The sensitivity of PM<sub>2.5</sub> acidity to meteorological parameters and chemical composition changes: 10-year records from six Canadian monitoring sites
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Published:2019-07-19
Issue:14
Volume:19
Page:9309-9320
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ISSN:1680-7324
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Container-title:Atmospheric Chemistry and Physics
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language:en
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Short-container-title:Atmos. Chem. Phys.
Author:
Tao Ye,Murphy Jennifer G.
Abstract
Abstract. Aerosol pH is difficult to measure directly but can be calculated
if the chemical composition is known with sufficient accuracy and precision
to calculate the aerosol water content and the H+ concentration through
the equilibrium among acids and their conjugate bases. In practical terms,
simultaneous measurements of at least one semi-volatile constituent, e.g.
NH3 or HNO3, are required to provide a constraint on the
calculation of pH. Long-term records of aerosol pH are scarce due to the
limited monitoring of NH3 in conjunction with PM2.5. In this
study, 10-year (2007–2016) records of pH of PM2.5 at six eastern
Canadian sites were calculated using the E-AIM II model with the input of
gaseous NH3, gaseous HNO3 and major water-soluble inorganic ions
in PM2.5 provided by Canada's National Air Pollution Surveillance
(NAPS) Program. Clear seasonal cycles of aerosol pH were found with lower pH
(∼2) in summer and higher pH (∼3) in winter
consistently across all six sites, while the day-to-day variations of
aerosol pH were higher in winter compared to summer. Tests of the
sensitivity of aerosol pH to meteorological parameters demonstrate that the
changes in ambient temperature largely drive the seasonal cycle of aerosol
pH. The sensitivity of pH to chemical composition shows that pH has
different responses to the changes in chemical composition in different
seasons. During summertime, aerosol pH was mainly determined by temperature
with limited impact from changes in NHx or sulfate concentrations.
However, in wintertime, both meteorological parameters and chemical
composition contribute to the variations in aerosol pH, resulting in the
larger variation during wintertime. This study reveals that the sensitivity
of aerosol pH to chemical composition is distinctly different under
different meteorological conditions and needs to be carefully examined for
any particular region.
Publisher
Copernicus GmbH
Subject
Atmospheric Science
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