不同NOx条件下有机胺光氧化二次气溶胶的形成及其云凝结核活性

本研究采用烟雾箱模拟的方法,在不同NO_x条件下,对二甲胺、三甲胺、二乙胺、苯胺、乙醇胺与OH自由基光氧化生成二次气溶胶(SA)的过程及其云凝结核(CCN)活性进行了测定.结果表明,当不添加NO_x时,乙醇胺的SA生成系数(FAC)最高(0.22),而三甲胺与苯胺的FAC较低(≤0.05),二甲胺与二乙胺的FAC则趋于0,且该条件下生成的气溶胶CCN活性较弱,三甲胺、苯胺与乙醇胺生成的SA吸湿性参数(κ_SA)值为0.10～0.22,符合典型有机物κ值.当添加NO_x后,各有机胺生成的SA粒径、密度变大,且SA的生成系数均有提高,在高NO_x浓度条件下按SA的生成系数对有机胺排序：乙醇胺>苯胺>二甲胺>三甲胺>二乙胺;同时添加NO_x后SA的CCN活性变强,在高NO_x浓度条件下按其CCN活性对有机胺排序：乙醇胺>二甲胺>苯胺>二乙胺>三甲胺,其中,乙醇胺最高(κ_SA=0.65)...     

羟基自由基浓度对二次有机气溶胶形成的影响

在烟雾腔中光照甲苯/亚硝酸甲酯(CH3ONO)/NO混合物,模拟了羟基自由基(OH·)启动甲苯光氧化反应生成二次有机气溶胶的过程.结果表明,二次有机气溶胶的生成数量随着CH3ONO的浓度增加而增加;在CH3ONO浓度为225.4μL/L时,二次有机气溶胶的生成数量达到最大;此后,增加CH3ONO的浓度反而会降低二次有机气溶胶的粒子密度.因此,对于二次有机气溶胶的形成过程来说,存在一个羟基自由基浓度的最佳值.     

硫酸铵气溶胶对甲苯-NOx-空气体系光化学反应的影响

利用大气模拟烟雾箱,研究了硫酸铵气溶胶对甲苯-NO_x-空气体系光化学反应的影响.结果表明,硫酸铵作为气溶胶种子,其存在可以加快反应过程中颗粒物（particle matter, PM）的生成速度,并提高甲苯的气溶胶产率.在高浓度的硫酸铵气溶胶种子条件下,其初始浓度对反应过程中NO_x、NO和O₃的浓度变化没有明显的影响,但对二次有机气溶胶（secondary organic aerosol, SOA）的生成有显著影响.在硫酸铵气溶胶种子浓度小于160 μg·m^-3时,SOA的产率随初始气溶胶种子浓度的增大而增大,从最小7.2％到最大11.7％,其增幅超过60％.     

郑州市PM2.5中有机酸的污染特征、来源解析及二次生成

大气颗粒物中的有机酸广泛参与大气中的各种物理化学反应,对二次有机气溶胶和霾的形成贡献极大,因此分析颗粒物中有机酸的浓度分布特征、评估其污染来源、探究其二次生成,对深入研究有机气溶胶及其二次转化具有重要意义.在郑州市不同季节采集大气细颗粒物（PM_2.5）样品,识别并定量二元酸类、脂肪酸类和树脂酸类有机酸共30种,探究其浓度分布特征、季节变化、来源贡献及二次生成.定量的二元酸类以丙二酸（di-C₃）和琥珀酸（di-C₄）含量最为丰富,并且表现出明显的季节变化特征：夏季 > 秋季 > 冬季 > 春季;脂肪酸类表现出明显的双峰优势,以棕榈酸和硬脂酸（C₁₈）最为丰富,季节变化特征为冬季最高,春季最低.利用主成分分析结合多元线性回归（MLR）方法对郑州市PM_2.5中的有机酸进行来源解析,结果表明,35%的有机酸来自于燃烧源和交通源,24%来自于烹饪源、23%来自于二次生成以及17%来自于天然源.利用标记物种的比值（如di-C₃ /di-C₄、F/M和C_18：1 /C₁₈）探究有机气溶胶二次形成及其老化过程.结果表明,夏季光化学反应剧烈,有机气溶胶老化或二次生产比例较高,冬季光化学反应较弱,有机气溶胶老化程度较低.采用相关性分析与MLR相结合的方法,量化了气相氧化和液相氧化对二元酸形成的相对贡献,气相氧化在采样过程中起主导作用,占比为58%,特别是夏季,占总二次转化的61%.     

酸性硫酸铵种子气溶胶对甲苯二次有机气溶胶形成和组分的影响研究

酸性硫酸铵是中国城市大气中常见的亚微米气溶胶颗粒,它在二次有机气溶胶（SOA）的形成中起着至关重要的作用.本文利用自制的烟雾腔系统开展了酸性硫酸铵种子气溶胶对甲苯SOA形成和化学组分的影响研究,采用PM_2.5粒子检测仪、高效液相色谱质谱仪和紫外-可见分光光度计测量反应产生的SOA粒子的浓度和组分.实验结果表明,酸性硫酸铵种子气溶胶能够显著促进甲苯SOA的形成.相比于没有种子气溶胶存在时,甲苯SOA中检测到的羧酸组分,甲苯光氧化产生的二醛化合物在酸性硫酸铵颗粒表面上发生非均相反应产生的咪唑类化合物是酸性硫酸铵种子气溶胶存在时甲苯SOA的主要组分.气相二醛化合物能在高浓度酸性硫酸铵种子气溶胶表面快速发生非均相酸催化反应产生咪唑类产物.这为研究高浓度酸性无机细粒子背景下,大气咪唑类含氮有机物棕色碳的形成机制研究提供了实验依据.     

硫酸铵气溶胶对甲苯-NOx-空气体系光化学反应的影响

利用大气模拟烟雾箱,研究了硫酸铵气溶胶对甲苯-NOx-空气体系光化学反应的影响.结果表明,硫酸铵作为气溶胶种子,其存在可以加快反应过程中颗粒物(particle matter,PM)的生成速度,并提高甲苯的气溶胶产率.在高浓度的硫酸铵气溶胶种子条件下,其初始浓度对反应过程中NOx、NO和O3的浓度变化没有明显的影响,但对二次有机气溶胶(secondary organic aemsol,SOA)的生成有显著影响.在硫酸铵气溶胶种子浓度小于160 μg·m-3时,SOA的产率随初始气溶胶种子浓度的增大而增大,从最小7.2%到最大11.7%,其增幅超过60%.     

南京地区相对湿度对气溶胶含量的影响

为了研究南京地区相对湿度对气溶胶的影响,利用位于南京信息工程大学的拉曼-瑞利-米氏激光雷达,分析湿度廓线对消光系数的影响;利用2014年3月~2015年2月国控点环境监测数据对可吸入颗粒物浓度特征进行统计,并与相对湿度进行逐月和四季对比分析,并计算各参数之间的相关系数,以期为南京市的城市布局与规划、大气污染治理等提供更多参考.结果表明,低空气溶胶的消光系数廓线与相对湿度廓线变化趋势高度一致,地面相对湿度与可吸入颗粒物浓度在一定湿度范围（以不发生重力沉降为界限）内,相对湿度越大越有利于颗粒物的形成,超过这个范围,相对湿度越大,颗粒物浓度越低,在南京地区,对于PM₁₀来说,这个界限在40%~49%,对于PM_2.5来说,这个界限在50%~59%.     

大气气溶胶有效折射率的计算及相对湿度对它的影响

为了了解气溶胶折射率对研究大气气溶胶的辐射效应的影响,给出了一种基于气溶胶散射和吸收特性的有效媒介近似方法,以计算大气气溶胶的有效折射率。用此方法计算所得北京冬季气溶胶的有效折射率为１．５６１－０．０５７ｉ,其与实测值相比是比较一致的。     

氨对甲苯二次有机气溶胶形成和化学组分的影响研究

氨(NH_3)是大气中常见的主要碱性污染气体,能够影响二次有机气溶胶(SOA)的形成和化学组分.本文利用自制的烟雾腔系统开展了NH_3对甲苯SOA形成和化学组分的影响研究,先后采用扫描移动粒径谱仪(SMPS)、气溶胶激光飞行时间质谱仪(ALTOFMS)、紫外-可见分光光度计(UV-Vis)、衰减全反射傅里叶变换红外光谱仪(ATR-FTIR)和荧光光谱仪(MF)测量反应产生的SOA粒子的物理化学性质.结果显示,在光照60 min的时间范围内,有NH_3条件下形成的SOA质量浓度和中心粒径相比于无NH_3条件下分别增加了50%和25%,这说明NH_3能够显著促进甲苯SOA的形成.与无NH_3条件下相比,NH_3存在时甲苯SOA化学组分的紫外可见吸收光谱在270 nm处有明显的吸收峰;红外吸收光谱出现了CN、C—N、N—H键的吸收峰;激光解吸附质谱图中含有m/z=67(C_3H_3N_2~+)、m/z=41(C_2H_2N~+)和m/z=28(CH2N+)碎片峰.这些谱图信息综合表明是NH_3和甲苯SOA中的二醛组分反应形成了咪唑类新产物.这为研究人为源SOA的形成机制提供了实验依据.     

成都市冬季相对湿度对颗粒物浓度和大气能见度的影响

利用成都市城区2015年12月的连续在线观测数据,如相对湿度（RH）、能见度、颗粒物（PM₁₀、PM_2.5和PM₁）浓度、气态污染物（SO₂和NO₂）浓度以及PM_2.5中SO₄^2-和NO₃^-浓度,探讨RH对颗粒物浓度和大气能见度的影响.结果表明,高颗粒物浓度和高RH协同作用导致低能见度事件.观测阶段,PM_2.5在PM₁₀中的平均比重为64%,表明成都市冬季细颗粒物污染严重;随着RH增加,PM_2.5/PM₁₀显著增加,表明高RH会加重细颗粒物污染.随着PM_2.5浓度增加,能见度呈幂指数下降;在相同PM_2.5浓度下,RH越高,能见度越低.当颗粒物浓度较低时,RH对能见度的影响作用较强;当颗粒物浓度较高时,大气消光主要由PM_2.5浓度控制,RH对能见度的影响减弱.当RH大于70%时,硫氧化率（SOR）和氮氧化率（NOR）的均值分别从0.27和0.11（RH小于40%）增长至0.40和0.19,表明较高RH对二次硫酸盐和硝酸盐的生成有显著的促进作用,二次硫酸盐和硝酸盐单独或协同影响空气质量.     

Influence of environmental temperature and relative humidity on photocatalytic oxidation of toluene on activated carbon fibers coated TiO2

TiO₂ supported on active carbon fiber (TiO₂/ACF), an absorbable photocatalyst, is a new kind of material applied in air purification. In this paper, the influence of environmental temperature (T) and relative humidity (RH) on the gas-solid adsorption of toluene and the photocatalytic oxidation (PCO) efficiency of adsorbed toluene on TiO₂/ACF were studied, and then, the purification capability of TiO₂/ACF was estimated. PCO results showed that although the PCO efficiency increased under high RH and T levels, the amount of adsorption of toluene decreased. Moreover, quantitative analysis results of intermediates indicated that more environmental risk emerged when PCO of toluene was carried out at higher environmental T and RH levels because more toxic intermediates would be accumulated on the TiO₂/ACF. So, it is significant to control the environmental T and RH conditions in the application of the PCO technique. T = 25°C and RH530% is the optimal condition for purifying toluene in our experimental system. __________ Translated from Urban Environment & Urban Ecology, 2007, 20(5): 10–13 [译自: 城市环境与城市生态]     

Characterization of products from photooxidation of toluene

Photooxidation reaction of toluene in smog chamber systems was initiated by the UV radiation of tolucne/CH5ONO/NOx mixtures. The products of the photooxidation reaction of toluene and its subsequent reactions were analyzed directly utilizing Fourier transform infrared spectrometer （FTIR）. Detailed assignments to FTIR spectrum of gas-phase products were given. The information of some important functional groups in the products, such as, carbonyl groups （C-O）, hydroxyl groups （-OH）, carboxylic acid （- COOH）, C-C bonding, N O bonding and C-H bonding （C H）, was got from this analysis. These results were compared to those analyzed by aerosol time of flight mass spectrometer （ATOFMS）. It was found that there are some differcnccs between FTIR analysis of gas-phase products and that of particle-phase, for example, the products with carbonyl groups, which were connected to unsaturated chemical bonds, was relatively higher in the gas phase, while kctoncs, aldehydes, carboxylic acid and organonitrates were the dominant functional groups in the aerosol-phase reaction products. The possible reaction pathways of some important products in the gas phase were also discussed.     

天津冬季相对湿度对气溶胶浓度谱分布和大气能见度的影响

于2013年1月连续在线观测天津城区气溶胶数浓度谱分布和大气能见度,并结合相关气象资料,探讨相对湿度(RH)对气溶胶浓度谱分布和大气能见度的影响.结果表明,观测期间发生了4次连续雾霾天气过程, 4次雾霾天气过程对应着气溶胶粒子数浓度的连续高值,低能见度天气系高浓度气溶胶粒子和高相对湿度协同所致;随着RH增大,PN1和PN2.5-10呈增长趋势, RH>90%后,PN1和PN2.5-10有所降低,PN1-2.5则持续增长,高RH对气粒转化和气溶胶粒子的碰并聚合作用明显;气溶胶吸湿增长因子计算表明,高RH下水汽对能见度影响很大,尤其是大雾天气下其影响甚至可能超过气溶胶粒子浓度对其的影响.     

Size distribution of the secondary organic aerosol particles from the photooxidation of toluene

In a smog chamber, the photooxidation of toluene was initiated by hydroxyl radical （OH.） under different experimental conditions. The size distribution of secondary organic aerosol（SOA） particles from the above reaction was measured using aerodynamic particle sizer spectrometer. It was found from our experimental results that the number of SOA particles increased with increasing the concentration of toluene. As the reaction time prolonged, the sum of SOA particles was also increased. After a reaction time of 130 min, the concentration of secondary organic aerosol particles would be kept constant at 2300 particles/cm^3. Increasing illumination power of blacklamps could significantly induce a higher concentration of secondary organic aerosol particle. The density of SOA particles would also be increased with increasing concentration of CH30NO, however, it would be decreased as soon as the concentration of CH30NO was larger than 225.2 ppm. Nitrogen oxide with initial concentration higher than 30. 1 ppm was also found to have little effect on the formation of secondary organic aerosol.     

Size distribution and chemical composition of secondary organic aerosol formed from Cl-initiated oxidation of toluene

Secondary organic aerosol (SOA) formed from Cl-initiated oxidation of toluene was investigated in a home-made smog chamber. The size distribution and chemical composition of SOA particles were measured using aerodynamic particle sizer spectrometer and the aerosol laser time-of-flight mass spectrometer (ALTOFMS), respectively. According to a large number of single aerosol diameter and mass spectra, the size distribution and chemical composition of SOA were obtained statistically. Experimental results showed that SOA particles created by Cl-initiated oxidation of toluene is predominantly in the form of fine particles, which have diameters less than 2.5 m (i.e., PM2.5), and glyoxal, benzaldehyde, benzyl alcohol, benzoquinone, benzoic acid, benzyl hydroperoxide and benzyl methyl nitrate are the major products components in the SOA. The possible reaction mechanisms leading to these products are also proposed.     

Observations of nitrous acid and its relative humidity dependence in Shanghai

Nitrous acid, HNO2, is an important precursor of OH radicals in the troposphere. Measurements of HNO2 and NO2, using differential optical absorption spectroscopy （DOAS）, were performed in Shanghai, China for a period from October 22, 2004 to January 4, 2005. The mean （and median） hourly concentrations of HNO2 and NO2 during this period were 1.1 （0.7） ppb and 24 （21.4） ppb respectively. A correlation between HNO2/NO2 and PM10 mass concentrations was obtained. This correlation suggests that significant heterogeneous chemical production of HNO2 may occur through NO2 reactions on aerosol surfaces. This hypothesis was further supported by detailed analysis of selected pollution episodes in this study. At the same time, the water dependence of HNO2 formation was studied by analysis of relative humidity （RH）. It showed that the maximum HNO2/NO2 ratio was increased along with RH below 70% and inhibited at RH〉70%.