垃圾焚烧厂周边大气二噁英含量及变化特征——以北京某城市生活垃圾焚烧发电厂为例

2013年4月至2014年1月对北京市某生活垃圾焚烧厂周边4km范围内5个采样点环境空气中二噁英含量、组成特征及季节变化特征进行了分析.结果表明该垃圾焚烧厂周边环境空气中PCDD/Fs质量浓度的变化范围为8.3~115pg/m³,毒性当量(TEQ)变化范围为0.11~1.9pg I-TEQ/m³,其中秋季1个采样点和冬季全部采样点超出日本环境空气质量标准限值(0.6pg I-TEQ/m³).1,2,3,4,6,7,8-HpCDF和OCDF均是四季空气中PCDD/Fs质量浓度的主要贡献单体,而2,3,4,7,8-PeCDF是总TEQ贡献最大的单体.空间分布特征表现为近源点位(~400m)浓度水平较高而其他点位(>1000m)浓度水平与距污染源距离远近没有显著相关性;季节变化特征表现为冬季值显著高于其他季节,分析可能与冬季采暖及大气扩散条件差导致的大气整体污染较重有关.样品中二噁英同族体及异构体分布指纹谱图与焚烧设施排放烟气存在差别,主成分分析(PCA)源解析结论与指纹谱图特征分析结论一致,体现为多种污染源共同作用的影响.二噁英呼吸暴露剂量估算结果表明该区域人群呼吸暴露风险总体处于较为安全的水平(0.034~0.161pg I-TEQ/(kg·d)),但仍需关注大气重污染天气发生时的呼吸暴露风险.

Concentrations,spatial and seasonal variations of PCDD/Fs in ambient air around a municipal solid waste incinerator-a case study in Beijing

The concentrations, profiles and seasonal variations of PCDD/Fs in ambient air around a municipal solid waste incinerator(MSWI) in Beijing from April 2013 to January 2014 were investigated. The mass concentrations and TEQ of 2, 3, 7, 8-substituted PCDD/Fs in the air samples ranged from 8.3 to 115pg/m³ and from 0.11to 1.9pg I-TEQ/m³, respectively. The concentration values at 1sampling site in autumn and all 5sampling sites in winter were higher than the ambient air standard of 0.6pg I-TEQ/m³ for dioxins regulated in Japan. 1, 2, 3, 4, 6, 7, 8-HpCDF and OCDF dominated PCDD/Fs in all the samples for all four seasons, while 2, 3, 4, 7, 8-PeCDF was the dominant congener contributing to TEQ. The spatial distribution basically exhibited a trend that the concentrations at site close to the MSWI(~400m) are higher whereas those at other sites(>1000m) are comparable and not related to the distances from the source. Seasonal variation showed obviously higher concentration in winter than the other three seasons, which may attribute to domestic heating and worse atmospheric dispersion that occur in winter. The homologue and congener profiles of PCDD/Fs in the air samples differed from those of the flue gas emission from the MSWI, consistent with the principal component analysis results, indicating that the concentrations of PCDD/Fs in ambient air were not affected by the MSWI exclusively, but jointly influenced by multiple sources. Dioxin inhalation exposure dose estimation showed that the dioxin inhalation exposure risk of residents living in the studied area was at a relative safe level(0.034~0.161pg I-TEQ/(kg·d)). However, the dioxin inhalation exposure risk in heavily polluted seasons still needed great concerns.