar contributors to PM 2.5 were also found in the wet season but with only a small contribution from biomass burning smoke. Significant contributions from distant sources to PM 2.5 levels measured at KY were also confirmed by the HYSPLIT backward trajectory analysis. The coarse fraction (PM 10-2.5 ) had major mass groups of OM-others, inorganic particles and crustal that were most likely related to local sources, and some amount of aged sea salt indicating a distant source origin.
TiO 2 doped with Fe 3? was prepared by an impregnation technique and its sonophotocatalytic activity over methyl orange (MO) was investigated. The Fe/ TiO 2 surface presented red shift to longer wavelength, resulting in a lower energy band gap. Fe loading of 0.1 wt% on TiO 2 provided the optimum degradation. The MO degradation rate constant under sonophotocatalytic conditions was 2.5 times higher than under photocatalytic conditions.
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