Holmes Jason, Hassini Sonia
Department of Civil Engineering, McMaster University, Hamilton, ON L8S 4L7 Canada.
Water Air Soil Pollut. 2021;232(4):158. doi: 10.1007/s11270-021-05096-1. Epub 2021 Apr 15.
The Air Quality Health Index (AQHI) is an aggregate indicator of air pollution used to communicate to Canadians the health impact of short-term exposure to current air pollutant levels. Understanding the stochastic behaviour of the AQHI can aid public health officials in predicting air pollution levels, determining the likelihood and duration of air quality advisories, and planning for increased strain on the health care system during periods of higher air pollution. Previous research has applied discrete-time Markov chains to investigate stochastic behaviour of air pollution indices but only in a handful of regions and none with the same climatic characteristics as Canadian regions. In this study, we investigated the stochastic behaviour of AQHI risk categories in Ontario (34 air monitoring stations) for 5 years from 2015 to 2019. We employed discrete-time Markov chains using three of the AQHI risk categories (Low Risk, Moderate Risk, High Risk) as states to determine (1) the transition probabilities between these states, (2) the long-run proportion of time spent in each state, and (3) the mean persistence time of each state. These results were then used to assess spatial trends in the stochastic behaviour of AQHI risk categories and the likelihood and duration of air quality advisories. Overall, the air quality (as characterised by the AQHI) in Ontario tends to decrease as population density increases. Urban areas spent a greater proportion of time in higher risk categories, and tended to remain in the higher risk categories for longer before transitioning.
空气质量健康指数（AQHI）是一种空气污染综合指标，用于向加拿大人传达短期暴露于当前空气污染物水平对健康的影响。了解AQHI的随机行为有助于公共卫生官员预测空气污染水平、确定空气质量警报的可能性和持续时间，以及规划在空气污染较高时期医疗系统面临的压力增加的应对措施。以往的研究已应用离散时间马尔可夫链来研究空气污染指数的随机行为，但仅在少数地区进行，且没有与加拿大地区具有相同气候特征的研究。在本研究中，我们调查了2015年至2019年安大略省（34个空气监测站）5年间AQHI风险类别的随机行为。我们使用离散时间马尔可夫链，将AQHI的三个风险类别（低风险、中度风险、高风险）作为状态，以确定（1）这些状态之间的转移概率，（2）在每个状态中花费的长期时间比例，以及（3）每个状态的平均持续时间。然后，这些结果被用于评估AQHI风险类别随机行为的空间趋势以及空气质量警报的可能性和持续时间。总体而言，安大略省的空气质量（以AQHI为特征）往往随着人口密度的增加而下降。城市地区在较高风险类别中花费的时间比例更大，并且在转变之前往往会在较高风险类别中停留更长时间。
