Single Particle Characterisation of the Aerosol in the Marine Boundary Layer and Free Troposphere over Tenerife, NE Atlantic, during ACE-2

In the framework of the 2nd Aerosol Characterization Experiment (ACE-2), in June and July 1997, size segregated samples were collected for single particle analysis on the island of Tenerife, in both the marine boundary layer (MBL) and the free troposphere (FT), to study the characteristics of the North Atlantic aerosol. A systematic assessment was made of the aerosol under background conditions and when the environment was perturbed by European emissions and/or Saharan dust. The aerosol particles were analysed by automated and manual SEM-EDX, followed by cluster analysis to identify the different particle types and their abundance. Basing on back trajectory calculations, particle numbers and volume concentrations, different periods can be identified regarding the origin of the sampled air masses. In the FT, the air masses were classified as clean Atlantic, Saharan dust from Africa or pollution from Europe. In the MBL, air masses were classified as clean, polluted or perturbed by emissions from Europe. For both the FT and MBL samples, the main changes in chemical composition were observed between the fine and coarse mode aerosol. The FT fine mode aerosol is dominated by S-poor aluminosilicates (62%) in the event of the dust samples or sulphates, carbonaceous particles (20%) and S-rich aluminosilicates (46%) in the polluted samples. For the larger fractions, a strong decreasing trend was observed for the sulphates (less than 20%) and carbonaceous particles (10%) in the polluted samples. The MBL fine mode was completely dominated by S-rich particles (polluted 55% and perturbed 59%), and to a lesser extent, carbonaceous and aged sea salt particles. In the coarse mode, the polluted air mass is dominated by sea salt particles (62%). Contrary to the fine fraction, the polluted air mass in the coarse fraction contained 5.3% of S-rich particles. The combined interpretation of the data from the analysis of size-fractioned particles and the calculated backward trajectories for air masses coming from Europe, Africa and the Atlantic, results in better insights on aerosol chemistry, especially for the comparison of the particle composition in the FT and the MBL.     

沙尘传输路径上气溶胶浓度与干沉降通量的粒径分布特征

利用2002年春季中国北京、青岛和日本福冈3个地区的分级气溶胶浓度资料,结合改进的Wil-liams模型,分析了沙尘传输路径上空气动力学直径≤11μm气溶胶(PM11)浓度和干沉降通量的粒径分布特征,并估算了黄海海域春季PM11的干沉降通量及不同粒径气溶胶的贡献。结果表明:3个地区PM11浓度粒径分布在非沙尘时期呈双峰分布,两个峰值分别出现在细颗粒(<2.1μm)部分和粗颗粒(2.1～11μm)部分;沙尘时期,3个地区PM11浓度粒径分布均趋于单峰分布,峰值位于粗颗粒部分,并且越靠近沙尘源地,这种趋势越明显。较强沙尘天气时期,粗颗粒部分的浓度峰值粒径从沙尘源地附近到黄海西岸、东岸呈降低趋势,但在一般沙尘天气时期,这种现象并不明显。沙尘时期和非沙尘时期,3个地区粗颗粒的干沉降通量均随粒径增加而增大,细颗粒的干沉降通量随粒径的变化不明显。虽然沙尘时期粗颗粒沉降通量较非沙尘时期有明显增加,但粗颗粒对PM11干沉降通量的贡献与非沙尘时期相比,并没有明显的变化。较强沙尘天气时期,3个地区粗颗粒的干沉降通量明显高于一般沙尘天气时期;细颗粒的干沉降通量较一般沙尘天气时期略有增加。黄海海域春季沙尘时期PM11的干沉降通量约为31.70～58.59mg.m-2.d-1,非沙尘时期约为8.33～15.94mg.m-2.d-1。粗颗粒是黄海海域春季PM11干沉降通量的主要贡献者,约占PM11干沉降通量的94.2%以上。     

2008年北京奥运会期间大气气溶胶物理特征分析

应用MODIS卫星的气溶胶产品资料和地面的光学粒子计数器的资料,对比分析了北京地区2006、2007、2008年7～9月的气溶胶光学厚度、细粒子光学厚度、Angstrom指数、气溶胶粒子数浓度谱及体积谱,发现2008年北京奥运会期间(7月20日～9月20日)的气溶胶光学厚度比2006、2007年同期明显降低,气溶胶细模态光学厚度占总光学厚度的比上升,Angstrom指数上升,气溶胶细粒子数浓度没有明显相对变化,而粗粒子数浓度则减少约50%.利用大气标高,将MODIS反演的气溶胶柱的质量浓度转化为地面气溶胶质量浓度.用粒子计数器得到的体积谱,在假定气溶胶粒子密度的情况下,计算出其质量浓度.将这两种方法得到的气溶胶质量浓度与国家环境保护部公布的空气质量指数换算得到的可吸入颗粒物(PM10)质量浓度进行比较.结果表明:北京奥运期间空气质量总体达到了国家二级空气质量标准;与2006、2007年同期相比,2008年气溶胶PM10质量浓度明显下降,而这主要是由气溶胶粗粒子的减少引起的.     

宁波一次罕见持续重度污染事件的成因分析

2013年12月1—10日宁波市出现历史罕见持续性重度污染事件。基于常规天气观测、浙江省自动气象站、宁波慈溪边界层风廓线雷达和凉帽山岛370 m高塔、宁波市和舟山市污染物监测等资料,应用美国NOAA HYSPLIT4模式进行粒子后向轨迹分析,并将CALMET诊断模式应用到WRF中尺度数值模式输出,对本次污染发展和消散过程宁波市3 km以下气象要素进行精细化诊断分析,计算通风系数。结果表明：（1）合适的环流背景是污染发展和持续的主要原因。气溶胶粒子浓度升高过程中有3次弱冷空气影响,主要表现在800 m以上层次,为粒子的输送提供了好的动力条件,却又不影响边界层风速和稳定性。弱冷空气间歇期风力弱,风向快速变化,利于粒子的循环滞留。（2）污染发展和持续阶段宁波市区3000 m以下持续弱下沉气流,夜间边界层高度低,200 m以下存在明显逆温层,导致气溶胶粒子在低层的堆积和能见度的降低。（3）污染发展和持续阶段夜间通风系数均小于1 m²/s,扩散条件很差,而污染消散阶段通风系数明显增大。没有外源性粒子输入时,通风系数与气溶胶粒子浓度成负相关。     

感应电机矢量控制系统的仿真研究

根据2008年4—7月黄山大气气溶胶观测资料,研究了气溶胶粒子的数浓度、谱分布特征及其与气象因子的关系,探讨了雾天和非雾天气溶胶颗粒物时间和尺度分布特点。分析发现,黄山光明顶春、夏季大气气溶胶数浓度的平均值分别为3.14×103个/cm3和1.80×103个/cm3,其中超细粒子（粒径小于0.1μm的粒子）在春夏季分别约占总粒子数浓度的79%和68%;高数浓度值集中在粒径0.04～0.12μm;积聚模态气溶胶粒子（0.1～1.0μm）在体积浓度分布和表面积分布中占很大比例。结合气象资料比较了雾天与非雾天气溶胶分布的差异,发现细粒子浓度非雾天大于雾天,而气溶胶数浓度与温度呈正相关,与相对湿度成反相关。结果还发现,黄山在春季以西北风和偏南风为主,西北风时气溶胶数浓度较高,在夏季主要以偏南风,特别是西南风为主,但是气溶胶数浓度的高值多发生在偏东风的条件下。     

Roadside, Urban, and Rural comparison of size distribution characteristics of PAHs and carbonaceous components of Beijing, China

Size-segregated aerosol samples were collected with a low-pressure impactor (LPI) at urban, roadside and rural sites in winter in Beijing. The size distribution of Polycyclic Aromatic Hydrocarbons (PAHs), organic carbon (OC) and elemental carbon (EC) were measured and this study focused on their size distributions and relationships of PAH to OC/EC. All PAHs show uni-modal at the accumulation mode (0.1–1.8 μm) and almost all PAHs are associated with fine particles. The absence of PAHs in the nucleus mode contributes to the coagulation under the condition of high concentration of the accumulation mode particles. The absence of PAHs in the coarse mode was probably attributed to the low temperature that restrained the redistribution of PAHs from the accumulation mode to the coarse mode. Flu(fluoranthene) and Pyr(pyrene, 4-ring) were the most abundant particulate PAHs ; however, IcdP(indeno[1,2,3-cd]pyrene) and BghiP(benzo[ghi]perylene, 6-ring) were rather low. Diagnostic ratios show vehicle and coal burning were the major sources of PAHs in winter. Ratios at rural site are obviously different from those found at roadside and urban sites. Lower value of OC/EC in the rural area than that in the urban area was probably resulted from coal burning prevailed in the rural area. OC1 and OC2 exhibit uni-mode distribution similar to their particle surface area distribution indicating their existence on particles by adsorption. OC3 and OC4 show bi-mode distribution. Grinding of biomass debris can be a probable source of OC3 and OC4 in the coarse mode. EC1 is mostly from the pyrolysis of OC; however, both the natural and anthropogenic emissions contribute to EC2. The correlation between size-segregated PAHs and carbonaceous component is also discussed to identify their sources.     

2004年北京秋季大气颗粒物的化学组分和来源特征

2004年9月在北京城区进行了大气颗粒物采样,样品用PIXE方法进行了分析,得到了20种元素的浓度及其谱分布。并对北京颗粒物的谱分布、富集因子和来源进行了分析研究。发现K元素浓度分布呈细粒态单峰谱分布,细粒态K富集因子较高,表明了生物质燃烧的主要贡献。因子分析结果还表明,土壤尘、生物质燃烧、煤烟尘、工业源和汽车尾气排放源对秋季北京局地排放源有明显贡献。     

Large aerosol particles in cirrus type clouds

Research flights in November 1990 over the central parts of the United States, Wyoming and Colorado, were aimed to the investigation of the properties and microstructure of cirrus clouds (mainly cirrocumulus lenticularis). Among the other parameters measured on board the NCAR Saberliner were the concentration and size distribution of submicron particles and, in some cases, the particle deliquescence. For coarse insoluble particles found inside and outside of cloud elements, size distributions and morphology information were obtained by evaluating inertial impactor samples with an optical microscope and scanning electron microscope. In addition, the coarse particle composition was determined by x-ray energy spectrum analysis. The following conclusions from these measurements are:The large and coarse particle size distribution can be roughly simulated by a log-normal function with the modus around r=0.5 μm. Particle concentrations are very variable between several tenths and several particles per cm³. Particle volume distribution features a distinct maximum around 0.75 μm without a broad plateau which was observed in the case of sampling at lower altitude. Aerosol composition heterogeneity at cirrus cloud level is well documented by the evaluation of the fine particle sampling taken with the UMR sampling system. This heterogeneity can be partly explained by the interaction between aerosol and cloud elements, which is documented by the measured particle size distribution curves inside and outside of cloud elements. Assuming that particle deliquescence is caused by H₂SO₄ and/or by (NH₄)₂SO₄, particle soluble mass fractions were found to be around 30% in the first case and about 40% in the second. The most frequently occurring elements in large and coarse particles at cirrus cloud level were Si, Cl, Ba, S, Ca and C.     

MEASUREMENTS OF PARTICLE NUMBER SIZE DISTRIBUTIONS AND NEW PARTICLE FORMATION EVENTS DURING WINTER IN THE PEARL RIVER DELTA REGION, CHINA

Particle number size distribution(PNSD) between 10 nm and 20 μm were measured in the Pearl River Delta(PRD) region in winter 2011.The average particle number concentration of the nucleation mode(10-20 nm),Aitken mode(20-100 nm),accumulation mode(100 nm-1μm) and coarse mode(1-20 μm) particles were 1 552,7 470,4 012,and 19 cm-3,respectively.The volume concentration of accumulation mode particles with peak at 300 nm accounted for over 70% of the total volume concentration.Diurnal variations and dependencies on meteorological parameters of PNSD were investigated.The diurnal variation of nucleation mode particles was mainly influenced by new particle formation events,while the diurnal variation of Aitken mode particles correlated to the traffic emission and the growth process of nucleation mode particles.When the PRD region was controlled by a cold high pressure,conditions of low relative humidity,high wind speed and strong radiation are favorable for the occurrence of new particle formation(NPF) events.The frequency of occurrence of NPF events was 21.3% during the whole measurement period.Parameters describing NPF events,including growth rate(GR) and source rate of condensable vapor(Q),were slightly larger than those in previous literature.This suggests that intense photochemical and biological activities may be the source of condensable vapor for particle growth,even during winter in the PRD.     

黑龙江省龙凤山区域大气本底站气溶胶光学特征分析

利用2010—2020年黑龙江省龙凤山区域大气本底站气溶胶光学特性长期观测资料, 分析并探讨了背景地区气溶胶光学厚度、波长指数、单次散射反照率、粒子体积谱分布以及气溶胶直接辐射强迫效应的变化特征。结果表明: 龙凤山区域气溶胶光学厚度最高值出现在7月, 平均值为0.67;最小值出现在12月、1月和2月, 平均值分别为0.17、0.02和0.18;气溶胶光学厚度在17时达到最高值为0.39。气溶胶波长指数在4—5月最低, 平均值分别为1.20和1.21;12月最高, 平均值为1.74;波长指数在12时达到峰值, 为1.44。单次散射反照率最低值分别出现在4月、8月和10月, 平均值分别为0.84、0.82和0.84;气溶胶单次散射反照率在12时出现峰值, 为0.95。龙凤山区域春季气溶胶粗粒子体积分数最高值出现在5月, 为0.04 μm³·μm^-2, 有效半径为3.85 μm; 夏季气溶胶细粒子体积分数最高值出现在7月, 为0.06 μm³·μm^-2, 有效半径为0.19 μm; 秋冬季龙凤山背景地区气溶胶细粒子和粗粒子体积分数均进一步减小。龙凤山区域地面和大气层顶气溶胶直接辐射强迫最高值均出现在7月, 分别为-94.44 W·m^-2和-22.33 W·m^-2。     

天空辐射计观测2006年春季北京地区气溶胶光学特性的研究

利用2006年3～5月天空辐射计观测数据反演得到北京地区春季大气气溶胶光学性质参数,包括大气气溶胶光学厚度(0.5μm)、Angstrm指数、单次散射反射比和粒子谱分布特征。结果表明:北京地区春季气溶胶平均光学厚度0.67,Angstrm指数0.54,单次散射比0.88,粒子吸收性质较弱,粒子谱呈双峰形,以粗粒子为主,粗、细模态粒子粒径分别集中在0.17μm和7.7μm左右。相比2004年此次观测期间气溶胶粒径较大,粒子体积浓度较高,散射作用在其消光特性中的比重略有下降。光学厚度日变化呈单峰型,日间单次散射比随时间逐渐递减,Angstrm指数在上午递减趋势明显,午后变得稳定。对同时观测的天空辐射计与CE-318不同波长光学厚度结果进行比较,结果显示两者得到的光学厚度相关性很好,各波长小时平均结果的相对误差小于7%。     

南京北郊冬季大气气溶胶及其湿清除特征研究

利用WPS(宽范围颗粒粒径谱仪)、雨滴潜仪和雾滴谱仪测量了2007～2008年冬季南京北郊大气气溶胶数浓度谱分布和降水强度,分析了气溶胶粒子的分布特征以及气溶胶粒径与湿清除系数的关系.结果表明:气溶胶粒子具有明显的双峰型R变化特征,数浓度主要集中在0.02～O.2μm粒径范围内,受汽车尾气排放、混合层高度变化以及颗粒物水平输送的影响较大.降雨、降雪和雾过程都对气溶胶粒子有不同程度的清除,降雨和浓雾对核模态和粗模态的气溶胶粒子的清除能力显著,降雪对粒径小于0.03μm的气溶胶粒子的清除能力较强.     

Aerosol Optical Properties and Radiative Impacts in the Pearl River Delta Region of China during the Dry Season

Aerosol optical properties and direct radiative effects on surface irradiance were examined using seven years(2006–2012)of Cimel sunphotometer data collected at Panyu—the main atmospheric composition monitoring station in the Pearl River Delta(PRD) region of China. During the dry season(October to February), mean values of the aerosol optical depth(AOD)at 550 nm, the ?ngstr?m exponent, and the single scattering albedo at 440 nm(SSA) were 0.54, 1.33 and 0.87, respectively.About 90% of aerosols were dominated by fine-mode strongly absorbing particles. The size distribution was bimodal, with fine-mode particles dominating. The fine mode showed a peak at a radius of 0.12 μm in February and October(~0.10μm~3μm~(-2)). The mean diurnal shortwave direct radiative forcing at the surface, inside the atmosphere(FATM), and at the top of the atmosphere, was-33.4 ± 7.0, 26.1 ± 5.6 and-7.3 ± 2.7 W m~(-2), respectively. The corresponding mean values of aerosol direct shortwave radiative forcing per AOD were-60.0 ± 7.8, 47.3 ± 8.3 and-12.8 ± 3.1 W m~(-2), respectively. Moreover,during the study period, FATMshowed a significant decreasing trend(p 0.01) and SSA increased from 0.87 in 2006 to 0.91 in 2012, suggesting a decreasing trend of absorbing particles being released into the atmosphere. Optical properties and radiative impacts of the absorbing particles can be used to improve the accuracy of inversion algorithms for satellite-based aerosol retrievals in the PRD region and to better constrain the climate effect of aerosols in climate models.     

Detection of Sahara dust intrusions during mixed advection patterns over south-east Italy: A case study

Measurements from July 4 to July 8, 2005 by a high resolution visible radiometer, a Raman lidar, a ground particulate matter sampler, and ground meteorological sensors have been combined in synergy to infer the intrusion over south-east Italy, of air masses from north-west Sahara, the Atlantic Ocean, and the continental Europe. It is shown that backscatter coefficient, depolarization-ratio, and lidar ratio vertical profiles represent the best tools to detect the intrusion of long range transported air masses and to monitor their effects on the vertical distribution of aerosol optical and microphysical properties. High resolution radiometers are instead important tools to monitor changes on columnar aerosol properties and size distributions.Backscatter coefficient, depolarization-ratio, and lidar ratio vertical profiles have revealed that aerosol optical and microphysical properties significantly changed with time and space during African dust outbreaks: the intrusion of dust particles that at first occurred above 2 km of altitude extending up to 6 km, affected the all aerosol load down to ground within few hours. Aerosol size distributions showed during dust events a clear bimodality with an accumulation mode maximum at 0.24 µm and a coarse mode maximum at 0.94 μm. Conversely, we have found that during the advection of air masses from the Atlantic and continental Europe, aerosol particles were mainly located below 2 km, their optical and microphysical properties were affected by smaller changes in time and space, and were characterized by depolarization ratios rather close to those due to a pure molecular atmosphere. In this case bimodal size distributions with an accumulation mode showing two sub-modes at 0.16 μm and 0.24 μm, respectively and a coarse mode centred at 0.94 μm have also been observed.     

Influence of meteorological variability upon aerosol mass size distribution

Aerosol mass size distribution has been measured by using an optical particle counter. The measurements were done in an urban background location in the western Mediterranean during winter 2006. The study has been focused in determining the mass size distribution under special meteorological conditions like moderate rain, considerable winds and high atmospheric stability. The results obtained showed a mass predominance of accumulation mode during rain and high stability periods although for different reasons. In the case of rain, it is due to greater atmospheric cleansing effectiveness that rain has upon coarse mode particles. However, during stagnant periods, the meteorological situation favored coagulation processes among nucleation mode particles giving like result a mass increase in the accumulation mode. Finally, strong winds favor the resuspension of the largest particles and the dispersion of particles with sizes inferior to 7.5 μm. Similar results have been reproduced using principal component analysis (PCA). In this way, three components were identified. The first (PC1) represents particles in the accumulation mode. The second component (PC2) is constituted by coarse particles to 7.5 μm, and the third (PC3) corresponds to coarser particles. The contribution of each group to the overall average concentration was determined: 27.2% corresponds to particles with sizes belonging within the first component, 35.4% to PC2 and 37.3% to PC3. Important percentage variability for each component under meteorological episodes has been obtained. Results obtained showed an important increase of PC1 during Rainy Days (53.8%) and High Pollution Days (40.2%). Contrary to this on Windy Days this component decreases to 7.4%. However, during this kind of day PC3 increases to 64.6%.     

Biomass Burning in Southern Africa: Individual Particle Characterization of Atmospheric Aerosols and Savanna Fire Samples

Ambient atmospheric aerosols and savanna fireparticulate emission samples from southern Africa werecharacterised in terms of particle classes and theirnumber abundance by electron probe X-ray microanalysis(EPXMA). About ten particle classes were identifiedfor each sample. The major classes werealuminosilicates and sea salts for ambient coarse(2–10 m equivalent aerodynamic diameter (EAD))samples, and K-S and S-only particles for ambient fine(<2 m EAD) samples. The K-S particles are oneof the major products of biomass burning. The EPXMAresults were found to be consistent with the resultsfrom bulk analyses on a sample by sample basis. Forsavanna fire fine samples, quantitative EPXMA revealedthat many particles had a composition of simple saltssuch as KCl. Some particles had a deviatingcomposition in the sense that more ionic species wereinvolved in sustaining the balance between cations andanions, and they were composite or mixed salts.Because of extensive processing during the atmospherictransport, the composition of the K-S particles in theambient samples was different from K₂SO₄,and such particles were enriched with S. The finepyrogenic KCl particles and the fine sea-saltparticles were much depleted in chlorine.     

中国地区边界层大气气溶胶辐射吸收特性

采用粒子采样法对中国２３个地区边界层气溶胶的吸收系数作了测量,研究了其分布特征。结果表明：中国地区边界层气溶胶的吸收系数在１０＾－６－１０＾－３ｍ＾－１之间,明显呈北高南低的趋势,四川盆地和贵州有一相对较高的中心,吸收系数与粒子含量之间的相关系数为０．７４,吸收系数与粒子含量的分布一致性较好。小颗粒的吸收性能好于大颗粒。     

2007和2008年夏季北京奥运馆大气PM10与PM2.5质量浓度变化特征

为了监测北京奥运主场馆附近大气颗粒物的污染状况以及评估奥运污染源减排措施对北京大气颗粒物质量浓度变化的影响,利用颗粒物在线监测仪器TEOM于2007年和2008年夏季,在奥运主场馆附近的中国科学院遥感应用研究所办公楼楼顶对大气颗粒物PM10和PM2.5进行了连续同步观测。结果表明,2007年夏季监测点附近大气PM10与PM2.5质量浓度的平均值分别为153.9和71.2μg.m-3,而2008年夏季PM10与PM2.5质量浓度的平均值分别为85.2和52.8μg.m-3。与奥运前一年同时段相比,奥运时段大气PM10和PM2.5的质量浓度分别下降44.5%和25.1%。对比分析奥运前后的2次典型污染过程发现,空气相对湿度的增加和偏南气流输送的共同影响易造成大气颗粒物的累积增长,而降雨的湿清除作用和偏北气流则会使大气颗粒物浓度迅速降低。在相近的气象条件下,奥运前后的污染过程中,大气细粒子的日均增长速率分别为25.1和13.9μg.m-3.d-1,而大气粗粒子的日均增长速率分别为20.8和2.2μg.m-3.d-1,奥运时段污染累积过程中大气粗、细粒子的增长速率分别显著低于和略低于奥运前同时段污染过程中颗粒物的增长速率。污染源减排措施的实施是奥运期间大气颗粒物质量浓度降低的主要原因,从控制效果来看,奥运期间实施的污染源减排措施对大气粗粒子的控制效果明显好于大气细粒子。     

Traffic aerosols (18 nm particle size 18 μm) source apportionment during the winter period

In November 2004–January 2005, a micro orifice uniform deposit impactor (MOUDI) and a Nanometer (nanometer)-MOUDI were used in the center of Taiwan to measure particle size (18 nm particle size 18 μm) distributions of atmospheric aerosols at a traffic site during the winter period. The average Mass in Media Aerodynamic Diameter (MMAD) of suspended particles is 0.99 μm this study. As for the ultra fine and nanometer (nanometer) particle mode, the composition order for these major ions species was SO₄²⁻ NH₄⁺ NO₃⁻ Mg²⁺ Ca²⁺ Na⁺ K⁺ Cl⁻. An ion Chromatography (DIONEX-100) was used to analyze major anion species, Cl⁻, NO₃⁻, SO₄²⁻ and cation species, NH₄⁺Na⁺, K⁺, Ca²⁺Mg²⁺. Their concentrations were also extracted from various particles size modes (nanometer (nanometer), ultra fine, fine and coarse). The results obtained in this study also indicated that the average portions for the major ionic species (SO₄²⁻, NH₄⁺ and Mg²⁺) in the nanometer (nanometer), ultra fine, fine and coarse particulate modes are about 34%, 37%, 63% and 30%, respectively at this traffic sampling site during the winter period.     

Aerosol spectra and new particle formation observed in various seasons in Nanjing

The aerosol number spectrum and gas pollutants were measured and the new particle formation （NPF） events were discussed in Nanjing. The results showed that the size distributions of aerosol number concen- trations exhibited distinct seasonal variations, implying the relations of particle sizes and their sources and sinks. The number concentrations of particles in the nuclei mode （10-30 nm）, Aitken mode （30-100 nm）, accumulation mode （100 -1000 nm） and coarse mode （〉1μm） varied in the order of summer 〉 spring 〉 autumn, summer 〉 autumn 〉 spring, autumn 〉 summer 〉 spring, and spring 〉 autumn 〉summer, re- spectively. The diurnal variation of total aerosol number concentrations showed three peaks in all observed periods, which corresponded to two rush hours and the photochemistry period at noon. In general, the NPF in summer occurred under the conditions of east winds and dominant air masses originating from marine areas with high relative humidity （50%-70%） and strong solar radiations （400 -700 W m-2）. In spring, the NPF were generally accompanied by low relative humidity （14%-30%） and strong solar radiations （400-600 W m-2）. The new particle growth rates （GR） were higher in the summertime in the range of 10- 16 nm h-1. In spring, the GR were 6.8-8.3 nm h-1. Under polluted air conditions, NPF events were seldom captured in autumn in Nanjing. During NPF periods, positive correlations between 10- 30 nm particles and 03 were detected, particularly in spring, indicating that NPF can be attributed to photochemical reactions.