Monitoring and apportioning sources of outdoor and indoor air quality using low-cost particulate matter sensors

Air quality is the leading environmental factor for public health globally. Source apportionment of air pollution is a key aspect of understand and ameliorating air quality problems. However, its use has been rather limited primarily due to the high cost that comes with instrument deployment. The emergence of low-cost sensors provides a new tool for assessing air quality and assigning sources within outdoor and indoor environments.

We have developed low-cost source apportionment techniques that can be used with single and multiple point measurements in outdoor environments. We have demonstrated its applicability for understanding sources at urban background sites, as well as assessing the pollution footprint of several industrial activities. The application of our methodology greatly improved our understanding of major pollution sources, by pinpointing and quantifying their effect in the surrounding area, at only a fraction of the cost of regulatory approaches. The information of the effect of any polluting activity, as well as the conditions that enhance or reduce it, is crucial information for the remediation of air quality problems.

Continuing our successful work on apportioning pollution in outdoor environments, we now focus on the indoor environment. Indoor environments can be particularly important because of the duration of time spent within them, and hence the potential for high exposure. These environments can be highly heterogenous, with different sources and concentrations varying from room to room. In our latest study, four low-cost sensors were deployed both inside and outside a typical family house close to Birmingham, UK. While the average PM concentrations in all rooms were within the latest World Health Organisation (WHO) guidelines, great variation was found on the PM concentrations among the rooms. Using the source apportionment methods the effect of the indoor and outdoor sources of particles was quantified. Up to 95% of the PM₁ was found to be from outdoor sources in all the rooms. This effect was reduced as particle size increased, though the outdoor sources were still contributing more than 65% of the PM_2.5 and up to 50% of the PM₁₀, depending on the room studied. These measurements allowed for the estimation of the average exposure of a work-at-home day. The implications on increased working from home will be discussed with respect to total exposure.

This study reveals new insights into the how different indoor and outdoor sources combine within households to contribute to total air pollution exposures. It highlights that total exposure is a function of the geographic situation of the household, the physical infrastructure of the household including filtration and appliances. This methodology will also be tested and used within the RI-URBANS pilot project to assess the air quality of the area surrounding the University of Birmingham. The presentation will finish with a roadmap on how low cost source apportionment can help to improve indoor and outdoor air quality.