Abstract Nitrogen oxides (NO and NO2, collectively NOX) derived from vehicle exhausts are critical pollutants with significant implications for urban air quality and human and environmental health. In this study, we investigate trends in measured ambient nitrogen dioxide (NO2) and NOx mixing ratios at urban traffic - dominated monitoring sites in the UK for the period 2009–2016. We apply an oxidant analysis approach alongside a number of assumptions to the ambient data to determine trends in the inferred primary NO2/NOx ratio, and examine evidence for enhanced vehicle “cold start” effects upon these inferred emissions. Ambient NO2 and NOX mixing ratios have experienced an overall decrease of 17.2% and 11.3% respectively for the locations considered over this time period. The inferred primary NO2/NOx ratio for the majority of the study locations is found to have fallen by 29% (from 0.175 to 0.125) as a monthly mean from 2009 to 2016, with a statistically significant median decrease of 0.32 percentage points per year. However, during cold weather (temperatures less than or equal to 5 OC), the inferred primary NO2/NOx ratio averaged across all locations, when compared with normal conditions (temperatures higher than 5 OC) increased from 0.062 (±0.004) to 0.102 (±0.001) (64.5% higher) and from 0.056 (±0.004) to 0.098 (±0.001) (75% higher) for cold morning and evening rush hours, with substantially greater increases at some sites. This “cold start” result suggests that the combination of recent vehicle driving history and ambient weather conditions, in conjunction with technological constraints on the operating temperature range of emission control systems in some vehicles, affects NOx emissions and hence has a detrimental impact upon air quality in urban environments. Increased cold start emissions imply an increased NO2 - derived health burden from air pollution, under certain meteorological conditions, assessment of which should consider changes in vehicle use as a result of weather, and hence altered personal exposure.

中文翻译：

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英国环境监测数据中车辆冷启动主要二氧化氮排放及其对城市空气质量的影响调查

摘要 汽车尾气中的氮氧化物（NO 和 NO2，统称为 NOX）是重要的污染物，对城市空气质量以及人类和环境健康具有重大影响。在这项研究中，我们调查了 2009 年至 2016 年期间英国城市交通主导监测点测量的环境二氧化氮 (NO2) 和 NOx 混合比的趋势。我们将氧化剂分析方法与环境数据的一些假设一起应用，以确定推断的主要 NO2/NOx 比率的趋势，并检查证据表明车辆“冷启动”对这些推断排放的影响增强。在这段时间内，所考虑的地点的环境二氧化氮和氮氧化物混合比分别下降了 17.2% 和 11.3%。从 2009 年到 2016 年，大多数研究地点的推断初级 NO2/NOx 比值下降了 29%（从 0.175 到 0.125），从 2009 年到 2016 年，平均下降了 0.32 个百分点，具有统计学意义。然而，在寒冷天气（温度小于或等于 5 OC）期间，与正常条件（温度高于 5 OC）相比，所有地点的推断初级 NO2/NOx 比值从 0.062（±0.004）增加到 0.102（ ±0.001) (高出 64.5%) 和从 0.056 (±0.004) 到 0.098 (±0.001)（高出 75%）在寒冷的早晚高峰时段，在某些地点有更大的增加。这种“冷启动”结果表明，结合最近的车辆驾驶历史和环境天气条件，结合对某些车辆排放控制系统工作温度范围的技术限制，会影响 NOx 排放，从而对城市环境中的空气质量产生不利影响。在某些气象条件下，冷启动排放的增加意味着空气污染导致的二氧化氮衍生的健康负担增加，其评估应考虑由于天气导致的车辆使用变化，从而改变个人暴露。