Carslaw David C, Ropkins Karl, Bell Margaret C
Institute for Transport Studies, University of Leeds, Leeds LS2 9JT, UK.
Environ Sci Technol. 2006 Nov 15;40(22):6912-8. doi: 10.1021/es060543u.
An 8-year (1998-2005), hourly data set of measurements of NOx, NO2, PM10, PM2.5, and PMcoarse (defined as PM(2.5-10)) from a busy roadside location in central London has been analyzed to identify important change-points in the time series using a cumulative sum (CUSUM) technique. Randomization methods were used to estimate the uncertainty level associated with the change-points with uncertainty intervals derived using a bootstrap approach. The results show that there is a clear change-point increase for NO2 coinciding with the introduction of the London congestion-charging in February 2003 (95% confidence interval from January-March 2003). At this time there was both an increase in bus numbers and buses fitted with catalyzed diesel particulate filters, which increase direct emissions of NO2. A highly statistically significant change-point was also observed for PMcoarse (95% confidence interval from December 2002-February 2003), which also occurred close to the time of the congestion charge introduction and is most closely related to the increase in bus flows. The increase in PMcoarse at this time has largely compensated for reductions in the concentration of PM2.5, such that the concentration of PM10 has remained almost constant. Comparing the 2 years before and after the introduction of congestion charging, the increment in NO2 above background increased from 22 to 34 ppb and PMcoarse increased from 4 to 9 microg m(-3). These results could have important implications for meeting European air quality standards that currently set limits for PMlo rather than PM2.5.
对伦敦市中心一个繁忙路边位置的8年（1998 - 2005年）每小时氮氧化物、二氧化氮、可吸入颗粒物（PM10）、细颗粒物（PM2.5）和粗颗粒物（定义为PM(2.5 - 10)）测量数据集进行了分析，以使用累积和（CUSUM）技术识别时间序列中的重要变化点。采用随机化方法估计与变化点相关的不确定性水平，并使用自助法得出不确定性区间。结果表明，二氧化氮有一个明显的变化点增加，与2003年2月伦敦拥堵收费的引入时间一致（95%置信区间为2003年1月至3月）。此时，公交车数量增加，且配备了催化柴油颗粒过滤器的公交车也增加，这增加了二氧化氮的直接排放量。粗颗粒物也观察到一个具有高度统计学显著性的变化点（95%置信区间为2002年12月至2003年2月），该变化点也发生在拥堵收费引入时间附近，并且与公交流量增加关系最为密切。此时粗颗粒物的增加在很大程度上抵消了细颗粒物浓度的降低，使得可吸入颗粒物浓度几乎保持不变。比较拥堵收费引入前后的两年，二氧化氮高于背景值的增量从22 ppb增加到34 ppb，粗颗粒物从4微克/立方米增加到9微克/立方米。这些结果可能对满足目前针对可吸入颗粒物而非细颗粒物设定限值的欧洲空气质量标准具有重要意义。
