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.
Uniform description of non-Arrhenius temperature dependence of reaction rates, and a heuristic criterion for quantum tunneling vs classical non-extensive distribution