济南市城市扬尘的微观形貌和化学组分特征分析

Micromorphology Characteristics and Chemical Composition of Urban Dust in Ji’nan

城市扬尘作为大气颗粒物的主要来源之一,对环境空气质量的影响较大。为探究济南市不同区域城市扬尘物理特性、微观形貌和化学组分的季节变化特征,采集了济南市有代表性的四个区域(钢铁集聚区、城郊结合部、市区和县区)2021年不同季节的扬尘样品,分析了扬尘的比表面积、微观形貌、化学组分的变化特征。结果表明,春季扬尘颗粒粒径较小,比表面积较大;钢铁集聚区PM_(2.5)占比最高,为5.26%,比表面积为351.3 m^(2)·kg^(-1);其次为市区PM_(2.5)占比较高,为3.49%,比表面积为247.5 m^(2)·kg^(-1)。扫描电镜结果显示钢铁集聚区和市区扬尘颗粒主要有规则的“块状”“簇状”“片状”的矿物颗粒、不规则的“链状”和“蓬松状”的烟尘集合体以及“球状”燃煤飞灰颗粒,钢铁集聚区链状密集的烟尘集合体主要来源于机动车尾气和燃煤,市区聚合蓬松状烟尘集合体主要来源于机动车尾气;春季矿物颗粒比例较大,冬季密集链状烟尘集合体和燃煤飞灰较多,主要来源于机动车尾气和燃煤,其他季节聚合蓬松状烟尘集合体较多,主要来源于机动车尾气。各区域扬尘PM_(2.5)中水溶性离子Ca^(2+)、SO_(4)^(2-)和Na^(+)含量较高。4个区域中各季节AE/CE值均小于1,说明济南市扬尘PM_(2.5)呈碱性,市区冬季的AE/CE最高为0.36。扬尘PM_(2.5)中碳组分均以O_(C)为主,济南市各区域扬尘中O_(C)/E_(C)比值在5.4-17.5之间,均存在明显的二次有机碳的生成,且碳组分主要来自于燃煤和生物质燃烧排放。扬尘PM_(2.5)中金属元素Si、Al和Fe含量较高,主要受土壤风沙、燃煤和钢铁冶炼影响。

Ji’nan,the economic,political and cultural center of Shandong Province,is one of the“2+26”cities in the Beijing-Tianjin-Hebei air pollution transmission channel.Urban dust is one of main sources of atmospheric particulate matters and influences ambient air quality greatly.The dust samples in different seasons in 2021 from four representative regions of Jinan(steel agglomeration area,suburban junction,urban area and county area)were collected to explore the seasonal variation characteristics of urban dust.Specific surface area,microscopic morphology and chemical composition of the dust were analyzed and the results showed that the particle size of dust in spring was smaller and the specific surface area was larger.The dust from steel agglomeration area had the highest PM_(2.5) ratio(5.26%)and specific surface area(351.3 m^(2)·kg^(-1)).PM_(2.5) in urban area accounted for 3.49%,and that in the specific surface area was 247.5 m^(2)·kg^(-1).Scanning electron microscopy results showed that the dust in the steel agglomeration area consisted of mainly regular“block-like”,“cluster-like”,“flaky”mineral particles,irregular“chain-shaped”and“fluffy”soot aggregates,and“spherical”coal-fired fly ash particles.In this area,the dense chain soot aggregates mainly came from motor vehicle exhaust and coal burning,while the aggregates in the urban area almost only came from motor vehicle exhaust.In spring,the proportion of mineral particles was large.In winter,dense chain soot aggregates and coal-burning fly ash dominated and mainly came from motor vehicle exhaust and coal-burning.There were more aggregated fluffy soot aggregates in other seasons.The contents of water-soluble ions Ca^(2+),SO_(4)^(2−)and Na^(+)in PM_(2.5) of dust in various regions were high.In the four regions,the AE/CE values in each season were less than 1,indicating that the PM_(2.5) of dust in Jinan was alkaline,especially the winter AE/CE in the urban was no more than 0.36.The carbon components in the PM_(2.5) of dust were mainly O_(C).The ratio of O_(C)/E_(C) in the dust of Jinan was between 5.35–17.47 with highly possible secondary organic carbon generation occurring.The carbon components mainly came from coal combustion and biomass combustion emissions.The metal elements,Si,Al,and Fe content,in the PM_(2.5) of dust were higher,indicating that it was mainly affected by soil,wind,sand,coal burning and steel smelting.