LowEmissionAsphalt-136pg-WhitePaper-May2023

P a g e | 71 The catalytic role of NOx in the production of O 3 (smog) provides the most prominent contribution. Globally, the GWP of NOx is estimated 10 to 33 CO 2 e for the respective time horizons of 100 years and 20 years, 136 and is thereby comparable to that of methane (CH 4 ) by environmental chemists. NOx emission impact, however, is situational, influenced by load factors in dense urban areas, causing greenhouse effectivity to be substantially more intense. It is estimated that NOx concentrations in heavily trafficked regions exacerbate the greenhouse effect by as much as 23%. 137 In large cities, GWP estimates for NOx exceed 60 CO 2 e . 138 So O 3 is a dominant GHG associated with positive (warming) radiative forcing of our climate. 139 The RF of a given pollutant species is how we measure GWP. NOx has a net radiative flux of 0.35 Wm -2 (watts per square meter), 140 making it the third most impacting on climate change after CO 2 and CH 4 . NOx and photochemical smog are, of course, toxic and have known and direct serious impact on human health and are a major source of environmental inequities . The American Lung Association has concluded that: “ The burden of air pollution is not evenly shared. Poorer people and some racial and ethnic groups are among those who often face higher exposure to pollutants…” 141 owing to their proximity to major point-sources (industry, traffic, and airfields) for anthropogenic pollution. 136 Lammel G and Grabi H, Greenhouse effect of NOx, Environmental Science and Pollution Research (ESPR) , July 1995. 137 Lammel G and Grabi H. 138 Dahlmann K et al, Quantifying the contributions of individual NOx sources to the trend in ozone radiative forcing , DLR Institute for Atmospheric Physics, Oberpfaffenhofen, Germany, February 2011. 139 Derwent RG, Radiative forcing from surface NOx emissions: spatial and seasonal variations, Institute for Atmospheric and Environmental Science, University of Edinburgh 2007. 140 radiative forcing is the change in net, downward minus upward, radiative flux expressed in watts per square meter at the tropopause (top of atmosphere) due to the change in an external driver of climate change. 141 American Lung Association , Disparities in the Impact of Air Pollution , www.lung.org . “ The burden of air pollution is not evenly shared. Poorer people and some racial and ethnic groups are among those who often face higher exposure to pollutants…”