奥运前期与奥运期间北京市大气细颗粒物特征比较分析

利用城市生态系统研究站对北京市奥运前后(2008年6～9月)大气中细颗粒物(PM2.5)进行连续监测,获得不同阶段PM2.5日平均浓度的动态特征,分析气象因素、人为控制管理措施对颗粒物浓度的影响.结果表明,近北五环的生态中心站点(RCEES)颗粒物日均浓度平均值为0.067 mg.m-3,奥运期间的颗粒物浓度(0.060 mg.m-3)比奥运前期(0.081 mg.m-3)减少了约26%.而位于南二环市中心的教学植物园站点(JX)颗粒物浓度平均含量为0.078 mg.m-3.JX站点奥运期间的颗粒物浓度(0.069 mg.m-3)比奥运前期(0.095 mg.m-3)减少了约27%.各个阶段PM2.5的日变化都基本呈现双峰态势.第一个峰值出现在08:00～10:00左右,RCEES站点颗粒物浓度为0.068 mg.m-3,JX站点浓度值为0.089 mg.m-3;另一个峰值出现在晚20:00～22:00左右,RCEES和JX站点颗粒物浓度为0.079 mg.m-3和0.083 mg.m-3,这主要与上班交通高峰导致的尾气排放污染和道路扬尘污染等有关.研究气象参数发现奥运期间与奥运前期气象条件无显著差异,属于高温高湿风力不大的典型北京夏季天气条件.奥运期间颗粒物浓度与温度呈显著正相关(P<0.01),而与风速、相对湿度及降水相关性不显著(P>0.05).而连续多年大气污染综合治理措施和奥运空气质量保障措施的实施,产生了显著环境效益.在自然因素相差不大的条件下,人为控制因素对奥运期间颗粒物的下降起到主导作用.     

上海市秋季蔬菜硝酸盐含量及风险摄入评估

对上海市秋季蔬菜中硝酸盐的含量及居民硝酸盐摄入情况做分析和评估,于2009年9～11月从上海市松江、奉贤、金山和浦东4个区的采集了大棚和露地的25个品种439个蔬菜样品,用紫外分光光度法测定蔬菜的硝酸盐含量.结果表明,所有蔬菜样品中,污染程度严重的占41.46%,中、重度污染的占30.53%,轻度的占28.02%.不同种类蔬菜的硝酸盐含量从高到低依次为叶菜类、根茎类、瓜类、豆类、茄果类,同类蔬菜不同品种的硝酸盐含量差别也较大.浦东新区叶类、根茎类蔬菜硝酸盐含量大棚明显高于露地,奉贤区和松江区蔬菜硝酸盐含量均值都为露地高于大棚.上海市居民每日通过蔬菜摄入的硝酸盐为445.22 mg,比WHO/FAO的ADI值高出38.42%,研究结果表明需要加强蔬菜施肥的监督管理.     

Estimation of daily intake of potentially toxic elements from urban street dust and the role of oral bioaccessibility testing

The pseudo-total and oral bioaccessible concentration of six potentially toxic elements (PTEs) in urban street dust was investigated. Typical pseudo-total concentrations across the sampling sites ranged from 4.4 to 8.6 mg kg⁻¹ for As, 0.2-3.6 mg kg⁻¹ for Cd, 25-217 mg kg⁻¹ for Cu, 14-46 mg kg⁻¹ for Ni, 70-4261 mg kg⁻¹ for Pb, and, 111-652 mg kg⁻¹ for Zn. This data compared favourably with other urban street dust samples collected and analysed in a variety of cities globally; the exception was the high level of Pb determined in a specific sample in this study. The oral bioaccessibility of PTEs in street dust is also assessed using in vitro gastrointestinal extraction (Unified Bioaccessibility Method, UBM). Based on a worst case scenario the oral bioaccessibility data estimated that Cd and Zn had the highest % bioaccessible fractions (median >45%) while the other PTEs i.e. As, Cu, Ni and Pb had lower % bioaccessible fractions (median <35%). The pseudo-total and bioaccessible concentrations of PTEs in the samples has been compared to estimated tolerable daily intake values based on unintentional soil/dust consumption. Cadmium, Cu and Ni are well within the oral tolerable daily intake rates. With respect to As and Pb, only the latter exceeds the TDI_oral if we model ingestion rate based on atmospheric ‘dustiness’ rather than the US EPA (2008) unintentional soil/dust consumption rate of 100 mg d⁻¹. We consider it unlikely that even a child with pica tendencies would ingest as much as 100 mg soil/dust during a daily visit to the city centre, and in particular to the sites with elevated Pb concentrations observed in this study.     

准好氧填埋场作业台阶表面CH_4气体的释放通量研究

采用静态通量箱/气相色谱法对河北某准好氧填埋场不同填埋龄作业台阶表面CH4气体的释放通量进行了测定。结果表明,准好氧填埋场作业台阶表面CH4气体的释放通量存在较大差异,其最大值和最小值分别为215.51和0.13g/(m2.d)。各填埋作业区中越靠近导气管的区域CH4气体释放量越大,而相同填埋作业区上午、中午和下午释放的CH4气体通量差异相对较小,但呈下午>中午>上午的趋势。填埋龄为8,12,16和20个月的各填埋作业区中CH4气体的平均释放通量分别为4.79,21.15,81.04和7.44g/(m2.d),并随着填埋龄的增加呈先增加后降低的趋势,在填埋16个月左右达到其释放高峰。此外,准好氧填埋场不同填埋龄作业区表面的CH4气体释放通量随着距离导气管距离的增加呈指数函数递减。