京津冀地区冬半年空气污染天气分型研究

利用ERA-Interim再分析资料,采用PCT方法,对2013~2015年冬半年京津冀地区海平面气压场进行了客观分型;利用同期空气污染资料和常规气象观测资料,分析了不同天气类型下京津冀地区空气污染和气象要素特征,并选取典型重污染月份,分析了京津冀地区重污染天气过程特征及形成原因.结果表明,京津冀地区天气形势可分为9种类型,包括高压前部和高压南部等不易污染天气类型,以及高压场、高压后部、鞍型场和冷锋前部等污染天气类型;污染天气类型多表现为高湿小风,稳定能量大,最大混合层厚度低,不利于污染物扩散,各城市AQI均值多在150以上;2014年2月两次重污染过程均发生在连续多日维持高压场等污染天气型的情况下;污染过程期间高压系统演变引起北部偏北风增大,抑制了北部城市空气污染持续加重的趋势,而偏南风输送使得北部城市污染物浓度迅速升高.     

基于K-means聚类分析法的肇庆市干季PM2.5污染天气分型研究

通过分析肇庆市2013—2018年国控大气环境监测站的PM_(2.5)连续监测数据,发现肇庆市区PM_(2.5)浓度在干季(10月—次年4月)明显高于其余月份,轻度以上污染基本发生在干季,且PM_(2.5)浓度对年总浓度贡献达70.8%.基于Era-interim再分析资料采用K-means聚类分析法对2013—2018年干季逐日的海平面气压和10 m水平风进行分型,揭示了肇庆市易出现PM_(2.5)污染的6种大气环流形势,包括冷锋前部(CF)、变性高压脊(THR)、脊后槽前型(BRFT)、高压底后部(HSW)、弱冷高压脊(HR)和台风外围型(TP).2013—2016年易污染天气型影响天数呈明显减少趋势,2017—2018年呈增加趋势.不同天气型PM_(2.5)浓度与局地气象要素相关性不一致,其中CF、HR、HSW、TP天气型与湿度相关性最好,THR与风速、BRFT与气压相关性最好.PM_(2.5)污染除BRFT天气型主要以本地排放累积影响为主,其余易污染天气型存在不同尺度的外来输送影响,HSW、HR主要来自广州、清远、韶关, CF主要来自佛山、中山,THR来自广州、清远、佛山.同一污染天气型在不同月份的污染影响差异较大,其中HSW、THR污染型主要影响1月和10月,CF为1月和12月,HR为2月和12月,TP为10月,BRFT为1月和10—11月.不同年份的同一月份造成不同程度的PM_(2.5)污染除了排放影响,还与天气环流类型和同一天气型下的局地气象要素密切相关.     

上海秋冬季PM2.5污染天气形势的客观分型研究

通过分析2013—2015年上海地面PM_(2.5)质量浓度观测资料,发现11、12、1月3个月对PM_(2.5)年总浓度的贡献达到36.4%,对总污染日数的贡献达到50.4%,对PM_(2.5)环境质量的影响最显著.采用T-mode斜交旋转分解方法(PCT),对2012—2015每年11月、12月和次年1月的海平面气压场和10 m风场进行大样本客观分型研究,揭示了4种秋冬季上海PM_(2.5)易污染的天气环流类型,分别为冷锋(Cw)、高压后部弱气压场(WGh)、高压前部弱气压场(WGl和WGf).对上海而言,冷锋、高后弱气压、高前弱气压分别表现为有利于上游污染输送、本地静稳累积、以及本地积累和上游输送相叠加的天气学特征.对比2个典型污染月(2013年1月和12月)和清洁月(2014年11月和2015年11月)的逐日分型结果发现,Cw环流控制下污染输送对秋冬季上海PM_(2.5)环境质量影响显著,高前弱气压的维持是导致上海3次连续重度污染的重要原因.     

2016—2019年夏半年成都市区臭氧污染天气特征分析

为揭示成都市区臭氧污染气象条件特征,通过欧盟COST733天气客观分型软件对成都市区2016-2019年夏半年(5-9月)海平面气压场和500 hPa位势高度场进行大气环流形势分型,并结合同期臭氧监测数据、地面气象观测数据以及总云量实况分析产品,分析成都市区夏半年臭氧超标天气及气象要素特征.结果表明:成都市区2016-2019年夏半年共出现臭氧超标日数为159 d,超标率为26.0%,超标日主要集中于5-8月,小时超标多出现于14:00-17:00.臭氧污染日数最多的海平面气压场为弱低压型,其后依次为低压前部型、低压型、高压后部型.臭氧超标率最高的海平面气压场为低压前部型,其后依次为弱低压型、低压型、高压后部型.500 hPa位势高度场平直西风气流型臭氧超标日数最多,青藏高压型臭氧超标日数最少.青藏高压型是臭氧超标率最高的500 hPa位势高度场型,平直西风气流型臭氧超标率最低.成都市区臭氧超标日多出现在偏西北风下,近地面气象要素特征一般表现为风速1.2~1.6 m/s,气温在25℃以上,相对湿度多集中在70%左右,总云量和降水概率多低于60%,降水量级以小雨为主,太阳辐射和日照时数分别位于20.5~23.2 MJ/m2和6.0~7.8 h区间.小时臭氧超标近地面气象要素特征为气温和总辐射曝辐量相对较高,二者分别在30~36℃和0~3.5 MJ/m2之间,相对湿度在60%以下,总云量低于40%,以偏南风影响为主.研究显示,成都市区海平面气压场为低压型,500 hPa位势高度场为青藏高压型时,易发生臭氧污染.      

融合Lamb-Jenkinson分型法和LSTM神经网络的PM2.5预测研究

文章采用NCEP/NCAR逐日海平面气压场资料,利用Lamb-Jenkinson环流分型法对张家口大气环流进行分型,分析环流型与PM_(2.5)质量浓度之间的关系,并针对PM_(2.5)浓度的预测,提出一种融合Lamb-Jenkinson环流分型和LSTM神经网络混合模型的方法,即以环流指数为预测因子基于LSTM方法搭建PM_(2.5)质量浓度的预测模型。结果表明:影响张家口地区的主要环流型有反气旋型、气旋型、偏北平直型、西南平直型、偏西平直型、东北平直型等、西北平直型、偏东平直型。PM_(2.5)污染日出现的主要环流型为南气旋平直型、东南平直型、偏南平直型、偏东气旋型、西南气旋平直型、偏东平直型、气旋型等,而反气旋型和反气旋式平直环流型不利于污染出现。张家口地区的PM_(2.5)污染与地面环流有着密切的联系,当存在PM_(2.5)污染时,张家口地区处于日本海高压后部的均压场区域,污染越严重,日本海高压中心强度越强。模型预测结果的均方根误差为9.88、平均绝对误差为5.84、拟合优度达0.80,表明该模型具有一定的预报能力。     

基于PCT方法的京津冀冬季PM2.5重污染天气型分析

T模态斜交主成分分析法（PCT）分析的天气过程时间尺度越长,该算法的优势越明显,天气分型结果也更完整,可信度越高.利用京津冀地区2014年冬季-2019年冬季（每年12月-翌年2月）的环境监测资料,以区域平均PM_2.5日均值大于150 μg·m^-3为标准,筛选出72个京津冀地区PM_2.5重污染日,采用ERA5提供的0.25°×0.25°气象再分析资料,应用PCT算法将72个PM_2.5重污染日海平面气压场客观地分为高压前部型、锋前低压型、高压后部型、均压场型和弱低压型5种类型,分别占总PM_2.5重污染天数的34.72%、20.83%、16.67%、16.67%和11.11%.另外,对2017年2月12-16日京津冀地区PM_2.5重污染过程的分析表明,重污染天气过程中随着逐日天气型的演变,污染物浓度特征、近地面风场和大气污染物污染传输路径均发生相应变化.     

上海典型持续性PM2.5重度污染的数值模拟

本研究针对2013年1月23~24日的上海PM_(2.5)持续重污染过程,采用WRF-Chem大气化学模式以及PM_(2.5)质量浓度、能见度、气象要素等地面实测资料相结合的方式,揭示了造成上海冬季PM_(2.5)持续性重污染的一类"天气学必要成因",即一次弱冷空气活动过程导致了两种不利污染天气条件——"弱气压场(静稳形势)"和"弱冷空气扩散(输送形势)",两者先后影响上海造成PM_(2.5)浓度持续上升.主要过程如下:首先弱冷空气影响之前,上海处在不利的局地气象扩散条件下,受弱气压场控制10 h后本地PM_(2.5)质量浓度达到重度污染水平,之后夜间稳定边界层(地面静风和低层逆温)使得PM_(2.5)重度污染维持了7h,期间PM_(2.5)平均质量浓度为172.4μg·m~(-3).后期弱冷空气影响上海,虽然改善了局地扩散条件但是同时产生了明显的周边污染物输送,使得本地PM_(2.5)质量浓度升高并达到峰值(280μg·m~(-3)),继续加重污染水平,期间PM_(2.5)平均质量浓度为213.6μg·m~(-3).WRF-Chem模拟结果进一步表明,整个污染过程周边区域输送对上海PM_(2.5)平均贡献率为23%,其中两个阶段周边区域输送的平均贡献率分别为17.2%和32.2%,可见在不同的污染天气条件下周边污染源的贡献存在显著差异,因此可以根据对污染天气类型的预判制定应急减排方案.     

基于天气背景天津地区重污染天气特征分析

以天津地区长序列观测PM_(2.5)质量浓度资料为依托,基于天气背景对2014—2016年天津地区重污染天气特征进行分析,并以此为基础评估天津环境气象数值模式(WRF/Chem)在不同天气条件下的模拟效果.结果显示:2009—2016年天津地区重污染天气为341 d,约占全部天数的11.7%,重污染天气主要出现在每年的10月—次年3月,约占全年的82%,重污染天气出现的地面形势主要为锋前低压区、低压槽前、均压场和高压后,4类天气类型占所有重污染天气的73%.同一天气背景下,PM_(2.5)质量浓度模拟值与实况值之间的误差有相似之处,低压槽天气时细颗粒污染浓度模拟明显偏低;冷锋前低压区、华北地形槽和低压过程模拟值略有偏低;高压前和高压底天气模拟值略微偏高;数值模式天津地区重污染TS(Threat score)评分为0.68,漏报与低压槽辐合线模拟位置偏差、冷空气受污染反馈作用影响、小尺度闭合低压区未准确模拟3个因素密切相关;空报主要与冷空气过程影响时间模拟偏差、高压中心位置偏差及其输送通道建立时间影响密切相关.     

2015—2020年广东臭氧污染特征、污染天气分型及局地气象要素影响

利用2015—2020年广东省102个国控大气环境监测站臭氧(O₃)监测数据、广东省21个地市国家基本气象站地面气象观测数据和欧洲中期天气预报中心(ECMWF)第五代大气再分析全球气候数据(ERA5再分析资料)，研究了2015—2020年广东O₃污染特征、污染天气分型及局地气象要素影响.结果表明：2017—2019年广东O₃污染较严重，4—5月O₃浓度逐步上升，6月出现一定下降后7月开始持续上升，峰值出现在9—10月；珠三角O₃超标率明显高于全省其他地区，粤东O₃超标率低于全省平均水平，但浓度平均值高于全省其他地区.基于自组织映射(SOM)方法，将2015—2020年逐日海平面气压和10 m水平风进行分型得到12类环流型，按污染程度分为“污染天气型”、“轻污染天气型”和“清洁天气型”.其中“污染天气型”有台风外围叠加副高型、冷锋前部型、热带系统降水前静稳型、高压底前部型4类.12类天气型所对应的O₃浓度与日照时数、最高气温呈显著正相关...     

京津冀及周边区域PM2.5叠加沙尘重污染过程特征及预报效果分析

选取京津冀及周边区域2018年11月23日至12月4日一次大范围、长时间且PM_(2.5)叠加两次沙尘传输的复合型重度污染过程开展特征研究,分析了首要污染物PM_(2.5)和PM_(10)浓度的发展演变,以及污染气象影响因素;结合激光雷达地基和车载走航监测结果,以及HYSPLIT后向轨迹结果,讨论了区域污染传输的情况;并对重污染期间NAQPMS、CMAQ和CAMx这3个空气质量模式的预报效果进行了回顾分析.结果表明,研究时段PM_(2.5)叠加两次沙尘传输导致区域中南部多数城市达到重至严重污染水平,张家口、北京、石家庄、邯郸和郑州PM_(10)小时峰值分别为1 589、864、794、738和766μg·m~(-3),PM_(2.5)小时峰值浓度分别为239、319、387、321和380μg·m~(-3).地面弱气压场、高湿、逆温等静稳条件和沙尘是重要的污染气象和天气因素.激光雷达地基和车载走航监测数据结合HYSPLIT后向轨迹分析表明重污染期间区域西南和东南方向发生了PM_(2.5)传输;区域两次沙尘过程主要受西北路径传输影响.此外,NAQPMS、CMAQ和CAMx这3个模式均可较好地预测到京津冀及周边区域的重污染过程,但对个别城市预报略有偏差.该次重污染过程中模式对PM_(2.5)的预报效果要好于PM_(10),这与气象模式预报、大气化学反应机制、污染源清单的不确定性,以及重污染应急措施导致的污染源排放的改变有一定关系.     

Effects of two sludge application on fractionation and phytotoxicity of zinc and copper in the soil

The potential harm of heavy metals is a primary concern in application of sludge to the agricultural land. A pot experiment was conducted to evaluate the effect of two sludges on fractionation of Zn and Cu in soil and their phytotoxicity to pakchoi. The loamy soil was mixed with 0%, 20%, 40%, 60% and 80% (by weight) of digested sewage sludge (SS) and composted sludge (SC). The additions of both sludges caused a significant raise in all fractions, resulting in that exchangeable (EXCH) and organic bound (OM) became predominance of Zn and organic bound Cu occupied the largest portion. There was more available amount of Zn and Cu in SS treatments than SC treatments. During the pot experiment, the concentration of Zn in EXCH, carbonate (CAR) and OM and Cu in EXCH and OM fractions decreased in all treatments, so their bioavailability reduced. Germination rate and plant biomass decreased when the addition rate was high and the best yield appeared in 20% mixtures at the harvest of pakchoi. The two sludges increased tissue contents of Zn and Cu especially in the SS treatments. Zn in pakchoi was not only in relationship to ΔEXCH and ΔCAR forms but also in ΔOM forms in the sludge-soil mixtures. Tissue content of Cu in pakchoi grown on SC-soils could not be predicted by ΔEXCH. These correlation rates between Zn and Cu accumulation in pakchoi and variation of different fractions increased with time, which might indicate that sludges represented stronger impacts on the plant in long-term land application.     

Intraspecific differences in effects of co-contamination of cadmium and

A hydroponic experiment was carried out to study intraspecific differences in the effects of different concentrations of cadmium (Cd)(0-10 mg/L) and arsenate (As(V)) (0-8 mg/L) on the growth parameters and accumulation of Cd and As in six wheat varieties Jing-9428, Duokang-1, Jingdong-11, Jing-411, Jingdong-8 and Zhongmai-8. The endpoints of wheat seedlings, including seed germination,biomass, root length and shoot height, decreased with increasing the Cd and As concentrations. Significant differences in seed germination, biomass, root length, shoot height and the accumulation of Cd and As were observed between the treatments and among the varieties (p ＜ 0.05). The lethal dosage 50% were about 20, 80, 60, 60, 80 and 20 mg As/L for Jing-9428, Duokang-1, Jingdong-11,Jing-411, Jingdong-8 and Zhongmai-8, respectively, and the corresponding values for Cd were about 30, 80, 20, 40, 60 and 10 mg Cd/L, respectively. Among the six varieties, Duokang-1 was found to be the most resistant to Cd and As toxicity, and Zhongmai-8 was the most sensitive to Cd and As co-contamination. The resistance of the six varieties was found dependant on the seedling uptake of Cd and As. Duokang-1 was the most suitable for cultivation in Cd and As co-contaminated soils.     

Toxic effects of acetochlor, methamidophos and their combination on nifH gene in soil

Toxic effects of two agrochemicals on nifH gene in agricultural black soil were investigated using denaturing gradient gel electrophoresis （DGGE） and sequencing approaches in a microcosm experiment. Changes of soil nifH gene diversity and composition were examined following the application of acetochlor, methamidophos and their combination. Acetochlor reduced the nifH gene diversity （both in gene richness and diversity index values） and caused changes in the nifH gene composition. The effects of acetochlor on nifH gene were strengthened as the concentration of acetochlor increased. Cluster analysis of DGGE banding patterns showed that nifH gene composition which had been affected by low concentration of acetochlor （50 mg/kg） recovered firstly. Methamidophos reduced nifH gene richness that except at 4 weeks. The medium concentration of methamidophos （150 mg/kg） caused the most apparent changes in nifH gene diversity at the first week while the high concentration of methamidophos （250 mg/kg） produced prominent effects on nifH gene diversity in the following weeks. Cluster analysis showed that minimal changes of nifH gene composition were found at 1 week and maximal changes at 4 weeks. Toxic effects of acetochlor and methamidophos combination on nifH gene were also apparent. Different nifH genes （bands） responded differently to the impact of agrochemicals： four individual bands were eliminated by the application of the agrochemicals, five bands became predominant by the stimulation of the agrochemicals, and four bands showed strong resistance to the influence of the agrochemicals. Fifteen prominent bands were partially sequenced, yielding 15 different nifH sequences, which were used for phylogenetic reconstructions. All sequences were affiliated with the alpha- and beta-proteobacteria, showing higher similarity to eight different diazotrophic genera.     

Arsenic uptake by arbuscular mycorrhizal maize （Zea mays L.） grown in an arsenic-contaminated soil with added phosphorus

The effects of arbuscular mycorrhizal (AM) fungus (Glomus mosseae) and phosphorus (P) addition (100 mg/kg soil) on arsenic (As) uptake by maize plants (Zea mays L.) from an As-contaminated soil were examined in a glasshouse experiment.Non-mycorrhizal and zero-P addition controls were included.Plant biomass and concentrations and uptake of As,P,and other nutrients,AM colonization,root lengths,and hyphal length densities were determined.The results indicated that addition of P significantly inhibited root colonization and development of extraradical mycelium.Root length and dry weight both increased markedly with mycorrhizal colonization under the zero-P treatments,but shoot and root biomass of AM plants was depressed by P application.AM fungal inoculation decreased shoot As concentrations when no P was added,and shoot and root As concentrations of AM plants increased 2.6 and 1.4 times with P addition,respectively.Shoot and root uptake of P,Mn,Cu,and Zn increased,but shoot Fe uptake decreased by 44.6%,with inoculation, when P was added.P addition reduced shoot P,Fe,Mn,Cu,and Zn uptake of AM plants,but increased root Fe and Mn uptake of the nonmycorrhizal ones.AM colonization therefore appeared to enhance plant tolerance to As in low P soil,and have some potential for the phytostabilization of As-contaminated soil,however,P application may introduce additional environmental risk by increasing soil As mobility.     

Degradation of metabolites accumulated of benzo[a]pyrene by coupling Penicillium Chrysogenum with KMnO4

Several main metabolites of benzo[a]pyrene （BaP） formed by Penicillium chrysogenum, Benzo[a]pyrene-1,6-quinone （BP 1,6- quinone）, trans-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene （BP 7,8-diol）, 3-hydroxybenzo[a]pyrene （3-OHBP）, were identified by high-performance liquid chromatography （HPLC）. The three metabolites were liable to be accumulated and were hardly further metabolized because of their toxicity to microorganisms. However, their further degradation was essential for the complete degradation of BaP. To enhance their degradation, two methods, degradation by coupling Penicillium chrysogenum with KMnO4 and degradation only by Penicillium chrysogenum, were compared; Meanwhile, the parameters of degradation in the superior method were optimized. The results showed that （1） the method of coupling Penicillium chrysogenum with KMnO4 was better and was the first method to be used in the degradation of BaP and its metabolites; （2） the metabolite, BP 1,6-quinone was the most liable to be accumulated in pure cultures; （3） the effect of degradation was the best when the concentration of KMnO4 in the cultures was 0.01% （w/v）, concentration of the three compounds was 5 mg/L and pH was 6.2. Based on the experimental results, a novel concept with regard to the bioremediation of BaP-contaminated environment was discussed, considering the influence on environmental toxicity of the accumulated metabolites.     

Impact of atrazine and nitrogen fertilizers on the sorption of chlorotoluron in soil and model sorbents

Sorption of chlorotoluron in ammonium sulfate, urea and atrazine multi-solutes system was investigated by batch experiments. The results showed application of nitrogen fertilizers to the soil could affect the behavior of chlorotoluron. At the same concentration of N, sorption of chlorotoluron decreased as the concentration of atrazine increased on the day 0 and 6 in soil, respectively. The sorption of chlorotoluron increased from 0 to 6 d when soils were preincubated with deionized water, ammonium sulfate and urea solution for 6 d. That indicated incubation time was one of the most important factors for the sorption of chlorotoluron in nitrogen fertilizers treatments. The individual sorption isotherms of chlorotoluron in rubbery polymer and silica were strictly linear in single solute system, but there were competition sorption between pesticides or between pesticides and nitrogen fertilizers. That indicated the sorption taken place by concurrent solid-phase dissolution mechanism and sorption on the interface of water-organic matter or water-mineral matter.     

Distribution and ecological effect of mercury in Laogang landfill, Shanghai, China

Laogang landfill near Shanghai is the largest landfill in China, and receives about 10000 t of daily garbage per day, Samples of topsoil and plants were analyzed to evaluate mercury pollution from the landfill. For topsoil samples, there were significant correlations among total mercury （HgT）, combinative mercury （Hgc） and gaseous mercury （HgG）, and content of total organic carbon （TOC）, but, no significantly relationship was found between Hg content and filling time. Hg content changes in vertical profiles with time showed that the average Hgv of profiles 1992, 1996, and 2000 was similar, but their average HgG was quite different. HgT was significantly correlated with Hgc in profile 1992 and 2000, and Hgv was significantly correlated with Hg6 in profile 1996. HgG/Hgv ratio in profile samples decreased in the order of （HgG,/HgT）1992〉（HgG/HgT）1996〉〉（HgG/HgT）2000. A simple outline of Hg release in landfill could be drawn： with increasing of filling time, degradation undergoes different biodegradation, accordingly, gaseous mercury goes through small, more, and small proportion to total mercury. Distribution of Hg in plants was inhomogeneous, following the order of leaf〉root〉stem. The highest value of leaf may be associated with higher atmospheric Hg from landfill. Ligneous plants （e.g. Phyllostachys glanca, Prunus salicina and Ligustrum lucidum） are capable of enriching more Hg than herbaceous plants.     

EDTA-enhanced phytoremediation of lead contaminated soil by Bidens maximowicziana

Phytoremediation is a potential cleanup technology for the removal of heavy metals from contaminated soils.Bidens maximowicziana is a new Pb hyperaccumulator,which not only has remarkable tolerance to Pb but also extraordinary accumulation capacity for Pb.The maximum Pb concentration was 1509.3 mg/kg in roots and 2164.7 mg/kg in overground tissues.The Pb distribution order in the B. maximowicziana was:leaf>stem>root.The effect of amendments on phytoremediation was also studied.The mobility of soil Pb and the Pb concentrations in plants were both increased by EDTA application.Compared with CK(control check),EDTA application promoted translocation of Pb to overground parts of the plant.The Pb concentrations in overground parts of plants was increased from 24.23-680.56 mg/kg to 29.07-1905.57 mg/kg.This research demonstrated that B.maximowicziana appeared to be suitable for phytoremediation of Pb contaminated soil,especially,combination with EDTA.     

Potential of plant polyphenol oxidases in the decolorization and removal of textile and non-textile dyes

In this study an effort has been made to use plant polyphenol oxidases; potato （Solanum tuberosum） and brinjal （Solanum melongena）, for the treatment of various important dyes used in textile and other industries. The ammonium sulphate fractionated enzyme preparations were used to treat a number of dyes under various experimental conditions. Majority of the treated dyes were maximally decolorized at pH 3.0. Some of the dyes were quickly decolorized whereas others were marginally decolorized. The initial first hour was sufficient for the maximum decolorization of dyes. The rate of decolorization was quite slow on long treatment of dyes. Enhancement in the dye decolorization was noticed on increasing the concentration of enzymes. The complex mixtures of dyes were treated with both preparations of polyphenol oxidases in the buffers of varying pH values. Potato polyphenol oxidase was significantly more effective in decolorizing the dyes to higher extent as compared to the enzyme obtained from brinjal polyphenol oxidase. Decolorization of dyes and their mixtures, followed by the formation of an insoluble precipitate, which could be easily removed simply by centrifugation.     

Decomposition of alachlor by ozonation and its mechanism

Decomposition and corresponding mechanism of alachlor, an endocrine disruptor in water by ozonation were investigated. Results showed that alachlor could not be completely mineralized by ozone alone. Many intermediates and final products were formed during the process, including aromatic compounds, aliphatic carboxylic acids, and inorganic ions. In evoluting these products, some of them with weak polarity were qualitatively identified by GC-MS. The information of inorganic ions suggested that the dechlorination was the first and the fastest step in the ozonation of alachlor.