威海市环翠区2021—2022年大气PM_(2.5)化学组成季节变化特征

Seasonal Changes of Chemical Components of PM_(2.5)in Huancui District of Weihai City from 2021 to 2022

以威海市环翠区2021年6月至2022年5月一年中采样所得大气中PM_(2.5)的质量浓度日均值及其中水溶性离子(NO_(3)^(-)、SO_(4)^(2-)、NH_(4)^(+)、F^(-)、Cl^(-)、K^(+)、Na^(+)、Mg^(2+)和Ca^(2+))、碳组分(有机碳(OC)、元素碳(EC))及无机元素的监测数据为依据,分析了PM_(2.5)及其化学组分的季节变化特征。结果表明,威海市环翠区PM_(2.5)年均浓度为32μg·m^(-3),低于PM_(2.5)的国家空气质量标准二级限值,季节性特征明显,冬季最高,夏季最低,春季略高于秋季。PM_(2.5)中水溶性离子年均浓度为16.50μg·m^(-3),占PM_(2.5)总质量的51.6%,各水溶性离子浓度次序为:NO_(3)^(-)>SO_(4)^(2-)>NH_(4)^(+)>Na^(+)>Cl^(-)>Ca^(2+)>K^(+)>Mg^(2+)>F^(-);NO_(3)^(-)和NH_(4)^(+)浓度均表现为冬秋季较高,夏春季较低,SO_(4)^(2-)浓度夏季最高,其它季节浓度相差不大,其它离子的季节浓度除Na^(+)春季浓度最高外,均呈现出冬季最高的特征;NO_(3)^(-)、SO_(4)^(2-)与NH_(4)^(+)是其中的主要水溶性离子,不同季节这3种离子浓度之和的次序为:17.61μg·m^(-3)(冬季)>14.04μg·m^(-3)(秋季)>12.56μg·m^(-3)(春季)>11.48μg·m^(-3)(夏季);硫氧化率(SOR)、氮氧化率(NOR)的季节变化特征明显,基本表现为冬季>秋季>春季>夏季的趋势。PM_(2.5)的总碳(TC)和OC的季节变化趋势相同,二者各自的数据冬春季节接近,夏秋季节数据接近,但冬春季节明显高于夏秋季节;EC值除夏季较低外,其它3个季节的浓度相差不大。PM_(2.5)的无机元素主要有S、Si、K、Fe,少量Ca、Al、Na、Zn;对于同一种元素,大多表现为冬春季浓度较高,夏秋季较低,与PM_(2.5)浓度的季节变化基本一致;S元素冬春季浓度较低,夏秋季较高。PM_(2.5)中的已鉴别物种成分年平均浓度为23.7μg·m^(-3),占PM_(2.5)年平均浓度的74.0%,仍有26.0%的质量成分未能鉴别出来。

The daily mean mass concentrations of atmospheric PM_(2.5)and its water-soluble ions(NO_(3)^(-),SO_(4)^(2-),NH_(4)^(+),F^(-),Cl^(-),K^(+),Na^(+),Mg^(2+)and Ca^(2+)),carbon components(organic carbon(OC),elemental carbon(EC))and inorganic elements,in Huancui District of Weihai City from June 2021 to May 2022 were collected,and the seasonal variation characteristics of PM_(2.5)and its chemical components were analyzed.The results showed that the average annual concentration of PM_(2.5)in Huanchui District of Weihai City was 32μg·m^(-3),which was lower than the second-level limit of national air quality standard of PM_(2.5).The seasonal characteristics were obvious that the mass concentration was the highest concentration in winter,the lowest in summer,and slightly higher in spring than in autumn.The average annual concentration of water-soluble ions in PM_(2.5)was 16.50μg·m^(-3),accounting for 51.6%of the total mass of PM_(2.5),and the concentrations of water-soluble ions were ranked as:NO_(3)^(-)>SO_(4)^(2-)>NH_(4)^(+)>Na^(+)>Cl^(-)>Ca^(2+)>K^(+)>Mg^(2+)>F^(-).The concentrations of NO_(3)^(-)and NH_(4)^(+)were higher in winter and autumn,and lower in summer and spring.The concentration of SO_(4)^(2-)was the highest in summer,and there were no significant difference in other seasonal concentrations.The seasonal concentrations of other ions were the highest in winter,except for Na^(+),which was the highest in spring.NO_(3)^(-),SO_(4)^(2-)and NH_(4)^(+)were the main water-soluble ions.The sum of the concentrations of these three ions in different seasons was as following order:17.61μg·m^(-3)(winter)>14.04μg·m^(-3)(autumn)>12.56μg·m^(-3)(spring)>11.48μg·m^(-3)(summer).The seasonal variation characteristics of sulfur oxidation rate(SOR),nitrogen oxidation rate(NOR)were obvious,and the basic trend decreared in the following order:winter,autumn,spring and summer.The seasonal variation trends of total carbon(TC)and OC of PM_(2.5)were similar.The data of TC or OC were similar in winter and spring,and so were the data of summer and autumn,but the concentrations of EC in winter and spring were significantly higher than that in summer and autumn.The concentrations of EC in the other three seasons were similar except that the concentration of EC in summer was lower.The inorganic elements of PM_(2.5)mainly included S,Si,K and Fe,and a small amount of Ca,Al,Na and Zn.For the same element,the concentration was higher in winter and spring,and lower in summer and autumn,which was basically consistent with the seasonal variation of PM_(2.5) concentration.The concentrations of S element were low in winter and spring,but high in summer and autumn.The annual average concentration of identified species in PM_(2.5) was 23.7μg·m^(-3),accounting for 74.0%of the annual average concentration of PM_(2.5),and 26.0%of the mass components could not be identified.