Carbon emission exposure is largely related to the number of vehicles passing through a particular area. The study performed by Akland, Hartwell, Johnson, and Whitmore concluded that citizens are exposed to elevated levels of CO when performing activities associated with transit and being in places that are in close proximity to vehicle exhaust, such as gas stations lots, highways, etc.
The study found that citizens of Denver are much more exposed to CO than citizens of Washington DC are, with a 10% exposure rate vs. 4%. This difference can be easily explained if we look at the Denver transportation system and compare it to Washington. Denver is the capital of one of the most populous states in the USA and is a massive transportation hub. A total of eight highways run through Denver, five of which are interstate highways. Washington DC, on the other hand, has none.
The last attempt at building a highway in Washington was in the 1960s, which never succeeded due to public protest. This means that the number of vehicles passing through Denver every day is much larger than that of Washington, which results in higher carbon emissions and higher rates of exposure. Other factors that contribute to higher CO emissions include the size of the population, population density, and the availability of public transport. Denver’s population density is almost four times higher than that of Washington, DC, meaning more people are likely to become exposed to elevated levels of CO.