scholarly journals Interactive comment on “NOx emissions, isoprene oxidation pathways, vertical mixing, and implications for surface ozone in the Southeast United States” by Travis et al.

2016 ◽  
Author(s):  
Anonymous
Keyword(s):  
United States ◽  
Surface Ozone ◽  
Vertical Mixing ◽  
Nox Emissions ◽  
Southeast United States ◽  
Isoprene Oxidation

scholarly journals NO<sub>x</sub> emissions, isoprene oxidation pathways, vertical mixing, and implications for surface ozone in the Southeast United States

2016 ◽  
Author(s):  
Katherine R. Travis ◽  
Daniel J. Jacob ◽  
Jenny A. Fisher ◽  
Patrick S. Kim ◽  
Eloise A. Marais ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Surface Ozone ◽  
Vertical Mixing ◽  
Satellite Observations ◽  
Oxidation Products ◽  
Large Contribution ◽  
Nox Emissions ◽  
Tropospheric No2 ◽  
Isoprene Oxidation ◽  
Southeast Us

Abstract. Ozone pollution in the Southeast US involves complex chemistry driven by emissions of anthropogenic nitrogen oxide radicals (NOx ≡ NO + NO2) and biogenic isoprene. Model estimates of surface ozone concentrations tend to be biased high in the region and this is of concern for designing effective emission control strategies to meet air quality standards. We use detailed chemical observations from the SEAC4RS aircraft campaign in August and September 2013, interpreted with the GEOS-Chem chemical transport model (CTM) at 0.25°×0.3125° horizontal resolution, to better understand the factors controlling surface ozone in the Southeast US. We find that the National Emission Inventory (NEI) for NOx from the US Environmental Protection Agency (EPA) is too high in the Southeast and nationally by 50 %. This is demonstrated by SEAC4RS observations of NOx and its oxidation products, by surface network observations of nitrate wet deposition fluxes, and by OMI satellite observations of tropospheric NO2 columns. Upper tropospheric NO2 from lightning makes a large contribution to the satellite observations that must be accounted for when using these data to estimate surface NOx emissions. Aircraft observations of upper tropospheric NO2 are higher than simulated by GEOS-Chem or expected from NO-NO2-O3 photochemical stationary state. NOx levels in the Southeast US are sufficiently low that only half of isoprene oxidation proceeds by the high-NOx pathway to produce ozone; this fraction is only moderately sensitive to changes in NOx emissions because isoprene and NOx emissions are spatially segregated. GEOS-Chem with reduced NOx emissions provides an unbiased simulation of ozone observations from the aircraft and from ozonesondes, and reproduces the observed ozone production efficiency in the boundary layer as derived from a regression of ozone and NOx oxidation products. However, the model is still biased high by 8 ± 13 ppb relative to observed surface ozone in the Southeast US. Ozonesondes launched during midday hours show a 7 ppb ozone decrease from 1.5 km to 0.2 km altitude, whereas GEOS-Chem has no such gradient because of efficient boundary layer mixing. We conclude that model biases in simulating surface ozone over the Southeast US may be due to a combination of excessive NOx emissions and excessive boundary layer vertical mixing.

scholarly journals Decadal changes in summertime reactive oxidized nitrogen and surface ozone over the Southeast United States

2018 ◽  
Vol 18 (3) ◽  
pp. 2341-2361 ◽  
Author(s):  
Jingyi Li ◽  
Jingqiu Mao ◽  
Arlene M. Fiore ◽  
Ronald C. Cohen ◽  
John D. Crounse ◽  
...  
Keyword(s):  
Climate Model ◽  
Surface Ozone ◽  
Regional Scale ◽  
Nox Emissions ◽  
Alkyl Nitrates ◽  
Southeast United States ◽  
Ground Measurement ◽  
Southeast Us ◽  
June July ◽  
Relative Change

Abstract. Widespread efforts to abate ozone (O3) smog have significantly reduced emissions of nitrogen oxides (NOx) over the past 2 decades in the Southeast US, a place heavily influenced by both anthropogenic and biogenic emissions. How reactive nitrogen speciation responds to the reduction in NOx emissions in this region remains to be elucidated. Here we exploit aircraft measurements from ICARTT (July–August 2004), SENEX (June–July 2013), and SEAC4RS (August–September 2013) and long-term ground measurement networks alongside a global chemistry–climate model to examine decadal changes in summertime reactive oxidized nitrogen (RON) and ozone over the Southeast US. We show that our model can reproduce the mean vertical profiles of major RON species and the total (NOy) in both 2004 and 2013. Among the major RON species, nitric acid (HNO3) is dominant (∼ 42–45 %), followed by NOx (31 %), total peroxy nitrates (ΣPNs; 14 %), and total alkyl nitrates (ΣANs; 9–12 %) on a regional scale. We find that most RON species, including NOx, ΣPNs, and HNO3, decline proportionally with decreasing NOx emissions in this region, leading to a similar decline in NOy. This linear response might be in part due to the nearly constant summertime supply of biogenic VOC emissions in this region. Our model captures the observed relative change in RON and surface ozone from 2004 to 2013. Model sensitivity tests indicate that further reductions of NOx emissions will lead to a continued decline in surface ozone and less frequent high-ozone events.

scholarly journals The mechanisms and meteorological drivers of the summertime ozone–temperature relationship

2019 ◽  
Vol 19 (21) ◽  
pp. 13367-13381 ◽  
Author(s):  
William C. Porter ◽  
Colette L. Heald
Keyword(s):  
United States ◽  
Temperature Dependence ◽  
Transport Model ◽  
Surface Ozone ◽  
The United States ◽  
Reaction Rates ◽  
Temperature Relationship ◽  
Nox Emissions ◽  
Temperature Dependent ◽  
Temperature Correlation

Abstract. Surface ozone (O3) pollution levels are strongly correlated with daytime surface temperatures, especially in highly polluted regions. This correlation is nonlinear and occurs through a variety of temperature-dependent mechanisms related to O3 precursor emissions, lifetimes, and reaction rates, making the reproduction of temperature sensitivities – and the projection of associated human health risks – a complex problem. Here we explore the summertime O3–temperature relationship in the United States and Europe using the chemical transport model GEOS-Chem. We remove the temperature dependence of several mechanisms most frequently cited as causes of the O3–temperature “climate penalty”, including PAN decomposition, soil NOx emissions, biogenic volatile organic compound (VOC) emissions, and dry deposition. We quantify the contribution of each mechanism to the overall correlation between O3 and temperature both individually and collectively. Through this analysis we find that the thermal decomposition of PAN can explain, on average, 20 % of the overall O3–temperature correlation in the United States. The effect is weaker in Europe, explaining 9 % of the overall O3–temperature relationship. The temperature dependence of biogenic emissions contributes 3 % and 9 % of the total O3–temperature correlation in the United States and Europe on average, while temperature-dependent deposition (6 % and 1 %) and soil NOx emissions (10 % and 7 %) also contribute. Even considered collectively these mechanisms explain less than 46 % of the modeled O3–temperature correlation in the United States and 36 % in Europe. We use commonality analysis to demonstrate that covariance with other meteorological phenomena such as stagnancy and humidity can explain the bulk of the remainder of the O3–temperature correlation. Thus, we demonstrate that the statistical correlation between O3 and temperature alone may greatly overestimate the direct impacts of temperature on O3, with implications for the interpretation of policy-relevant metrics such as climate penalty.

scholarly journals The mechanisms and meteorological drivers of the ozone–temperature relationship

2019 ◽  
Author(s):  
William C. Porter ◽  
Colette L. Heald
Keyword(s):  
United States ◽  
Temperature Dependence ◽  
Transport Model ◽  
Surface Ozone ◽  
The United States ◽  
Reaction Rates ◽  
Temperature Relationship ◽  
Nox Emissions ◽  
Temperature Dependent ◽  
Temperature Correlation

Abstract. Surface ozone (O3) pollution levels are strongly correlated with daytime surface temperatures, especially in highly polluted regions. This correlation is nonlinear and occurs through a variety of temperature dependent mechanisms related to O3 precursor emissions, lifetimes, and reaction rates, making the reproduction of temperature sensitivities – and the projection of associated human health risks – a complex problem. Here we explore the summertime O3–temperature relationship in the United States and Europe using the chemical transport model GEOS-Chem. We remove the temperature dependence of several mechanisms most frequently cited as causes of the O3–temperature climate penalty, including: PAN decomposition, soil NOx emissions, biogenic VOC emissions, and dry deposition. We quantify the contribution of each mechanism to the overall correlation between O3 and temperature both individually and collectively. Through this analysis we find that the thermal decomposition of PAN can explain, on average, 20 % of the overall O3–temperature correlation in the United States. The effect is weaker in Europe, explaining 9 % of the overall O3–temperature relationship. The temperature dependence of biogenic emissions contributes 3 % and 9 % of the total O3–temperature correlation in the United States and Europe on average, while temperature dependent deposition (6 % and 1 %) and soil NOx emissions (10 % and 7 %) also contribute. Even considered collectively these mechanisms explain less than 46 % of the modeled O3–temperature correlation in the United States and 36 % in Europe. We use commonality analysis to demonstrate that covariance with other meteorological phenomena such as stagnancy and humidity can explain the bulk of the remainder of the O3–temperature correlation. Thus, we demonstrate that the statistical correlation between O3 and temperature alone may greatly overestimate the direct impacts of temperature on O3, with implications for the interpretation of policy-relevant metrics such as climate penalty.

scholarly journals Effects of temperature-dependent NO<sub>x</sub> emissions on continental ozone production

2017 ◽  
Author(s):  
Paul S. Romer ◽  
Kaitlin C. Duffey ◽  
Paul J. Wooldridge ◽  
Eric Edgerton ◽  
Karsten Baumann ◽  
...  
Keyword(s):  
Surface Ozone ◽  
Ozone Production ◽  
Climate Feedback ◽  
Nox Emissions ◽  
Southeast United States ◽  
Average Temperature ◽  
Ozone Concentrations ◽  
Effects Of Temperature ◽  
Positive Climate

Abstract. Surface ozone concentrations are observed to increase with rising temperatures, but the mechanisms responsible for this effect in rural and remote continental regions remain uncertain. Better understanding of the effects of temperature on ozone is crucial to understanding global air quality and how it may be affected by climate change. We combine measurements from a focused ground campaign in summer 2013 with a long-term record from a forested site in the rural southeast United States to examine how daily average temperature affects ozone production. We find that changes to local chemistry are key drivers of increased ozone concentrations on hotter days, with integrated daily ozone production increasing by 2.3 ppb C−1. Nearly half of this increase is attributable to temperature-driven increases in emissions of nitrogen oxides (NOx), most likely by soil microbes. The increase of soil NOx emissions with temperature suggests that ozone will continue to increase with temperature in the future, even as direct anthropogenic NOx emissions decrease dramatically. The links between temperature, soil NOx, and ozone form a positive climate feedback.

Positive but variable sensitivity of August surface ozone to large-scale warming in the southeast United States

2015 ◽  
Vol 5 (5) ◽  
pp. 454-458 ◽  
Author(s):  
Tzung-May Fu ◽  
Yiqi Zheng ◽  
Fabien Paulot ◽  
Jingqiu Mao ◽  
Robert M. Yantosca
Keyword(s):  
United States ◽  
Large Scale ◽  
Surface Ozone ◽  
Southeast United States ◽  
Variable Sensitivity
Sign in / Sign up

Export Citation Format

Share Document