Modelling the environmental justice of the spatial distribution of air quality

Abstract

Relationships between air pollution, health and deprivation potentially result in the highest cost to both the public and the government in terms of increased mortality and morbidity; hence establishing links between them is important and justifiable. The concept of Environmental Justice (EJ) questions whether certain socio-economic groups bear a disproportionate burden of environmental externalities, and whether policy and practice are equitable and fair. This research presents an innovative air quality modelling framework to map the EJ of the spatial distribution of air quality; and the impact of air quality management measures on existing EJ concerns. To assist in this goal, a modelling approached has been developed which enables the assessment of traffic management solutions that may create only subtle changes in the traffic flow regimes; and accurately assesses the impact of a reduction in vehicle kilometres travelled (VKT). Strong evidence of environmental injustice in the current distribution and production of poor air quality has been provided in the literature. However, the overwhelming majority of existing studies have concentrated on the analysis of current or historic associations. As a result their methodologies do not allow for the analysis of future strategies therefore, a gap exists in understanding the EJ implications of air quality strategies or schemes designed to improve air quality. Recent years have seen heightened political focus on policy and attempts to improve air quality. Whilst it is broadly suggested in the literature that improving air quality also will improve existing EJ concerns, evidence to date shows that even in situations where air quality is improving, the rate of concentration improvement is lowest for the poor. This research presents a suite of linked models of traffic, emission, dispersion, and geodemographic models (the modelling framework) that together allow not only more accurate assessment of the existing EJ situation to be established over using traditional techniques, but also the assessment of future air quality strategies and schemes designed to improve air quality which may improve or exacerbate the existing EJ relationship. ii The use of microsimulation traffic modelling in conjunction with an instantaneous emissions model (IEM) is a well-established emissions modelling technique. However, the use of IEMs is generally confined to exploration of emissions outputs and not the subsequent dispersion of emissions in order to determine air quality. This research successfully combines advanced microscale modelling techniques and applies them in the context of an EJ study in order to produce an original modelling framework capable of household level EJ analysis. This research has established that, at a city level, there is no linear relationship between air quality and deprivation in the North East cities of Durham, Newcastle and Gateshead. However, analysis of geodemographic data at the household and postcode levels has provided evidence of environmental injustice in air quality across all three study areas. Additionally, this research has explored the impact of reductions in VKT as a proposed air quality management measure. Thereby, the reductions required in VKT (over 2010 traffic flows) in one study area, Durham, have been established in order to meet both EU air quality limits and future carbon targets. Incremented 5% VKT reduction changes were made to the base-case 2010 scenario until all considered targets were met. Based on a 2010 vehicle fleet, a 50% reduction in traffic through Durham’s AQMA is required to meet all EU air quality targets. Similarly, a 25% reduction in VKT is required assuming a 2020 vehicle fleet, and by 2025 a 15% reduction in VKT would ensure Durham met its air quality targets. Moreover, a 10% reduction in VKT by 2020, and 25% reduction by 2025 would ensure carbon dioxide (CO2) reductions across the study area equal to those set out in the carbon budget. Furthermore, it has been established that the reductions in VKT to meet both EU air quality limits and future carbon targets eliminates the identified EJ issue in Durham. Moreover, if future VKT is constrained to 2010 levels, the spatial distribution of air quality will be environmentally just in both the 2020 and 2025 assessment years