Carrefour de l'innovation, Centre de recherche du centre hospitalier de l'université de Montréal, 850 St-Denis, Montréal, Québec H2X 0A9, Canada; School of Public Health, Université de Montréal, Montréal, Canada.
Carrefour de l'innovation, Centre de recherche du centre hospitalier de l'université de Montréal, 850 St-Denis, Montréal, Québec H2X 0A9, Canada; School of Public Health, Université de Montréal, Montréal, Canada.
Sci Total Environ. 2021 Jun 1;771:144652. doi: 10.1016/j.scitotenv.2020.144652. Epub 2021 Jan 18.
It has been hypothesized that ultrafine particles (UFP) in air pollution may cause lung cancer. In preparation for an epidemiologic case-control study to assess this hypothesis in Montreal, Canada, we conducted a UFP measurement campaign in order to create an exposure surface with which we could assign UFP exposure to subjects corresponding to their residential addresses. The purpose of this paper is to describe the temporal and spatial variability that underlies the creation of an exposure surface in the Montreal area, and to consider the implications for epidemiological exposure assessment. We identified 249 fixed sampling sites, selected to provide a dense spatial representation of the areas of residence of Montreal residents. We conducted a winter campaign and a summer campaign, and each of the sites was visited three times during each seasonal campaign. Each visit entailed a 20-minute measurement period for UFPs with a separate measurement each second. This provided data for temporal comparisons at each site between seasons, between visits and between seconds. The median of UFP measurements was 16,593 particles/cm in winter and 8919 particles/cm in summer. Across the 249 sampling sites the Spearman correlation coefficient between the UFP measurements of winter and summer was 0.35. Within each visit, correlation was below 0.50 between pairs of UFP measurements taken more than 60 s apart, and there was hardly any correlation among measurements taken more than 300 s apart. When sites were grouped by proximity to certain types of pollution sources, and the seven resulting groups compared, there were modest, albeit statistically significant, differences in UFP levels. There was moderate positive spatial autocorrelation in UFPs over the study area. High temporal variability of UFPs from short-term measurements campaigns will likely compromise the predictive validity of the exposure surface, and will eventually attenuate the epidemiologic risk estimates.
人们推测，空气污染中的超细颗粒（UFP）可能会导致肺癌。为了在加拿大蒙特利尔开展一项评估这一假设的流行病学病例对照研究，我们进行了一次 UFP 测量活动，以便创建一个暴露面，根据居民的住址为他们分配 UFP 暴露值。本文旨在描述创建蒙特利尔地区暴露面的时间和空间变异性，并考虑其对流行病学暴露评估的影响。我们确定了 249 个固定采样点，这些采样点的选择旨在为蒙特利尔居民居住区域提供密集的空间代表性。我们进行了冬季和夏季两个测量活动，每个季节的每个采样点都进行了三次访问。每次访问包括 20 分钟的 UFP 测量时间，每秒单独进行一次测量。这为每个季节、每个访问和每个秒数之间的时间比较提供了数据。冬季 UFP 测量的中位数为 16593 个/立方厘米，夏季为 8919 个/立方厘米。在 249 个采样点中，冬季和夏季 UFP 测量值之间的斯皮尔曼相关系数为 0.35。在每次访问中，两次测量时间间隔超过 60 秒时，相关性低于 0.50，而两次测量时间间隔超过 300 秒时几乎没有相关性。当根据接近某些类型污染源的位置对采样点进行分组，并对七个分组进行比较时，UFP 水平存在适度但具有统计学意义的差异。研究区域内 UFP 存在适度的正空间自相关。从短期测量活动中获得的 UFP 高度时间变异性可能会降低暴露面的预测有效性，并最终降低流行病学风险估计。
