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Differential Probability Functions for Investigating Long-term Changes in Local and Regional Air Pollution Sources

Category: Urban Air Quality

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DOI: 10.4209/aaqr.2018.09.0327

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Mauro Masiol 1, Stefania Squizzato1, Meng-Dawn Cheng2, David Q. Rich1, Philip K. Hopke 1,3

  • 1 Department Public Health Sciences, University of Rochester Medical Center, Rochester, NY 14642, USA
  • 2 Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
  • 3 Center for Air Resources Engineering and Science, Clarkson University, Potsdam, NY 13699, USA


Emission changes over time are visualized using conditional probability differences.
Local source changes are identified with differential conditional bivariate probabilities.
Regional changes are shown by differential potential source contribution function.
These methods have been applied to PM components measured in Rochester, NY.


Conditional probability functions are commonly used for source identification purposes in air pollution studies. CBPF (conditional bivariate probability function) categorizes the probability of high concentrations being observed at a location by wind direction/speed and aim to investigate the directionality of local sources. PSCF (potential source contribution function), a trajectory-ensemble method, allows the identification of the source regions most likely to be associated with high measured concentrations. However, these techniques do not allow a direct identification of areas where changes in emissions have occurred. This study presents an extension of conditional probability methods in which the differences between conditional probability values for temporally different sets of data can be used to explore changes in emissions from source locations. The differential CBPF and differential PSCF were tested using a long-term series of air quality data (12 years; 2005/2016) collected in Rochester, NY. The probability functions were computed for each of 4 periods that represent known changes in emissions. Correlation analyses are also performed over the results to find pollutants undergoing similar changes in local and regional sources. The differential probability functions permitted the identification of major changes in local and regional emission locations. In Rochester, changes in local air pollution were related to the shutdown of a large coal power plant (SO2) and to the abatement measures applied to road and off-road traffic (primary pollutants). The concurrent effects of these changes in local emissions are also linked to decreases in nucleation mode particles. Changes in regional source areas were related to the decreases in secondary inorganic aerosol and organic carbon. The differential probabilities for sulfate, and nitrate, and organic aerosol were consistent with differences in the available National Emission Inventory annual emission values. Changes in the black carbon source areas were highly correlated with those of PM2.5 mass.


Differential probability functions Long-term trends Air pollution

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