关中典型城市及农村夏季PM2.5的化学组成对比

于2016年7~8月采集了陕西省西安市（城市）及蔺村（农村）夏季昼夜PM_2.5样品，分析其有机碳（OC）、元素碳（EC）和无机离子等化学组分的含量，探讨关中平原城市和农村地区PM_2.5的化学组成和来源的差异.结果表明，采样期间西安和蔺村的PM_2.5浓度分别为（49.7±22.8）和（62.6±14.2）μg/m³.西安PM_2.5中OC和EC的浓度（6.5±2.5）μg/m³，（3.2±1.8）μg/m³]与蔺村（6.8±1.8）μg/m³，（3.8±2.3）μg/m³]相当.西安OC/EC比值白天（2.6）高于夜晚（1.9），蔺村反之（白天：1.6；夜晚：2.7），主要是因为夜间城市地区重型卡车运输活动增强导致排放更多EC，而夜间农村地区人为活动较少导致EC排放显著降低.西安和蔺村无机离子总浓度分别为（20.2±14.6）和（30.1±10.5）μg/m³，占PM_2.5浓度的40.6%和47.6%.蔺村SO₄^2-的平均浓度高达19.0μg/m³，占PM_2.5浓度的30%以上，远高于西安（9.4μg/m³和18.9%），主要与农村固体燃料（煤和生物质）使用有关.西安NO₃^-和Ca²⁺的浓度及其对PM_2.5的贡献、NO₃^-/SO₄^2-比值均明显大于蔺村，表明城市地区受机动车尾气和扬尘的影响更大.西安K⁺与Ca²⁺和Mg²⁺的相关性较强，而蔺村K⁺与EC的相关性显著强于西安，说明西安市区K⁺由粉尘源主导，而农村地区则主要来自生物质燃烧.

Comparison on the chemical composition of PM2.5 in the urban and rural regions of Guanzhong plain,China

PM_2.5 samples were collected on a day/night basis at an urban site in Xi'an in July 2016 and at Lin Village, a rural site 80km northeast to Xi'an, in August 2016. The samples were determined for organic carbon (OC), elemental carbon (EC), and inorganic ions to investigate the differences in chemical compositions and sources of PM_2.5 between the urban and rural areas of Guanzhong Plain. The results showed that PM_2.5 in Xi'an and Lin Village during the sampling period were (49.7±22.8)μg/m³ and (62.6±14.2)μg/m³, respectively. Concentrations of OC and EC in PM_2.5 were similar between Xi'an(6.5±2.5)μg/m³ and (3.2±1.8)μg/m³] and Lin Village(6.8±1.8)μg/m³ and (3.8±2.3)μg/m³]. The OC/EC mass ratios in Xi'an were higher in the daytime (2.6) than in the nighttime (1.9), in contrast to those in Lin Village, which were lower in the daytime (1.6) and higher in the nighttime (2.7). Such diurnal differences can be explained by an enhanced emission of EC due to the nighttime occurrence of heavy-duty trucks in the urban area and a decreased emission of EC due to the nighttime absence of anthropogenic activities (e.g., biomass burning and coal combustion) in the rural area. Inorganic ions of PM_2.5 were (20.2±14.6)μg/m³ and (30.1±10.5)μg/m³ in Xi'an and Lin Village and accounted for 40.6% and 47.6% of PM_2.5 in the two regions, respectively. SO₄^2- of PM_2.5 in the rural area was 19.0μg/m³ and accounted for one-third of the fine particle mass, which was much higher than that in Xi'an (9.4μg/m³ and 18.9%). Concentrations of NO₃^- and Ca²⁺ in Xi'an, their masses relative to PM_2.5 and NO₃^-/SO₄^2- mass ratio were significantly higher than those in Lin Village, suggesting that the urban atmosphere was more affected by motor vehicle exhausts and emissions from road-dust and construction activities. K⁺ in the samples showed stronger correlations with Ca²⁺ and Mg²⁺ in Xi'an due to the dominant source of dust. In contrast, K⁺ was correlated with EC in the rural area, mainly due to the dominance of biomass burning emissions.