Air Improvement Resource, Inc., 47298 Sunnybrook Lane, Suite 103, Novi, MI, 48374, USA.
J Air Waste Manag Assoc. 2013 Mar;63(3):292-9. doi: 10.1080/10962247.2012.749312.
A national analysis of weekday/weekend ozone (O3) differences conducted using 1997-1999 data found that many urban areas experienced at least 5% higher 8-hr maximum O3 concentrations on weekends than on weekdays even though emissions of precursors were significantly lower on weekends. This phenomenon was observed mostly in urban areas in the Northeast, Midwest, and coastal California. A similar analysis using 2008-2010 O3 data shows that this phenomenon has mostly vanished. From 1997-1999 to 2008-2010, the percentage of U.S. monitoring sites that experienced 95th percentile daily 8-hr maximum average O3 concentration on weekends that were 5% or more higher than on weekdays declined from about 35% to less than 5%. At the same time the percentage of sites that experienced higher weekday concentrations increased from 3% to about 27%. The majority (68%) of the sites, however exhibited little sensitivity to the weekday/weekend emission changes as they had similar (+/- 5%) O3 on weekdays and weekends. Similar trends were observed for the three other O3 metrics examined: the 95th percentile of the 1-hr maximum and the April-September means of the 1-hr and 8-hr daily maxima. Over this time period, U.S. emissions of O3 precursors declined significantly. However, a greater decline in nitrogen oxides (NOx) emissions has caused an increase in the volatile organic compounds (VOC)/NOx emission ratios and it appears that this is the reason for the shift away from higher weekend O3 concentrations.
In areas where weekend emissions of ozone precursors are lower than on weekdays because of mainly lower motor vehicle emissions, an inadvertent test of ozone control strategies occurs. Such a test provides information on how control strategies that produce emission changes similar to those that occur on weekends affect ozone concentrations. In the late 1990s, lower NOx emissions on weekends resulted in higher levels of ozone in many urban areas. Emission controls that have been enacted since then appear to have eliminated that phenomenon in most urban areas. However, most areas now indicate that weekend emission reductions now have little effect on ozone concentrations at most sites.
使用 1997-1999 年的数据进行的全国范围内的工作日/周末臭氧（O3）差异分析发现，即使周末的前体物排放量明显较低，许多城市地区在周末的 8 小时最大 O3 浓度仍至少高出 5%。这种现象主要出现在美国东北部、中西部和加利福尼亚沿海地区的城市地区。使用 2008-2010 年 O3 数据进行的类似分析表明，这种现象已经基本消失。从 1997-1999 年到 2008-2010 年，经历周末 95 百分位日 8 小时最大平均 O3 浓度比工作日高出 5%或更多的美国监测站点比例从约 35%下降到不足 5%。与此同时，经历更高工作日浓度的站点比例从 3%增加到约 27%。然而，大多数站点（68%）对工作日/周末排放变化的敏感性较低，因为它们在工作日和周末的 O3 浓度相似（+/-5%）。对于另外三个检查的 O3 指标，也观察到了类似的趋势：1 小时最大的 95 百分位值、1 小时和 8 小时每日最大的 4 月至 9 月平均值。在此期间，美国的 O3 前体物排放量显著下降。然而，氮氧化物（NOx）排放量的大幅下降导致挥发性有机化合物（VOC）/NOx 排放比增加，似乎这就是周末 O3 浓度升高的原因。
在由于主要是机动车排放量较低，臭氧前体物周末排放量低于工作日的地区，会无意中对臭氧控制策略进行测试。这样的测试提供了有关控制策略产生类似于周末发生的排放变化如何影响臭氧浓度的信息。在 20 世纪 90 年代末，周末的 NOx 排放量较低导致许多城市地区的臭氧水平升高。自那时以来实施的排放控制措施似乎已经消除了大多数城市地区的这种现象。然而，现在大多数地区表明，周末减排现在对大多数站点的臭氧浓度几乎没有影响。
