AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
A Direct Method for Measuring the pH of Individual Aerosol Particles Using Raman Microspectroscopy
JOEL RINDELAUB, Amy Bondy, Rebecca Craig, Paul Shepson, Andrew Ault, Purdue University
Abstract Number: 189 Working Group: Instrumentation and Methods
Abstract Currently, there is a great need for the direct measurement of aerosol pH, due to the impact of acidic aerosols on environmental health and climate. Deposition of acidic particulate matter can negatively affect ecosystems while the inhalation of acidic particles has been linked to serious health issues. Also, many aerosol phase chemical processes, such as hydrolysis reactions and organosulfate formation, are highly dependent on particle acidity and may influence a particle’s ability to uptake water. Common methods of estimating aerosol pH are often indirect and can also jeopardize the integrity of samples, as in the case of filter collection methods. In addition, current thermodynamic models used to predict aerosol pH, such as the E-AIM and ISORROPIA-II, are frequently in disagreement with laboratory methods, calling for more refined techniques for the measurement of aerosol acidity. Thus, we developed a non-destructive spectroscopic method capable of directly measuring the pH of individual aerosol particles. The pHs of several laboratory-generated particles were measured as a function of relative humidity and aerosol composition at ambient pressure and temperature. We use Raman microspectroscopy to identify the ratios of peaks representing acids in different protonation states, which are clearly distinguishable in vibrational spectra. Results indicate that laboratory-generated particles may be much more acidic than previously estimated, providing important information into the conditions that govern aerosol phase processing. This technique also has the potential for pH measurement within ambient particles.