冬季南京城区气溶胶化学组分和吸湿性观测

Observation on the Chemical Composition and Hygroscopicity of Aerosols in Nanjing Urban Area in Winter

大气气溶胶的吸湿特性改变了颗粒物的粒径、光学性质、云凝结核活性,进而对大气能见度、地面辐射强迫和人体健康产生重要影响。针对长三角腹地城市南京重污染天气频发现象,笔者使用吸湿串联电迁移差分分析仪(H-TDMA)结合在线气体组分及气溶胶监测系统(MARGA)和相关气象数据对冬季南京城区气溶胶吸湿增长特性进行外场观测研究。结果表明:灰霾期间SO^(2-)_(4)、NO^(-)_(3)、NH^(+)_(4)的质量浓度分别为(17.57±9.07)(26.16±11.39)(13.61±6.68)μg/m^(3),非灰霾期间为(9.62±3.58)(12.12±7.51)(5.78±3.59)μg/m^(3),前者是后者的2倍。水溶性组分质量浓度大小依次为NO^(-)_(3)>SO^(2-)_(4)>NH^(+)_(4)>Cl^(-)>K^(+)>Ca^(2+)>Na^(+)>Mg^(2+)。其中NO^(-)_(3)的贡献最大,占PM_(2.5)的29%,其次是SO^(2-)_(4)占14%,NH^(+)_(4)占8%。其他水溶性组分(Cl^(-)、K^(+)、Ca^(2+)、Na^(+)、Mg^(2+))约占PM_(2.5)的5.9%。SO^(2-)_(4)、NO^(-)_(3)、NH^(+)_(4)的质量浓度没有明显日变化且保持在较高水平。观测期间气溶胶的不同粒径段粒子吸湿增长因子概率密度分布(GF-PDF)均呈双峰,随粒径增大,强吸湿组粒子的吸湿性增大,而弱吸湿组的吸湿性减弱。其中,40 nm粒径段粒子强、弱吸湿增长因子分别为1.335±0.03和1.054±0.008,80 nm粒径段为1.348±0.03和1.053±0.011,40 nm较80 nm粒径段的粒子弱吸湿峰更为明显。灰霾期间粒子的吸湿增长因子分别为1.307±0.08和1.413±0.07,非灰霾期间为1.230±0.03和1.300±0.03。冷锋过境时气溶胶弱吸湿组谱分布没有明显的变化,强吸湿组谱分布明显向弱吸湿方向偏移,吸湿性减弱。灰霾期间和整个观测期间PM_(2.5)的平均质量浓度分别为(87.56±25.87)(69.31±28.75)μg/m^(3),灰霾期间主要的二次气溶胶质量浓度占PM_(2.5)的66%,而粒子的平均吸湿增长因子从1.325±0.03降低到1.301±0.07。特殊时段春节期间弱吸湿组粒子的吸湿性增大,而强吸湿组粒子的吸湿性减弱。其中110 nm粒径段粒子强吸湿组吸湿增长因子明显下降,SO^(2-)_(4)、NO^(-)_(3)、NH^(+)_(4)的质量浓度也发生明显下降,吸湿增长因子和水溶性化学组分的变化呈良好一致性。

The hygroscopicity of aerosol particles change the particle sizes,optical properties,and cloud condensation nuclei(CCN)activity of particulate matter,which in turn has an important impact on atmospheric visibility,ground radiation forcing and hunman health.A Hygroscopic Tandem Differential Mobility Analyzer(H-TDMA)was deployed to measure the hygroscopic growth factors(GF)with chemical particulate composition monitor(MARGA)and related meteorological data during wintertime in urban region of Nanjing.The results were as follows:The mass concentration of sulphate,nitrate,and ammonium in haze period was(17.57±9.07)(26.16±11.39)(13.61±6.68)μg/m^(3) respectively,which was twice as much as(9.62±3.58)(12.12±7.51)(5.78±3.59)μg/m^(3) in non-haze period.The mas concenration of water-soluble chemical composition was NO^(-)_(3)>SO^(2-)_(4)>NH^(+)_(4)>Cl^(-)>K^(+)>Ca^(2+)>Na^(+)>Mg^(2+)in turn.Among then,NO^(-)_(3) had the largest contribution,accounting for 29%of PM_(2.5),followed by SO^(2-)_(4) with 14%,and NH^(+)_(4) with 8%.The other water-soluble components(Cl^(-),K^(+),Ca^(2+),Na^(+),Mg^(2+))accounted for 5.9%approximately.The mass concentration of SO^(2-)_(4),NO^(-)_(3) and NH^(+)_(4) had no obvious diurnal change and kept at a high level.The GF-PDF was bimodal during the observation.As the particle size increased,the hygroscopicity of more-hygroscopic particles increased,while the hygroscopicity of less-hygroscopic particles decreased.The peaks of less-hygroscopic particles were obvious than more-hygroscopic particles at 40nm.The GF of the more-hygroscopic and less-hygroscopic particles was 1.335±0.03,1.054±0.008 at 40 nm.The GF was 1.348±0.03,1.053±0.011 at 80nm.The GF of particles was 1.307±0.08,1.413±0.07 during the haze period,and was 1.230±0.03,1.300±0.03 during the non-haze period.There was no obvious change of the GF-PDF of less-hygroscopic particles in the cold air.The GF-PDF of more-hygroscopic particles was towards the left,the particles was cleared by the cold air,the mass concentration of old particles decreased,the hygroscopicity of particles decreased.The mass concentration of PM_(2.5) was(87.56±25.87)(69.31±28.75)μg/m^(3) during the haze and observation,the main secondary aerosol mass concentration accounted for 66%of PM_(2.5).The GF of particles decreased from 1.325±0.03 to 1.301±0.07.During the special period of the Spring Festival,the hygroscopicity of particles increased in less hygroscopic group and decreased in more hygroscopic group.The GF of more-hyroscopic particles at 110nm decreased obviously during the spring festival.The mass concentration of sulphate,nitrate,ammonium decreased obviously too,the change of hygroscopic growth factor was consistent with that of water-soluble chemical components.