Abstract Ozone is a serious health concern and the only major pollutant in Ontario that is increasing, despite major efforts to control atmospheric pollutants in North America. Ambient ozone levels are affected by local atmospheric conditions (temperature, humidity, radiation, precipitation) and the concentration of its main precursors, nitrogen oxides (NOx) and volatile organic compounds (VOCs). In the present study, our aim is to elucidate the day-to-day and seasonal variability of the influence of synoptic atmospheric descriptors on daily average ozone concentrations, as well as to establish a predictive framework of the likelihood of exceedance of harmful levels in Southern Ontario. Using 31 stations in Southern Ontario with daily ozone concentration data from 2007 to 2015, we developed parsimonious models using as predictors a suite of atmospheric variables, available from the National Centers for Environmental Prediction and the National Center for Atmospheric Research (NCEP/NCAR) reanalysis dataset, and terms that recreate the seasonality and weekend/weekday effects of the previous day ozone concentrations. In all sites, seasonal (among-month) variability was distinctly lower than within-month variability. Our analysis showed that the population size reduced the average ambient ozone concentrations, increased their variability, and decreased the predictive power of our models. Ambient ozone levels in higher latitude sites displayed stronger dependence on the antecedent conditions, whereas the human activities weakened the serial correlation in the ozone time series in urban areas. Seasonal changes in the magnitude and sign of the slopes of the atmospheric predictors were consistent within the spatial domain of our study: shortwave radiation consistently increased ambient ozone levels, temperature displayed a positive relationship during the summer but a negative one during the winter; humidity was characterized by a negative relationship with ozone; precipitation increased ozone during late summer and winter, with no consistent effect during the rest of the year; wind speed and direction also showed contrasting effects between summer and winter months. Seasonality strongly affected the probability of exceedance in low population sites but had a minor role in more densely populated areas, while the difference in ozone concentrations between weekend and weekdays increased in urban sites. Overall, our results suggest that population and seasonality of the prevailing ambient conditions affect the local daily average ozone concentrations by modulating the importance of different processes and can thus be used to understand why high ozone concentrations may occur locally even during winter months.

中文翻译：

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加拿大安大略省南部臭氧浓度的季节性模式和纬度和人口的独特特征

摘要 臭氧是一个严重的健康问题，并且是安大略省唯一一个不断增加的主要污染物，尽管北美为控制大气污染物做出了重大努力。环境臭氧水平受当地大气条件（温度、湿度、辐射、降水）及其主要前体、氮氧化物 (NOx) 和挥发性有机化合物 (VOC) 的浓度影响。在本研究中，我们的目标是阐明天气大气描述符对每日平均臭氧浓度影响的日常和季节性变化，并建立一个预测框架，预测南方地区超过有害水平的可能性。安大略。使用安大略省南部 31 个站点的 2007 年至 2015 年每日臭氧浓度数据，我们使用一系列大气变量作为预测器开发了简约模型，这些变量可从国家环境预测中心和国家大气研究中心 (NCEP/NCAR) 再分析数据集获得，以及重现季节性和周末/工作日影响的术语之前的日臭氧浓度。在所有站点中，季节性（月间）变异性明显低于月内变异性。我们的分析表明，人口规模降低了平均环境臭氧浓度，增加了它们的可变性，并降低了我们模型的预测能力。高纬度地区的环境臭氧水平对前因条件的依赖性更强，而人类活动削弱了城市地区臭氧时间序列的序列相关性。在我们研究的空间范围内，大气预测因子的幅度和符号的季节性变化是一致的：短波辐射持续增加环境臭氧水平，温度在夏季呈正相关，而在冬季呈负相关；湿度的特点是与臭氧呈负相关；降水在夏末和冬季增加了臭氧，但在一年中的其余时间没有持续的影响；风速和风向也显示出夏季和冬季月份的对比效果。季节性强烈影响人口稀少地区的超标概率，但在人口稠密地区影响较小，而城市地区周末和工作日之间的臭氧浓度差异增加。全面的，