紫外光降解黑索金(RDX)的研究

本课题对模拟废水中RDX在紫外光和氧化剂等作用下的光化学降解情况进行了研究.运用正交设计法来安排实验,获得了废水的酸碱度、过氧化氢与亚铁离子的投加量、紫外光照射的时间等RDX降解的最佳条件.自行设计了光化学降解装置.在最佳条件下对RDX模拟废水进行光化学处理,并利用721分光光度计以及TOC-500测试仪对实验结果进行鉴定,取得了较为满意的结果.     

北京地区对流层低层臭氧及硫酸盐气溶胶的时空分布

基于OMI/Aura卫星资料,分析了北京地区2007~2016年近10a对流层O₃浓度（0~3km）、硫酸盐气溶胶光学厚度（0~2km）、SO₂（边界层以内）柱浓度时空演变特征.结果表明,近10a来北京地区O₃浓度总体呈现上升趋势,最低值在2007年,浓度为33.65 μg/m³;硫酸盐气溶胶污染总体变化呈现先下降后增长的趋势,2007年硫酸盐气溶胶污染最为严重,2011年污染最轻,对应的AOD值为0.252,但在2014年以后,硫酸盐气溶胶污染又出现增长趋势;SO₂浓度在2007~2016年总体呈现下降的变化趋势,且下降趋势明显,最高值为2007年,最低值出现在2016年,最低值比最高值降低了60.42%,但在2011年污染出现反弹.北京O₃季节变化明显,夏季高、春秋次之、冬季低;硫酸盐气溶胶污染季节特征与O₃相同;SO₂污染主要集中在冬季,采暖期污染程度高于非采暖期.     

水体系中十二烷基苯磺酸钠的光化学氧化动力学研究

系统研究了在天然日光和高压汞灯照射下十二烷基苯磺酸钠(SDBS)在蒸馏水、人工海水和天然海水中的光降解情况。结果发现,SDBS的光化学氧化的速率会受到溶液介质、光源、重金属离子、光敏剂以及pH的影响。SDBS的光化学氧化反应符合一级动力学规律,其一级反应速率常数为0.0184 min-1~0.0281 min-1。SDBS在蒸馏水中的光降解速率大于在人工海水和天然海水中的光降解速率,其主要原因是蒸馏水中溶解更多的氧。天然海水中重金属离子Zn2+和Cd2+能加快SDBS的光氧化速率,光敏剂的加入也会加快SDBS的光氧化速率。此外,酸性条件下有利于SDBS的光降解。     

Photochemical degradation of nonylphenol in aqueous solution：The impact of pH and hydroxyl radical promoters

The degradation of nonylphenol (NP) in aqueous solution with UV, H₂O₂/UV, and Fenton/photo-Fenton processes was studied. The efficacy of direct and hydrogen peroxide photolysis proved to be dependent on the pH value. The addition of H₂O₂ to UV treatment improved NP degradation. The application of UV photolysis and the H₂O₂/UV system at pH 7 resulted in low pseudo first-order rate constants at 10^-4 sec^-1. In the experiments at elevated pH values the pseudo-first order rate constants increased to 10^-3 sec^-1. The efficacy of the Fenton process was lower in comparison with UV and hydrogen peroxide photolysis. The addition of UV irradiation to the H₂O₂/Fe²⁺ system substantially improved NP degradation efficacy. In terms of performance, the photo-Fenton process was similar to the H₂O₂/UV process. The most favourable process for complete nonylphenol degradation considering both operational cost and treatment efficacy was H₂O₂/UV at pH 11 and 250 mol/L H₂O₂.     

Characteristics of ozone and ozone precursors (VOCs and NOx) around a petroleum refinery in Beijing, China

A field measurement campaign for ozone and ozone precursors(VOCs and NOx) was conducted in summer 2011 around a petroleum refinery in the Beijing rural region. Three observation sites were arranged, one at southwest of the refinery as the background, and two at northeast of the refinery as the downwind receptors. Monitoring data revealed the presence of serious surface O3 pollution with the characteristics of high average daily mean and maximum concentrations(64.0 and 145.4 ppbV in no-rain days, respectively) and multi-peak diurnal variation. For NOx, the average hourly concentrations of NO2 and NO were in the range of 20.5–46.1 and 1.8–6.4 ppbV, respectively. For VOC measurement, a total of 51 compounds were detected. Normally, TVOCs at the background site was only dozens of ppbC, while TVOCs at the downwind sites reached several hundreds of ppbC. By subtracting the VOC concentrations at background, chemical profiles of VOC emission from the refinery were obtained, mainly including alkanes(60.0% ± 4.3%), alkenes(21.1% ± 5.5%) and aromatics(18.9% ± 3.9%). Moreover, some differences in chemical profiles for the same measurement hours were observed between the downwind sites; the volume ratios of alkanes with low reactivity and those of alkenes with high reactivity respectively showed an increasing trend and a decreasing trend. Finally, based on temporal and spatial variations of VOC mixing ratios, their photochemical degradations and dispersion degradations were estimated to be 0.15–0.27 and 0.42–0.62, respectively, by the photochemical age calculation method, indicating stronger photochemical reactions around the refinery.     

天气型对北京地区近地面臭氧的影响

臭氧(O3)是夏秋季北京城市大气光化学污染物中的首要气态污染物,气象因素是影响其浓度水平和变化规律的主要因子之一.2008年7月~2008年9月,在北京市4个站点进行了臭氧、氮氧化物(NOx)和一氧化碳(CO)浓度的同步连续观测,并对同期天气型进行了分类比对分析.结果显示,观测期间,北京地区处于低压前部(主要是蒙古气旋)和高压前部的比例分别为42%和20%,分别是造成臭氧浓度高值和低值的主要背景场.处于低压前部控制时,高温、低湿以及局地环流形成的山谷风造成区域臭氧累积,小时最大值(体积分数)高达102.2×10-9,并随气压的升高以3.4×10-9Pa-1的速率降低,山谷风风向的转变决定了臭氧浓度最大值出现时间,峰值出现在14:00左右;处于高压前部控制时,低温、高湿以及系统性北风造成区域臭氧低值,小时最大值(体积分数)仅为49.3×10-9,系统性北风将臭氧峰值出现时刻推后到16:00左右.北京地区臭氧光化学污染呈现出区域一致性,并与天气型有较好相关,关注天气型结构和演变对预报大气光化学污染具有重要意义.     

湿地植被叶面积指数对光化学指数和光能利用率关系的影响————基于实测数据和PROSPECT-SAIL模型

光化学指数PRI(Photochemical Reflectance Index)是估算光能利用率LUE(Light Use Efficiency)的一种快速监测的有效指标,分析各种因素对二者的影响是提高估算精度的前提.论文针对三种杭州湾典型湿地植物 [旱柳(Salix matsudana),柽柳(Tamarix chinensis)和芦苇(Phragm itescommunis)],实地观测了其光合作用及日变化,叶面积指数以及同步植被光谱.同时采用PROSPECT-SAIL模型模拟叶面积指数LAI(Leaf Area Index)从小到大变化时植被冠层反射率,分析LAI的变化对冠层PRI的影响.结果表明:1)三种植被在日变化上,芦苇,旱柳和柽柳的PRI和LUE的相关性较好,R²分别为0.581 6,0.524 6和0.514 6;而对同一种植被在不考虑时间变化的条件下,PRI和LUE的相关性会有所减弱,对于LAI较小的冠层,PRI不能精确反映LUE;2)当LAI < 5时,冠层下土壤背景对冠层PRI影响较大,在不同土壤背景下,土壤亮度低的对冠层PRI影响较小;3)当LAI > 5时,土壤背景对冠层PRI影响较小,冠层自身的LAI才是影响PRI和LUE相关性的决定因素.因此,PRI和LUE关系模型还需要进一步探索和完善,引入更精确的模型和参数,不断提高LUE估算的准确度.     

Wintertime peroxyacetyl nitrate (PAN) in the megacity Beijing: Role of photochemical and meteorological processes

Previous measurements of peroxyacetyl nitrate(PAN) in Asian megacities were scarce and mainly conducted for relative short periods in summer. Here, we present and analyze the measurements of PAN, O3, NOx, etc., made at an urban site(CMA) in Beijing from 25 January to 22 March 2010. The hourly concentration of PAN averaged 0.70 × 10 9mol/mol(0.23 × 10 9–3.51 × 10 9mol/mol) and was well correlated with that of NO2but not O3, indicating that the variations of the winter concentrations of PAN and O3in urban Beijing are decoupled with each other. Wind conditions and transport of air masses exert very significant impacts on O3, PAN, and other species. Air masses arriving at the site originated either from the boundary layer over the highly polluted N-S-W sector or from the free troposphere over the W-N sector. The descending free-tropospheric air was rich in O3, with an average PAN/O3ratio smaller than 0.031, while the boundary layer air over the polluted sector contained higher levels of PAN and primary pollutants, with an average PAN/O3ratio of 0.11. These facts related with transport conditions can well explain the observed PAN-O3decoupling. Photochemical production is important to PAN in the winter over Beijing. The concentration of the peroxyacetyl(PA) radical was estimated to be in the range of 0.0014 × 10 12–0.0042 × 10 12 mol/mol. The contributions of the formation reaction and thermal decomposition to PAN's variation were calculated and found to be significant even in the colder period in air over Beijing, with the production exceeding the decomposition.     

北京城市大气中NOx、CO、O3的变化规律研究

对北京市大气中Ｏ３浓度变化规律及Ｏ３浓度变化与ＮＯｃ、ＣＯ浓度变化之间的关系进行了研究。结果表明：Ｏ３浓度随温度指数上升,Ｏ３浓度和ＮＯｘ、ＣＯ浓度变化之间无简单规律可寻。