William L. Knight1, Matthew P. Fraser2, Pierre Herckes This email address is being protected from spambots. You need JavaScript enabled to view it.1 

1 School of Molecular Sciences, Arizona State University, Tempe, AZ 85287-1604, USA
2 School of Sustainable Engineering and the Built Environment, Arizona State University, Tempe, AZ 85287-1004, USA


Received: July 22, 2020
Revised: January 6, 2021
Accepted: January 7, 2021

 Copyright The Author(s). This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are cited.


Download Citation: ||https://doi.org/10.4209/aaqr.200431  

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Cite this article:

Knight, W.L., Fraser, M.P., Herckes, P. (2021). Impact of Misting Systems on Local Particulate Matter (PM) Levels. Aerosol Air Qual. Res. 21, 200431. https://doi.org/10.4209/aaqr.200431


HIGHLIGHTS

  • PM concentrations increase by a factor of 8 when evaporating misters are in use.
  • PM concentrations decrease with increasing distance from misting systems.
  • PM5 concentrations measured in public outdoor spaces with misters are high
  • Comparable to high pollution days in places like Los Angeles or Beijing.
  • Chloride and magnesium ions may be used as tracers of aerosolized drinking water from misters.
 

ABSTRACT


In hot, arid environments, many outdoor spaces are cooled by misting systems. These systems spray a fine mist of water droplets that cool down the surrounding air through the endothermic evaporation process. As water sources often contain dissolved minerals, the evaporating droplet may leave an airborne particulate matter (PM) residue. Currently there is no information available on the impact of misting systems on localized PM concentrations. In this study, PM concentrations are found to increase by a factor of 8 from ambient levels in the vicinity of a residential misting system in controlled experiments. These experiments show PM concentrations decrease with increasing distance from misting systems. Chemical data reveal that chloride and magnesium ions may be used locally as tracers of particles from misting systems as chloride may be subject to atmospheric transformation. The average chloride concentration was 71 µg m–3 in samples collected while the misting system was operational and below the detection limit (< 8.2 µg m–3) in samples collected when the misting system was off. The average magnesium concentration was 11.7 µg m–3 in samples when misting system was on and 0.23 µg m–3 in samples when misting system was off. Ambient measurements of PM10 in public places cooled by misting ranged from 102 ± 10 µg m–3 to 1470 ± 150 µg m–3, and PM2.5 ranged from 95 ± 10 µg m–3 to 990 ± 100 µg m–3. Calculations suggest that misting systems could potentially emit PM quantities on the order of a gram per hour in the respirable particle size range.


Keywords: Particulate matter, Atmospheric aerosols, Ion chromatography, Misting systems



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