Ambient air quality in the Kathmandu Valley, Nepal, during the pre-monsoon: concentrations and sources of particulate matter and trace gases
Ambient air quality in the Kathmandu Valley, Nepal, during the pre-monsoon: concentrations and sources of particulate matter and trace gases
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DOI：
10.5194/acp-20-2927-2020
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发表时间：
2020-03-11
影响因子：
6.3
通讯作者：
Stone, Elizabeth A.
中科院分区：
文献类型：
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作者：
Islam, Md Robiul;Jayarathne, Thilina;Stone, Elizabeth A.
尼泊尔的加德满都山谷是一个碗状的城市盆地，那里的空气污染严重，对350万居民的健康构成威胁。作为尼泊尔环境监测和源测试实验（NAMaS 1E）的一部分，于2015年4月11日至24日在季风前季节对加德满都谷地的环境空气质量进行了调查。在靠近山谷中心的半城市位置，对细颗粒物和粗颗粒物（分别为PM2.5和PM10）、在线PM1、无机微量气体（NH3、HNO3、SO2和HCI）和含碳气体（CO2、CO、CH4和93种非甲烷挥发性有机化合物；NMVOCs）的环境浓度进行了量化。NMVOC的浓度和比例表明，其主要来源是维护不良的车辆排放、生物质燃烧和溶剂/汽油蒸发。在这两周内，PM2.5的日平均浓度在30至207 μ g（-3）之间，超过了世界卫生组织24小时标准的1.2至8.3倍。平均而言，PM2.5的非水质量由有机物（48%）、元素碳（13%）、硫酸盐（16%）、硝酸盐（4%）、铵（9%）、氯化物（2%）、钙（1%）、镁（0.05%）和钾（1%）组成。温度和相对湿度的较大日变化导致气溶胶液态水含量、NH3、HNO3和HCI的气-气溶胶相分配以及气溶胶溶液ph的相应变化。气相卤素的观测水平表明，涉及Cl和Br的多相卤素自由基化学影响了区域空气质量。为了深入了解有机碳（OC）的来源，对一次和二次来源的分子标记进行了量化。左旋葡萄糖聚糖（平均1230 +/- 1154 ng m(-3)）、1,3,5-三苯基苯（0.8 +/- 0.6 ng m(-3)）、胆固醇（2.9 +/- 6.6 ng m(-3)）、豆甾醇（1.0 +/- 0.8 ng m(-3)）和顺式蒎酸（4.5 +/- 1.9 ng m(-3)）分别表明生物质燃烧、垃圾燃烧、食物烹饪、牛粪燃烧和单萜烯二次有机气溶胶的贡献。利用NAMaS 1E中开发的源剖面，化学质量平衡（CMB）源分配模型用于估计主要主要源对OC的贡献，包括垃圾燃烧（18 +/- 5%），生物质燃烧（17 +/- 10%），包括露天燃烧和生物质燃料炉灶，以及内燃机（汽油和柴油）发动机（18 +/- 9%）。对新开发的来源概况进行的模型敏感性测试表明，生物质燃烧的贡献在以前估计的2倍内，但垃圾燃烧的贡献更大（高达3倍），这表明垃圾燃烧对区域空气质量的潜在影响很大，需要进一步评估这一来源。二级有机碳（SOC）对PM2.5 OC的贡献包括：人为前体萘（10 +/- 4%）和甲基萘（0.3 +/- 0.1%）和生物前体单萜（0.13 +/- 0.07%）和倍半萜（5 +/- 2%）。平均25%的PM2.5 OC未分配，表明存在其他来源（例如，蒸发和/或工业排放，如砖窑、食品烹饪和其他类型的有机碳）和/或低估了已确定来源类型的贡献。来源解析结果表明，人为燃烧源（包括生物质燃烧、垃圾燃烧和化石燃料燃烧）是PM2.5的最大贡献者，因此应将其视为控制环境PM污染的主要目标。
The Kathmandu Valley in Nepal is a bowl-shaped urban basin that experiences severe air pollution that poses health risks to its 3.5 million inhabitants. As part of the Nepal Ambient Monitoring and Source Testing Experiment (NAMaS 1E), ambient air quality in the Kathmandu Valley was investigated from 11 to 24 April 2015, during the premonsoon season. Ambient concentrations of fine and coarse particulate matter (PM2.5 and PM10, respectively), online PM1, inorganic trace gases (NH3, HNO3, SO2, and HCI), and carbon-containing gases (CO2, CO, CH4, and 93 nonmethane volatile organic compounds; NMVOCs) were quantified at a semi-urban location near the center of the valley. Concentrations and ratios of NMVOC indicated origins primarily from poorly maintained vehicle emissions, biomass burning, and solvent/gasoline evaporation. During those 2 weeks, daily average PM2.5 concentrations ranged from 30 to 207 mu g m(-3), which exceeded the World Health Organization 24 h guideline by factors of 1.2 to 8.3. On average, the nonwater mass of PM2.5 was composed of organic matter (48 %), elemental carbon (13 %), sulfate (16 %), nitrate (4 %), ammonium (9 %), chloride (2 %), calcium (1 %), magnesium (0.05 %), and potassium (1 %). Large diurnal variability in temperature and relative humidity drove corresponding variability in aerosol liquid water content, the gas-aerosol phase partitioning of NH3, HNO3, and HCI, and aerosol solution pH. The observed levels of gas-phase halogens suggest that multiphase halogen-radical chemistry involving both Cl and Br impacted regional air quality. To gain insight into the origins of organic carbon (OC), molecular markers for primary and secondary sources were quantified. Levoglucosan (averaging 1230 +/- 1154 ng m(-3)), 1,3,5-triphenylbenzene (0.8 +/- 0.6 ng m(-3)), cholesterol (2.9 +/- 6.6 ng m(-3)), stigmastanol (1.0 +/- 0.8 ng m(-3)), and cis-pinonic acid (4.5 +/- 1.9 ng m(-3)) indicate contributions from biomass burning, garbage burning, food cooking, cow dung burning, and monoterpene secondary organic aerosol, respectively. Drawing on source profiles developed in NAMaS 1E, chemical mass balance (CMB) source apportionment modeling was used to estimate contributions to OC from major primary sources including garbage burning (18 +/- 5 %), biomass burning (17 +/- 10 %) inclusive of open burning and biomass-fueled cooking stoves, and internal-combustion (gasoline and diesel) engines (18 +/- 9 %). Model sensitivity tests with newly developed source profiles indicated contributions from biomass burning within a factor of 2 of previous estimates but greater contributions from garbage burning (up to three times), indicating large potential impacts of garbage burning on regional air quality and the need for further evaluation of this source. Contributions of secondary organic carbon (SOC) to PM2.5 OC included those originating from anthropogenic precursors such as naphthalene (10 +/- 4 %) and methylnaphthalene (0.3 +/- 0.1 %) and biogenic precursors for monoterpenes (0.13 +/- 0.07 %) and sesquiterpenes (5 +/- 2 %). An average of 25 % of the PM2.5 OC was unapportioned, indicating the presence of additional sources (e.g., evaporative and/or industrial emissions such as brick kilns, food cooking, and other types of SOC) and/or underestimation of the contributions from the identified source types.The source apportionment results indicate that anthropogenic combustion sources (including biomass burning, garbage burning, and fossil fuel combustion) were the greatest contributors to PM2.5 and, as such, should be considered primary targets for controlling ambient PM pollution.