Digging Deep: Neighbourhood air quality has spill over effects beyond what was previously thought

That air pollution impacts health is hardly news. Previous studies attest to the fact that air quality, along with other health indicators, further feed into – and even explain – socioeconomic inequalities that already ex. Studies in United States have shown that minority-poor neighbourhoods experience higher pollution levels than White-nonpoor ones, which reflects in their health outcomes. Not only that, Sharkey et al. (2014) show how most of these ‘environmentally disadvantaged’ areas tend to be clustered and ghettoised together, alienating them even further from areas with a better air quality or simply more economic opportunities.
But, invariably, most studies mapping the effects of air pollution on an individual’s health in terms of the neighbourhood s/he lives in, and the adjoining areas. Therein lies a catch: individuals living in an environmentally disadvantaged area that has high air pollution levels do not spend all their time there. Recent studies show that they may well spend time beyond their residential areas and the adjacent ones, often travelling to dant areas for work or leisure. If the area they frequent for work or leisure also has high air pollution levels, it reduces the impact living in an environmentally disadvantaged neighbourhood. On the other hand, if that area has high air pollution levels, it only worsens it further.
Moreover, one also needs to realise that these movements, although individual, are not necessarily individual driven. In other words, these networks and flows are dependent not only on individual choices but institutional and social connections. Therefore, these flows are well document at the level of a community than just at the level of an individual.

Noli Brazil, a human ecolog from the University of California, Davis, sought to address this question tapping into anonymised cellphone data on the movement of a person along with air quality indices. The cellphone data here was provided SafeGraph, an organisation that monitors and maintains a compendium of geospatial datasets for more than forty million American smartphones. This is used as a proxy for urban mobility patterns at an individual level for 88 most populated American cities. This was supplemented air quality data provided Environment Protection Agency (EPA) on particulate matter concentration (PM 2.5). The parameter measures particles smaller than 2.5 µm in diameter that can be inhaled in terms of µg/m³. Finally, the resultant datapoints were examined from the standpoint of income levels (poor v nonpoor) and race (White, Black, Hispanic, Asian etc.).
This exercise was conducted at three spatial levels: the residential neighbourhood, the neighbourhoods adjacent to the residence and the neighbourhoods travelled-to for work/leisure/social commitments. These are labelled as the ‘residential,’ ‘adjacent,’ and the ‘network’ levels.
Brazil found that, ‘on average the neighbourhoods that residents from non-White communities travel to have higher PM2.5 levels than the neighbourhoods connected to White communities. The PM2.5 levels in Hispanic, Black, and Asian networks are 12.4%, 11.5%, and 11.5% higher than the levels in White networks (7.81), respectively.’ Similar results were found in terms of income levels, in that the areas where people from poorer neighbourhoods commute to have 6.8% higher PM2.5 levels than areas visited people from nonpoor neighbourhoods.
Corroborating prior epidemiological studies, results non only indicate that neighbourhoods where Hispanic, Black and Asian groups live are consently marked higher PM 2.5 levels compared to white neighbourhoods. While PM2.5 levels in white neighbourhoods were 7.81, those in Hispanic, Black and Asian neighbourhoods were 8.85, 8.72 and 8.74 consently. Furthermore, and predictably so, these neighbourhoods are surrounded those with similar PM2.5 levels. Bringing to fore disparities across race/ethnicity and income-level groups, Brazil finds that average PM2.5 levels ‘5.9, 5.9, and 5.2% lower in White nonpoor residential, adjacent, and network neighbourhoods, respectively, than in poor neighbourhoods.’ The advantage of nonpoor neighbourhoods over poor ones, in terms of air pollution risk, was far less pronounced for other ethnic groups like Hispanics, Blacks and Asians.

Out of the three spatial/ecological levels examined here, the third, ‘network’ level, becomes significant not only because it is seldom considered in most studies on urban mobility, but also because – as this study finds – it turns out that people from Black, Hispanic and Asian neighbourhoods travel to dant areas just as much as their counterparts from White neighbourhoods. In fact, Black people travel even further dances than White people do, while commuting dances between Asians, Hispanics and White people are somewhat similar. Examining the ‘network’ level reveals more nuanced patterns as well. For instance, while Hispanic neighbourhoods – poor or nonpoor – carry the most exposure risk in terms of air pollution, but their residents travel to areas that have lower PM2.5 levels. This is not true for Black or Asian groups, which commute to areas that have an exposure risk similar-to or higher-than their residential neighbourhoods; there making their disparities with White poor/nonpoor groups more pronounced.
The key takeaway that this exercise gives us is that disparities in access to clean air, in terms of both ethnic background as well as the income level, extend well beyond the places where people live and that their ‘networks’ play a major role. If anything, its influence had been ‘underestimated’ in previous studies. Brazil hopes that ‘Adopting a network perspective can also increase efficiency in resource allocation focusing interventions in the most polluted and visited neighbourhoods within a mobility network.’