Ozone Concentration versus Temperature: Atmospheric Aging of Soot Particles

Abstract

The oxidation of soot particles with ozone (O 3 ) increases the particles' ability to act as cloud condensation nuclei (CCN). To assess if this process is a relevant source for CCN in the atmosphere, the reaction rate at atmospheric conditions must be known. Here we investigate the increase in CCN activity of soot particles rich in organic carbon at O 3 concentrations ranging from 0−200 ppb and between 5 and 35 °C. We operated an ∼3 m 3 aerosol chamber as a continuous-flow stirred tank reactor which allows for aging times of up to 12 h and beyond and of particle size selection prior to the aging step. We applied the activation time (t act ) concept to retrieve kinetic data. It was found that 100 nm soot particles can be CCN-active down to supersaturations of 0.3% after 12 h of exposure to 200 ppb O 3 at 35 °C. The reaction rate was found to be not directly proportional to the O 3 concentration. Instead, a Langmuir-type reaction kinetic was found to be the best fit to parametrize the reaction rates. The initial reaction step is therefore the adsorption of O 3 molecules, which could be detected by an increase in the particle diameter of up to 3.7 nm within several minutes after exposure. The increase in particle diameter agrees well with the calculated change in the O 3 surface coverage, which was obtained from CCN activation data under the assumption of a Langmuir-sorption isotherm. Further, we found that a temperature increase from 5 to 35 °C increases the reaction rate by a factor of 5 which corresponds to an activation energy of 38.5 kJ•mol −1 . Extrapolation to atmospheric conditions allows for the conclusion that the temperature is as important as the O 3 concentration for the CCN activation of soot particles within the atmospheric range.

Aging induced changes in ice nucleation activity of combustion aerosol as determined by near edge X-ray absorption fine structure (NEXAFS) spectroscopy

“…While freshly emitted soot particles are usually hydrophobic, 9 both the physical and chemical properties of the soot particles can be altered during atmospheric aging. 10 The breadth of atmospheric aging covers a large variety of processes, including oxidation by atmospheric trace gases, 11 photochemical reactions 12 as well as condensation (coating) of semi-volatile material such as secondary organic aerosol (SOA) species 13 and sulfuric acid (H 2 SO 4 ) on the soot particles, 14 changing the mixing state of the aerosol particles 15 and in turn their radiative properties. 16,17 Some studies have investigated the various consequences of atmospheric aging of soot particles for their susceptibility to interact with atmospheric water and their ability to serve as nucleation sites for water vapor, which is critical to quantify their cloud formation potential.…”

Ionic Strength Effect Alters the Heterogeneous Ozone Oxidation of Methoxyphenols in Going from Cloud Droplets to Aerosol Deliquescent Particles

“…The uptake coefficients in dilute aqueous phase are slightly enhanced, from γ = (1.7 ± 0.1) × 10 –7 at 278.15 K to γ = (4.1 ± 0.1) × 10 –7 at 318.15 K (see Figure S3). The obtained results seem to be consistent with those of a previous study focused on the heterogeneous reaction of O 3 with methoxyphenols. , The activation energy E A of the heterogeneous reaction between O 3 and ACS was estimated by applying the Arrhenius law to the data reported in Figure .…”

“…The obtained results seem to be consistent with those of a previous study focused on the heterogeneous reaction of O 3 with methoxyphenols. 15,62 The activation energy E A of the heterogeneous reaction between O 3 and ACS was estimated by applying the Arrhenius law to the data reported in Figure 5.…”

Weakened Haze Mitigation Induced by Enhanced Aging of Black Carbon in China

“…Due to poor hygroscopicity, the initial aging of fresh BC is dominated by photochemical oxidation . When fresh BC is under relatively high O 3 conditions, the initial aging by strong photochemical oxidation will significantly increase the contribution of inorganic components with good hygroscopicity to BC coating materials (e.g., nitrates shown in Figure e); on the other hand, the primary organic aerosols associated with fresh BC can be oxidized by heterogeneous ozonization reactions (i.e., BC-initiated gas–particle interactions), which will boost the hygroscopicity of organic coating materials. − This implies that the BC-containing particles suffering stronger photochemistry more easily underwent aqueous and heterogeneous (i.e., gas–aerosol water) reactions during haze pollution in 2018 than those in 2014. As demonstrated by Figure a,c, under a haze pollution environment, a lower RH was needed in 2018 than in 2014 to reach the same BC aging degree.…”