Aerosol Acidity Measurement Using Colorimetry Coupled With a Reflectance UV-Visible Spectrometer

Abstract

In this study, aerosol acidity was measured using colorimetry integrated with a Reflectance UV-Visible spectrometer (C-RUV). An inorganic aerosol comprising NH 4 + −H + −SO 4 2− −H 2 O was generated using an atomizer and introduced into a 2-m 3 indoor Teflon film chamber. The produced aerosol was collected on the Tefloncoated glass fiber filter dyed with metanil yellow (MY) as an indicator for measuring proton concentrations in aerosol. A calibration curve for measuring aerosol acidity using the C-RUV technique was obtained through the relationship between the absorbance of the UV-Visible spectrum of the filter sample vs. theoretically calculated proton concentrations using the E-AIM Model II. To develop the C-RUV method under various humidities, the aerosol filter sample was mounted inside a small optical flow chamber controlled for humidity in situ. The humidity effect on the equilibrium thermodynamics of the indicator was theoretically described by inclusion of excess acidity (X) into the calibration curve. The calibration curve obtained from relatively highly acidic aerosols (e.g., H 2 SO 4 , NH 4 H 3 (SO 4 ) 2 , and (NH 4 ) 7 H 13 (SO 4 ) 10 ) was extrapolated to estimate proton concentrations for weakly acidic aerosols (e.g., NH 4 HSO 4 and (NH 4 ) 3 H(SO 4 ) 2 ), which is more relevant to the ambient aerosol acidity but has been poorly predicted with typical inorganic thermodynamic models due to the limited experimental data. The C-RUV technique of this study permits one to estimate aerosol acidity for a variety of compositions of the NH 4 + −H + −SO 4 2− −H 2 O system including both ammonia-poor and ammonia-rich sulfate aerosols.

Simulating the SOA formation of isoprene from partitioning and aerosol phase reactions in the presence of inorganics

“…The colorimetry integrated with reflectance UV-visible spectrometer (C-RUV) technique Li and Jang, 2012) was used to measure [H + ] (mol L −1 aerosol) in experiment SA2. The C-RUV technique utilizes a dyed filter to collect aerosol and act as an indicator for particle acidity.…”

“…Based on these results, it was assumed that presence of organics in isoprene SHMP SOA does not significantly influence the [H + ] from inorganic acids. Therefore, [H + ] is estimated for each time step by E-AIM II (Clegg et al, 1998) corrected for the ammonia-rich condition (Li and Jang, 2012) and RH. Then, [H + ] is diluted using the ratio of the inorganic volume to the total aerosol volume.…”

Modeling atmospheric mineral aerosol chemistry to predict heterogeneous photooxidation of SO<sub>2</sub>

“…In (Clegg et al, 1998;Wexler and Clegg, 2002). In this study, [H + ] is estimated by E-AIM II (Clegg et al, 1998;Wexler and Clegg, 2002;Clegg and Wexler, 2011) and corrected for the ammonia-rich condition Li and Jang, 2012). The reported uncertainty in [H + ] associated with the C-RUV method is ±18 %.…”

“…In AMAR, aerosol acidity ([H + ]) is estimated at each time step by E-AIM II (Clegg et al, 1998;Wexler and Clegg, 2002;Clegg and Wexler, 2011) corrected for the ammonia-rich condition Beardsley and Jang, 2016;Li and Jang, 2012) as a function of inorganic composition measured by a particle-into-liquid sampler coupled with ion chromatography (PILS-IC). When the ammonia-to-sulfate ratio is greater than 0.8, the prediction of [H + ] is corrected based on the method described by Li and Jang (2012). At high NO x levels, NO − 2 (aq) competes with S(IV) (aq) for the reaction with OH(aq), O 3 , or H 2 O 2 (Table S1) (Ma et al, 2008).…”

Fine particle pH for Beijing winter haze as inferred from different thermodynamic equilibrium models

“…The direct filter sampling approach is challenged by the nature of hydrogen ion in that its concentration in a solution does not scale in proportion to the level of dilution, and is also subject to sampling errors (Hennigan et al, 2015). A few studies have determined the pH of laboratory generated particles using colorimetry/spectrometry and Raman microspectroscopy (Li and Jang, 2012;Rindelaub et al, 2016;Craig et al, 2017), but such techniques have not been applied to ambient particles partly due to their much more complex chemical and physical 15 properties. Therefore, an indirect (or proxy) method-thermodynamic equilibrium modeling-has been widely used to estimate particle pH for many regions of the world (Bougiatioti et al, 2016;Guo et al, 2017a;Parworth et al, 2017;Murphy et al, 2017;Yao et al, 2007;Zhang et al, 2007).…”