The vanishing ozone weekday/weekend effect

Abstract

A national analysis of weekday/weekend ozone (O 3 ) differences conducted using 1997-1999 data found that many urban areas experienced at least 5% higher 8-hr maximum O 3 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 O 3 data shows that this phenomenon has mostly vanished. From 1997From -1999From to 2008From -2010, the percentage of U.S. monitoring sites that experienced 95th percentile daily 8-hr maximum average O 3 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 (AE5%) O 3 on weekdays and weekends. Similar trends were observed for the three other O 3 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 O 3 precursors declined significantly. However, a greater decline in nitrogen oxides (NO x ) emissions has caused an increase in the volatile organic compounds (VOC)/NO x emission ratios and it appears that this is the reason for the shift away from higher weekend O 3 concentrations.Implications: 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 NO x 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.

Observed trends in ground-level O<sub>3</sub> in Monterrey, Mexico, during 1993–2014: comparison with Mexico City and Guadalajara

“…Moreover, a change in NO x -limited O 3 production regime on weekends in the three urban areas seems unlikely since this would result in lower O 3 levels on weekends, which is not observed in any of the studied urban areas (Torres-Jardon et al, 2009). Wolff et al (2013) observed similar O 3 levels during weekdays and on weekends in several urban areas in the US despite lower O 3 precursor emissions over weekends. Furthermore, the number of sites in the US that exhibited a weekend effect decreased from ca.…”

Variability of Ozone Deposition Velocity Over a Mixed Suburban Temperate Forest

“…The resulting flux divergence recorded at our site (13 and 6% during winter and summer working-weeks compared to weekend as reference) is within the 0 and 25% deviance range from the surface fluxes for the critical zone of Damköhler number (0.1< DA <1), as demonstrated by Stella et al (2012). The chemical climate during the weekend, characterized by lower NO values, increased ratio of NO 2 /NO x leading to higher presence of O 3 , has been amply described by several authors (Fujita et al, 2003;Wolff et al, 2013). Due to a lower chemical sink during the weekends, flux measurements were less affected by flux divergence and hence, they could better represent the intrinsic O 3 deposition to the ecosystem.…”

Estimating Trends of Mean Monthly Ozone Emission in Urbanised Areas of Malaysia

“…This result obtained here is in agreement with the findings of NOAA, 2010 which reported a potential decrease in ground level ozone of the tropical areas during 2060 to 2100 because of the higher rate of emission of ozone depleting substances (ODS) with increasing human activities. Earlier study provided evidence for this finding (Wolff et al, 2013). For example, ozone concentration is lower in Athens compared to Helsinki and Mannheim (NOAA, 2010).…”