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P a g e | 69 With great strides made in cleaning-up factory pollution the past half century, today we are talking about photochemical smog , which is formed by the reactivity of vehicle exhaust in the presence of sunlight. Vehicle exhaust consists primarily of CO and NO, which are quickly oxidized into CO 2 and NO 2 . Automobiles produce ~4 grams of CO 2 and ~0.3 grams of NOx per mile. 127 Line- haul trucks produce about 30% more of each; while heavy-duty trucks as much as for-times (4x). NOx has a GWP factor of as much as 60 or more CO 2 e. Vehicle CO and NO are referred to as primary pollutants because they set in motion a series of photochemical reactions that produce secondary pollutants . It is the secondary pollutants NO 2 and O 3 that are responsible for the build-up of smog. Atmospheric oxygen (O 2 ) and sunlight in the UV spectrum <400nm, cause the photochemical decomposition of NO 2 into photochemical smog: NO + O 2 – NO 2 + O NO 2 + UV – NO + O O + O 2 – O 3 Types of reactive nitrogen gases have a half-life as high as 100 to 150 years 128 and the EPA believes NOx concentrations from vehicles and near roadways are appreciably higher than those measured at monitors in the current EPA network. 129 In fact, near-road contaminations can be 2–3 times higher, 130 making road-level “breathing zones” uniquely attractive targets for managing mobile-sourced emissions including dangerous tropospheric ozone loads. Table 8 – Transportation CO 2 e Emissions by Type 131 Road 75% Aviation 13% Marine 11% Rail 1% Source: McKinsey & Co. 127 Bureau of Transportation Statistics, United States Department of Transportation. 128 EPA, Technical Bulletin: Nitrogen Oxides (NO x ), Why and How They are Controlled , November 1999. 129 Ibid. 130 EPA: Near Roadway Air Pollution and Health, Frequently Asked Questions EPA-420-F-14-014, www.epa.gov . 131 McKinsey & Co., The Net Zero Transition, what it would cost, what it could bring , January 2022.