422
Y. Qian and A. G. Russell
be affected under strongly acidic conditions [7]. In addition, pH have impact on
particle composition by control the partitioning of semi-volatile species (e.g., formic,
acetic, ammonia and nitrate). Higher acidity will help these species more in the gasphase. During the summer, this and other study showed that PM2.5 aerosol pH was
always in low level, between 1.5 and 3 in the southeastern U.S. [2]. Because of the
difficulties involved in the direct measurement of aerosol pH, different proxy methods
were used and discussed in estimating aerosol acidity level in recent studies [6, 8].
Those methods include ion balances, cation/anion molar ratio, and thermodynamic
models, but former two can be a poor reflect of H
+ as their relationship with pH
is not significant [2, 4, 9]. In overall, particle pH can be an important reference for
emission control strategies in the purpose of protecting human health [5]. Determine
the relationship between pH and species or emission source can help evaluate the
performance of current atmospheric model, help determine the control strategy, and
help understand some chemical mechanisms related to aerosol acidity.
67.2 Methods
SEARCH Network (The Southeastern Aerosol Research and Characterization Study)
[3] provided measurement data used in this study. 30 species and meteorological data
were collected from SEARCH database from 2009 to 2013. The monitoring site is
Jefferson Street (JST) (33.776°N, 84.413°W), represents urban Atlanta environment.
Aerosol pH represents the H
+ concentration in particle liquid water, as a log scale.
In this study, thermodynamic model ISORROPIA-II was used to make estimation of
aerosol pH value. ISORROPIA-II, a thermodynamic model, solve for the equilibrium
concentrations of NH 4
− –SO 4
2− –NO 3
− –Na
+ –Cl
− –Ca
2+ –K
+ –Mg
2+ aerosol system to
get H
+ concentration and liquid water content (LWC), under which aerosol pH can
be calculated.
By the use of measurement data and Chemical Mass Balance (CMB) model CMBGC, a widely used source apportionment model, daily PM 2.5 source contributions
were obtained. 9 source categories were included in this study: light-duty gas vehicles
(LDGV), heavy-duty diesel vehicles (HDDV), soil dust (SDUST), biomass burning
(BURN), coal fire power plant (CFPP), ammonium sulfate (AMSULF), ammonium
bisulfate (AMBSULF), ammonium nitrate (AMNITR), and secondary organic carbon (SOC).
67.3 Results
The daily pH time series from 2009 to 2013 for JST were presented in Fig. 67.1. Over
the study period, pH is relatively stable over 5 years with significant seasonal pattern
of lower in the summer (mean = 1.8) and higher in the winter (mean = 2.7). pH can
be averagely differed by about 1 unit. This kind of pattern can be driven by variation
Y. Qian and A. G. Russell
be affected under strongly acidic conditions [7]. In addition, pH have impact on
particle composition by control the partitioning of semi-volatile species (e.g., formic,
acetic, ammonia and nitrate). Higher acidity will help these species more in the gasphase. During the summer, this and other study showed that PM2.5 aerosol pH was
always in low level, between 1.5 and 3 in the southeastern U.S. [2]. Because of the
difficulties involved in the direct measurement of aerosol pH, different proxy methods
were used and discussed in estimating aerosol acidity level in recent studies [6, 8].
Those methods include ion balances, cation/anion molar ratio, and thermodynamic
models, but former two can be a poor reflect of H
+ as their relationship with pH
is not significant [2, 4, 9]. In overall, particle pH can be an important reference for
emission control strategies in the purpose of protecting human health [5]. Determine
the relationship between pH and species or emission source can help evaluate the
performance of current atmospheric model, help determine the control strategy, and
help understand some chemical mechanisms related to aerosol acidity.
67.2 Methods
SEARCH Network (The Southeastern Aerosol Research and Characterization Study)
[3] provided measurement data used in this study. 30 species and meteorological data
were collected from SEARCH database from 2009 to 2013. The monitoring site is
Jefferson Street (JST) (33.776°N, 84.413°W), represents urban Atlanta environment.
Aerosol pH represents the H
+ concentration in particle liquid water, as a log scale.
In this study, thermodynamic model ISORROPIA-II was used to make estimation of
aerosol pH value. ISORROPIA-II, a thermodynamic model, solve for the equilibrium
concentrations of NH 4
− –SO 4
2− –NO 3
− –Na
+ –Cl
− –Ca
2+ –K
+ –Mg
2+ aerosol system to
get H
+ concentration and liquid water content (LWC), under which aerosol pH can
be calculated.
By the use of measurement data and Chemical Mass Balance (CMB) model CMBGC, a widely used source apportionment model, daily PM 2.5 source contributions
were obtained. 9 source categories were included in this study: light-duty gas vehicles
(LDGV), heavy-duty diesel vehicles (HDDV), soil dust (SDUST), biomass burning
(BURN), coal fire power plant (CFPP), ammonium sulfate (AMSULF), ammonium
bisulfate (AMBSULF), ammonium nitrate (AMNITR), and secondary organic carbon (SOC).
67.3 Results
The daily pH time series from 2009 to 2013 for JST were presented in Fig. 67.1. Over
the study period, pH is relatively stable over 5 years with significant seasonal pattern
of lower in the summer (mean = 1.8) and higher in the winter (mean = 2.7). pH can
be averagely differed by about 1 unit. This kind of pattern can be driven by variation