洛阳地区碳质组分季节特征及来源解析:棕碳的重要贡献

Seasonal Variations and Source Apportionment of Carbonaceous Components in Luoyang:Implication for Brown Carbon Contribution

为探究洛阳地区碳质气溶胶尤其是棕碳的季节、污染特征及其来源解析,于2018~2019年的四季共采集到98个样品,并分析了碳质气溶胶浓度特征和光学特性.4个季节ρ[有机碳(OC)]和ρ[元素碳(EC)]介于(7.04±1.82)~(23.81±8.68)μg·m^(-3)和(2.96±1.4)~(13.41±7.91)μg·m^(-3),呈现冬高夏低的季节变化趋势;与2015年相比,碳质组分的占比升高了8.33%~141.03%,二次有机气溶胶占比(SOC/OC)升高了0.77%~63.14%.碳质气溶胶光吸收截面(MAC)值与碳质组分的浓度呈现出不同的季节变化,秋季(7.67m^(2)·g^(-1))>冬季(5.65 m^(2)·g^(-1))>春季(5.13m^(2)·g^(-1))>夏季(3.84m^(2)·g^(-1)),445 nm处的MAC值(3.84~7.67m^(2)·g^(-1))明显低于新产生煤灰值.棕碳的光吸收和其占总光吸收的贡献值(babs,BrC,405 nm,babs,BrC,405 nm/babs,405 nm)的季节变化为冬季(31.57 Mm-1,33%)、秋季(11.40 Mm-1,25%)、春季(4.88 Mm-1,23%)和夏季(2.12 Mm-1,21%),在污染过程中,碳质组分占比在降低,而babs,BrC,405 nm/babs,405 nm变化相反,强调棕碳对总光吸收的重要贡献.综合PMF结果和babs,BrC,405 nm与PM_(2.5)组分的相关系数的结果,机动车和二次硝酸盐分别贡献了27.7%和24.0%.研究结果为洛阳地区碳质气溶胶,尤其在棕碳的深度治理提供了科学依据.

A total of 98 samples were collected to analyze the seasonal variation and source apportionment of carbonaceous components,especially brown carbon(BrC),of PM_(2.5)in Luoyang during 2018-2019.The concentrations of organic carbon(OC)and elemental carbon(EC)ranged from(7.04±1.82)μg·m^(-3)to(23.81±8.68)μg·m^(-3)and(2.96±1.4)μg·m^(-3)to(13.41±7.91)μg·m^(-3),respectively,showing the seasonal variation of being high in winter and low in summer;the carbonaceous fraction and secondary organic aerosol percentages were higher by 8.33%-141.03%and by 0.77%-63.14%,respectively,compared with that in 2015.The light absorption cross section(MAC)values showed different seasonal variations with the concentration of carbonaceous fraction,shown in descending order as autumn(7.67 m~2·g^(-1))>winter(5.65 m~2·g^(-1))>spring(5.13 m~2·g^(-1))>summer(3.84 m~2·g^(-1)).The MAC values ranged from 3.84 to 7.67 m~2·g^(-1)at 445 nm,which was lower than that in coal ash.Seasonal variation in light absorption and the contribution of BrC to total light absorption(babs,BrC,405 nm,babs,BrC,405 nm/babs,405 nm)in descending order was winter(31.57 Mm-1,33%),autumn(11.40 Mm-1,25%),spring(4.88 Mm-1,23%),and summer(2.12 Mm-1,21%).The proportion of carbonaceous components decreased as haze episodes evolved,whereas the contribution of light absorption of BrC increased,highlighting the important contribution of BrC to the total light absorption.The results of PMF and correlation coefficients of babs,BrC,405 nmand PM_(2.5)components indicated that motor vehicles and secondary nitrate contributed 27.7%and 24.0%,respectively.Our findings have significant scientific implications for the deep controlling of carbonaceous aerosol,especially for BrC,in Luoyang in the future.