Volatility and Oxidative Aging of Aqueous Maleic Acid Aerosol Droplets and the Dependence on Relative Humidity

Abstract

The microphysical structure and heterogeneous oxidation by ozone of single aerosol particles containing maleic acid (MA) has been studied using aerosol optical tweezers and cavity enhanced Raman spectroscopy. The evaporation rate of MA from aqueous droplets has been measured over a range of relative humidities and the pure component vapor pressure determined to be (1.7 ± 0.2) × 10(-3) Pa. Variation in the refractive index (RI) of an aqueous MA droplet with relative humidity (RH) allowed the subcooled liquid RI of MA to be estimated as 1.481 ± 0.001. Measurements of the hygroscopic growth are shown to be consistent with equilibrium model predictions from previous studies. Simultaneous measurements of the droplet composition, size, and refractive index have been made during ozonolysis at RHs in the range 50-80%, providing insight into the volatility of organic products, changes in the droplet hygroscopicity, and optical properties. Exposure of the aqueous droplets to ozone leads to the formation of products with a wide range of volatilities spanning from involatile to volatile. Reactive uptake coefficients show a weak dependence on ozone concentration, but no dependence on RH or salt concentration. The time evolving RI depends significantly on the RH at which the oxidation proceeds and can even show opposing trends; while the RI increases with ozone exposure at low relative humidity, the RI decreases when the oxidation proceeds at high relative humidity. The variations in RI are broadly consistent with a framework for predicting RIs for organic components published by Cappa et al. ( J. Geophys. Res. 2011 , 116 , D15204 ). Once oxidized, particles are shown to form amorphous phases on drying rather than crystallization, with slow evaporation kinetics of residual water.

Heterogeneous chemistry and reaction dynamics of the atmospheric oxidants, O3, NO3, and OH, on organic surfaces

“…82,93 Additionally, Reid and coworkers investigated oxidative aging of aerosol particles containing environmentally relevant organic acids using optical tweezers and cavity enhanced ringdown spectroscopy. 94,95 For mixed NaCl/oleic acid particles, they report an uptake coefficient of 2.3 Â 10…”

Characterization of organic residues of size‐resolved fog droplets and their atmospheric implications

“…The dominance of semivolatile materials in residual OM in spite of overall high O/C ratios is not entirely surprising considering that laboratory studies suggested that aqueous oxidation can produce organics with a wide range of volatilities, ranging from volatile to extremely low volatility products [Dennis-Smither et al, 2014;Yu et al, 2014]. For coarse and medium droplet residues, the difference in the O/C ratios due to TD Journal of Geophysical Research: Atmospheres 10.1002/2015JD024508 treatment is insignificant, but for fine droplet residues there is a statistically significant increase (p < 0.03); in the triangle plot (Figure 3b), it is observed that only for fine droplets after TD treatment the point moved to the upper left corner, i.e., f44 increased while f43 decreased (both are statistically significant changes, p < 0.02), which means that in the fine droplet residues, less oxidized organics are also more volatile in nature.…”

Electrodynamic balance–mass spectrometry of single particles as a new platform for atmospheric chemistry research

“…A number of different properties have been studied in this way, including vapor pressures Cotterell et al, 2014;Huisman et al, 2013;Krieger et al, 2017), hygroscopic growth Cotterell et al, 2014;Rovelli et al, 2016), optical properties (Mason et al, 2015), liquid-liquid phase separation , diffusivities and diffusion coefficients (Bastelberger et al, 2017; Published by Copernicus Publications on behalf of the European Geosciences Union. 34 A. W. Birdsall et al: Electrodynamic balance-mass spectrometry of single particles Lienhard et al, 2014), and oxidative aging (Dennis-Smither et al, 2014).…”