Abstract Control on emissions of nitrogen oxides (NOx) in the United States of America have led to reductions in concentrations in urban areas by up to a factor of two in the last decade. The Air Quality System monitoring network provides surface measurements of concentrations at hourly resolution over multiple years, revealing variations at the annual, seasonal, day of week and diurnal time scales. A multiple linear regression model was used to estimate the temporal profiles in the NOx concentrations as well as the impact of meteorology, ozone concentrations, and boundary layer heights. The model is applied to data from 2005 to 2016 available at 6 sites in Chicago, Illinois. Results confirm the 50% decrease in NOx over the length of the time series. The weekend effect is found to be stronger in more commercial areas, with 32% reductions on Saturdays and 45% on Sundays and holidays; and weaker in more residential areas with 20% reductions on Saturdays and 30% reductions on Sundays. Weekday diurnal profiles follow a double hump with emission peaks during the morning and afternoon rush hours, but only a shallow drop during the middle day. Difference in profiles from the 6 sites suggest that there are different emission profiles within the urban area. Diurnal profiles on Saturdays have less variation throughout the day and more emissions in the evening. Sundays are very different from both weekdays and Saturdays with a gradual increase until the early evening. The results suggest that in addition to vehicle type and vehicle miles traveled, vehicle speed and congestion must be taken into account to correctly quantify morning rush hour emissions and the weekend effect.

中文翻译：

---

芝加哥每小时监测数据得出的 NO x 排放量的城市级变化

摘要 在过去十年中，美国对氮氧化物 (NOx) 排放的控制导致城市地区的浓度降低了两倍。空气质量系统监测网络提供多年的每小时分辨率的表面浓度测量值，揭示年度、季节、星期几和昼夜时间尺度的变化。使用多元线性回归模型来估计 NOx 浓度的时间分布以及气象、臭氧浓度和边界层高度的影响。该模型应用于伊利诺伊州芝加哥 6 个站点 2005 年至 2016 年的数据。结果证实了在时间序列长度上 NOx 减少了 50%。发现周末效应在更多商业区更强，周六降价32%，周日和节假日降价45%；较弱的住宅区，周六降幅为 20%，周日降幅为 30%。工作日的昼夜剖面遵循双峰，在上午和下午的高峰时段排放峰值，但在中午仅略有下降。6 个地点分布的差异表明市区内有不同的排放分布。星期六的昼夜剖面全天变化较小，晚上排放较多。周日与平日和周六有很大不同，逐渐增加直到傍晚。结果表明，除了车辆类型和车辆行驶里程外，