Spatiotemporal variability of nitrogen dioxide (NO₂) pollution in Manchester (UK) city centre (2017-2018) using a...

Nitrogen dioxide (NO₂) is linked to poor air quality and severe human health impacts, including respiratory and cardiovascular diseases and being responsible annually for approximately 23,500 premature deaths in the UK. Automated air quality monitoring stations continuously record pollutants in urban environments but are restricted in number (need for electricity, maintenance and trained operators), only record air quality proximal to their location and cannot document variability of airborne pollutants at finer spatial scales. As an alternative, passive sampling devices such as Palmes-type diffusion tubes can be used to assess the spatial variability of air quality in greater detail, due to their simplicity (e.g. small, light material, no electricity required) and suitability for long-term studies (e.g. deployable in large numbers, useful for screening studies). Accordingly, a one passive diffusion tube sampling approach has been adapted to investigate spatial and temporal variability of NO₂ concentrations across the City of Manchester (UK). Spatial and temporal detail was obtained by sampling 45 locations over a 12-month period (361 days, to include seasonal variability), resulting in 1080 individual NO₂ measurements. Elevated NO₂ concentrations, exceeding the EU/UK limit value of 40 µg m^-3, were recorded throughout the study period (N = 278; 26% of individual measurements), particularly during colder months and across a wide area including residential locations. Of 45 sampling locations, 24% (N = 11) showed annual average NO₂ above the EU/UK limit value, whereas 16% (N = 7) showed elevated NO₂ (> 40 µg m^-3) for at least 6 months of deployment. Highest NO₂ was recorded in proximity of highly trafficked major roads, with urban factors such as surrounding building heights also influencing NO₂ dispersion and distribution. This study demonstrates the importance of high spatial coverage to monitor atmospheric NO₂ concentrations across urban environments, to aid identification of areas of human health concern, especially in areas that are not covered by automated monitoring stations. This simple, reasonably cheap, quick and easy method, using a single-NO_x diffusion tube approach, can aid identification of NO₂ hotspots and provides fine spatial detail of deteriorated air quality. Such an approach can be easily transferred to comparable urban environments to provide an initial screening tool for air quality and air pollution, particularly where local automated air quality monitoring stations are limited. Additionally, such an approach can support air quality assessment studies, e.g. lichen or moss biomonitoring studies.