Wintertime organic and inorganic aerosols in Lanzhou, China: sources, processes, and comparison with the results during summer
Wintertime organic and inorganic aerosols in Lanzhou, China: sources, processes, and comparison with the results during summer
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中国兰州冬季有机和无机气溶胶：来源、过程及其与夏季结果的比较
DOI：
10.5194/acp-16-14937-2016
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发表时间：
2016
影响因子：
6.3
通讯作者：
Qin Dahe
中科院分区：
文献类型：
--
作者：
Xu Jianzhong;Shi Jinsen;Zhang Qi;Ge Xinlei;Canonaco Francesco;Prevot Andre S. H.;Vonwiller Matthias;Szidat Sonke;Ge Jinming;Ma Jianmin;An Yanqing;Kang Shichang;Qin Dahe
抽象的。兰州位于中国西部陡峭的高山峡谷中，是中国冬季污染最严重的城市之一。在这项研究中，一个Aerodyne高分辨率飞行时间气溶胶质谱仪（HR-ToF-AMS），一个七波长aethalometer，和一个扫描迁移率粒度仪（SMPS）部署在2014年1月10日至2月4日，研究质量浓度，化学过程和亚微米颗粒物（PM 1）的来源。在这项研究期间，PM 1的平均浓度为57.3 µg m−3（每小时平均浓度范围为2.1至229.7 µg m−3），其中有机气溶胶（OA）占51.2%，其次是硝酸盐（16.5%），硫酸盐（12.5%），铵（10.3%），黑碳（BC，6.4%）和氯化物（3.0%）。冬季PM 1的质量浓度是2012年夏季在同一地点观测到的平均值（24.5 µg m−3）的两倍多，但OA的质量分数在两个季节相似。硝酸盐在冬季对PM 1质量的贡献明显高于夏季（16.5%比10%），这主要是由于在低气温下更有利于颗粒相的分配。随着PM 1总质量负荷的增加，有机酸和硝酸盐的质量分数均增加了1.5%（有机酸为47 ~ 52，硝酸盐为13 ~ 18%），而硫酸盐的平均质量分数则减少了6%（17 ~ 11%），表明有机酸和硝酸盐在兰州市空气重污染事件中的重要性. OA、硝酸盐、硫酸盐、铵和氯化物的粒径分布都在0.500 nm处达到峰值，OA稍宽，表明冬季气溶胶颗粒内部混合，这可能是由于兰州冬季经常出现平静和停滞的空气条件（平均风速：0.82 m s−1）。OA的平均质谱显示中等氧化程度（平均O scinC比为0.28），低于2012年夏季的氧化程度（O scinC = 0.33）。这与冬季较弱的光化学处理相一致。正矩阵分解（PMF）与多线性引擎（ME-2）求解器确定了六个OA源，即，类烃OA（HOA）、生物质燃烧OA（BBOA）、烹饪排放OA（COA）、煤燃烧OA（CCOA）和两个含氧OA（OOA）因子。其中一种OOA氧化程度较低（LO-OOA），另一种氧化程度较高（MO-OOA）。LO-OOA是含量最丰富的OA成分（占OA质量的22.3%），其次是CCOA（22.0%）、COA（20.2%）、MO-OOA（14.9%）、BBOA（10.8%）和HOA（9.8%）。PM高污染时段，兰州市大气一次源（= HOA + BBOA + COA + CCOA）的质量分数增加，说明本地一次源排放是兰州市冬季大气污染事件形成的主要原因。对本研究中的4个PM2.5过滤器样品进行放射性碳（14 C）测量，从而可以对有机碳（OC）进行定量源解析。非化石污染源平均占有机碳的55 ± 3%，主要来源于生物质燃烧和炊事活动，说明非化石污染源对兰州市大气颗粒物污染的重要性。结合PMF结果，我们还发现大部分（66 ± 10%）的次生OC来自非化石OC。
Abstract. Lanzhou, which is located in a steep alpine valley in western China, is one of the most polluted cities in China during the wintertime. In this study, an Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS), a seven-wavelength aethalometer, and a scanning mobility particle sizer (SMPS) were deployed during 10 January to 4 February 2014 to study the mass concentrations, chemical processes, and sources of submicrometer particulate matter (PM1). The average PM1 concentration during this study was 57.3 µg m−3 (ranging from 2.1 to 229.7 µg m−3 for hourly averages), with organic aerosol (OA) accounting for 51.2 %, followed by nitrate (16.5 %), sulfate (12.5 %), ammonium (10.3 %), black carbon (BC, 6.4 %), and chloride (3.0 %). The mass concentration of PM1 during winter was more than twice the average value observed at the same site in summer 2012 (24.5 µg m−3), but the mass fraction of OA was similar in the two seasons. Nitrate contributed a significantly higher fraction to the PM1 mass in winter than summer (16.5 % vs. 10 %), largely due to more favored partitioning to the particle phase at low air temperature. The mass fractions of both OA and nitrate increased by ∼ 5 % (47 to 52 for OA and 13 to 18 % for nitrate) with the increase of the total PM1 mass loading, while the average sulfate fraction decreased by 6 % (17 to 11 %), indicating the importance of OA and nitrate for the heavy air pollution events in Lanzhou. The size distributions of OA, nitrate, sulfate, ammonium, and chloride all peaked at ∼ 500 nm, with OA being slightly broader, suggesting that aerosol particles were internally mixed during winter, likely due to frequently calm and stagnant air conditions during wintertime in Lanzhou (average wind speed: 0.82 m s−1). The average mass spectrum of OA showed a medium oxidation degree (average O ∕ C ratio of 0.28), which was lower than that during summer 2012 (O ∕ C = 0.33). This is consistent with weaker photochemical processing during winter. Positive matrix factorization (PMF) with the multi-linear engine (ME-2) solver identified six OA sources, i.e., a hydrocarbon-like OA (HOA), a biomass burning OA (BBOA), a cooking-emitted OA (COA), a coal combustion OA (CCOA), and two oxygenated OA (OOA) factors. One of the OOAs was less oxidized (LO-OOA), and the other one more oxidized (MO-OOA). LO-OOA was the most abundant OA component (22.3 % of OA mass), followed by CCOA (22.0 %), COA (20.2 %), MO-OOA (14.9 %), BBOA (10.8 %), and HOA (9.8 %). The mass fraction of primary OA ( = HOA + BBOA + COA + CCOA) increased during high PM pollution periods, indicating that local primary emissions were a main reason for the formation of air pollution events in Lanzhou during winter. Radiocarbon (14C) measurement was conducted on four PM2.5 filter samples from this study, which allowed for a quantitative source apportionment of organic carbon (OC). The non-fossil sources on average accounted for 55 ± 3 % of OC, which could be mainly from biomass burning and cooking activities, suggesting the importance of non-fossil sources for the PM pollution in Lanzhou. Together with the PMF results, we also found that a large fraction (66 ± 10 %) of the secondary OC was from non-fossil OC.