Evidence for an increase in the ozone photochemical lifetime in the eastern United States using a regional air quality model

Abstract

Measures to control surface ozone rely on quantifying production attributable to local versus regional (upwind) emissions. Here we simulate the relative contribution of local (i.e., within a particular state) and regional sources of surface ozone in the eastern United States (66–94°W longitude) for July 2002, 2011, and 2018 using the Comprehensive Air‐quality Model with Extensions (CAMx). To determine how emissions and chemistry within the domain affect the production, loss, lifetime, and transport of trace gases, we initialize our model with identical boundary conditions in each simulation. We find that the photochemical lifetime of ozone has increased as emissions have decreased. The contribution of ozone from outside the domain (boundary condition ozone, BCO3) to local surface mixing ratios increases in an absolute sense by 1–2 ppbv between 2002 and 2018 due to the longer lifetime of ozone. The photochemical lifetime of ozone lengthens because the two primary gas phase sinks for odd oxygen (Ox ≈ NO2 + O3)—attack by hydroperoxyl radicals (HO2) on ozone and formation of nitrate—weaken with decreasing pollutant emissions. The relative role of BCO3 will also increase. For example, BCO3 represents 34.5%, 38.8%, and 43.6% of surface ozone in the Baltimore, MD, region during July 2002, 2011, and 2018 means, respectively. This unintended consequence of air quality regulation impacts attainment of the National Ambient Air Quality Standard for surface ozone because the spatial and temporal scales of photochemical smog increase; the influence of pollutants transported between states and into the eastern U.S. will likely play a greater role in the future.

The Story of Ever Diminishing Vehicle Tailpipe Emissions as Observed in the Chicago, Illinois Area

“…This has resulted in ozone levels that have improved in many areas of the country but areas such as Los Angeles are still predicted to remain above the standards for the foreseeable future . Because of the nonlinear nature of ozone chemistry, the ambient VOC/NO x mixing ratio is a critical parameter with a value of approximately 10–12 (as ppb C/ppb N) delineating a level of maximum ozone production. , This ratio decreased throughout the 90s and early 2000s along with vehicle HC emissions to less than half of these levels but has begun increasing as decreases in vehicle NO x emissions have followed. , In addition recent research suggest that mobile source HC emissions have declined to the point that volatile chemical products (pesticides, coatings, inks, adhesives, cleaners, and personal care products) now account for more than half of the urban VOC emissions . For VOC limited regions this will likely require new approaches for HC emissions reductions that go beyond additional mobile source standards.…”

“…35,36 This ratio decreased throughout the 90s and early 2000s along with vehicle HC emissions to less than half of these levels but has begun increasing as decreases in vehicle NO x emissions have followed. 37,38 In addition recent research suggest that mobile source HC emissions have declined to the point that volatile chemical products (pesticides, coatings, inks, adhesives, cleaners, and personal care products) now account for more than half of the urban VOC emissions. 39 For VOC limited regions this will likely require new approaches for HC emissions reductions that go beyond additional mobile source standards.…”

Top‐Down Estimates of NOx and CO Emissions From Washington, D.C.‐Baltimore During the WINTER Campaign

“…The SMOKE analysis predicted slightly higher afternoon CO (1,500 ± 500 mol s −1 ) and NO x (170 ± 20 mol s −1 ) emission rates compared to the interpolated, forward‐projected, temporally allocated NEI CO (~1,100 mol s −1 ) and NO x (~115 mol s −1 ) emission estimates. A step‐by‐step explanation of the scaling/temporal allocations conducted on the D.C.‐Balt emission inventories, as well as discussion of the SMOKE analysis (EPA, , ; Goldberg et al, , ; Houyoux & Vukovich, ; Kota et al, ; Vinciguerra et al, ), is provided in Text S4 and Figures S6 and S7.…”

“…WINTER 2015 CO and NO x emissions were also calculated from Sparse Matrix Operator Kernel Emissions (SMOKE) outputs based on the NEI-11, as described by Anderson et al (2014). The SMOKE analysis predicted slightly higher afternoon CO (1,500 ± 500 mol s À1 ) and NO x (170 ± 20 mol s À1 ) emission rates compared to the interpolated, forward-projected, temporally allocated NEI CO (~1,100 mol s À1 ) and NO x (~115 mol s À1 ) (EPA, 2014a(EPA, , 2014bGoldberg et al, 2015Goldberg et al, , 2016Houyoux & Vukovich, 1999;Kota et al, 2012;Vinciguerra et al, 2017), is provided in Text S4 and Figures S6 and S7.…”

Secondary organic aerosol production from local emissions dominates the organic aerosol budget over Seoul, South Korea, during KORUS-AQ

“…Note that although some SOA precursors are not emitted from combustion sources, such as volatile chemical products (McDonald et al, 2018), one can still define this ratio in an average sense for each megacity. It has been used previously for laboratory experiments (e.g., Gordon et al, 2013;Platt et al, 2013Platt et al, , 2017 and biomass burning (e.g., Akagi et al, 2012;Collier et al, 2016); however, to the best of the authors' knowledge, it has not been used for SOA production over a megacity. As noted above, CO has been typically used instead, given that it is always measured in pollution studies, and it typically has a higher signal-to-background ratio than CO 2 in urban areas.…”