Jiayao Xu, Han Jiang, Haoran Zhao, Brent Stephens

  • Department of Civil, Architectural, and Environmental Engineering, Illinois Institute of Technology, Chicago, IL 60616, USA

Received: February 1, 2017
Revised: April 13, 2017
Accepted: June 9, 2017
Download Citation: ||https://doi.org/10.4209/aaqr.2017.02.0063  

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Cite this article:
Xu, J., Jiang, H., Zhao, H. and Stephens, B. (2017). Mobile Monitoring of Personal NOx Exposures during Scripted Daily Activities in Chicago, IL. Aerosol Air Qual. Res. 17: 1999-2009. https://doi.org/10.4209/aaqr.2017.02.0063


  • Mobile NO/NO2/NOx monitoring was conducted during scripted activities in Chicago, IL.
  • The highest median concentrations were in indoor and transportation environments.
  • Median concentrations in transportation locations were highest on regional trains.
  • Correlations between personal measurements and ambient monitors were very low.
  • Personal monitoring is critical for accurately assessing personal exposure to NOx.



Elevated ambient concentrations of nitrogen oxides (NOx), including nitric oxide (NO) and nitrogen dioxide (NO2), are associated with a wide range of adverse human health effects. Most studies have investigated these associations using ambient NO2/NOx measurements from fixed-site monitors or modeled ambient NO2/NOx concentrations. However, the majority of personal exposures to NO2/NOx occur in a variety of different microenvironments in which people spend most of their time. Previous studies have reported widely varying correlations between personal exposures and ambient NO2/NOx concentrations over various timescales. To add to the knowledge base of how personal NO/NO2/NOx exposures vary spatially, temporally, and within different microenvironments in an urban environment, we conducted roll-around mobile monitoring of NO/NO2/NOx with 1-minute resolution during 14 days of scripted activities in and around Chicago, IL. Activities involved time spent in three primary microenvironments: outdoors, indoors inside various building types, and in multiple modes of transportation including walking, personal vehicle, and public transit. Measurement were conducted at a higher time resolution than most prior microenvironmental monitoring studies using a recently developed direct UV absorbance NO/NO2/NOx monitor that is designed to minimize interferences that have been observed in some field campaigns using chemiluminescence monitors. The individual microenvironmental categories with the highest median NOx concentrations included four indoor environments and a variety of public transit environments. The individual transportation microenvironments with the highest median NOx concentrations were found aboard regional trains, largely driven by high NO from diesel locomotives. Correlations between microenvironmental NO/NO2/NOx measurements and simultaneous records from the nearest ambient monitor were extremely low, with coefficients of determination below 0.05 for each NOx constituent. These data further illustrate the limitations of relying on ambient site regulatory monitors to characterize personal NO/NO2/NOx exposures and provide further evidence that personal monitoring is critical for accurately assessing personal exposure to NOx.

Keywords: Nitrogen oxides; Human exposure; Personal exposure; Mobile samplers; Indoor air pollution

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