Aging aerosol in a well-mixed continuous-flow tank reactor: an introduction of the activation time distribution

Abstract

Abstract. Two approaches are commonly used to simulate atmospheric aging processes in the laboratory. The experiments are either performed in large aerosol chambers (several m3) in order to achieve extended observation times or in small chambers (< 1 m3), compensating for the short observation times by elevated reactant concentrations. We present an experimental approach that enables long observation times at atmospherically relevant reactant concentrations in small chamber volumes by operating the aerosol chamber as a continuous-flow stirred tank reactor (CSTR). We developed a mathematical framework that allows the retrieval of data beyond calculating mean values, such as O3 exposure or equivalent atmospheric aging time, using the new metric, activation time (tact). This concept was developed and successfully tested to characterize the change in cloud condensation nuclei (CCN) activity of soot particles due to heterogeneous ozone oxidation. We found very good agreement between the experimental results and the theoretical predictions. This experimental approach and data analysis concept can be applied for the investigation of any transition in aerosol particles properties that can be considered a binary system. Furthermore, we show how tact can be applied to the analysis of data originating from other reactor types such as oxidation flow reactors (OFRs), which are widely used in atmospheric sciences. The new tact concept significantly supports the understanding of data acquired in OFRs, especially those from deviating experimental results in intercomparison campaigns.

Ozone Concentration versus Temperature: Atmospheric Aging of Soot Particles

“…The sample investigated by the instruments downstream of the chamber does not consist of homogeneously aged aerosol particles but of a well-defined mix of particles at different individual aging stages. The ratio between young, medium-aged, and old particles is defined by the particle age distribution (PAD) . The PAD can be obtained from the residence time distribution (RTD) taking particle losses into account (see the work of Friebel et al for more details).…”

“…t act can be calculated directly from the measured AF during steady state using eq . A full derivation of eq and how AF and t act correlate if the aerosol chamber is not in steady state can be found in Friebel and Mensah …”

“…Further, low particle number concentrations (<1000/cm 3 ) are sufficient, which allows for size selection of the particles prior to the aging step. Though not as popular as OFRs or batch reactors, this concept has been used previously in atmospheric sciences for the investigation of, e.g., SOA formation , and gas phase chemistry, but was only recently adopted for the investigation of CCN activation …”

Measuring the Chemical Evolution of Levitated Particles: A Study on the Evaporation of Multicomponent Organic Aerosol

“…Laboratory-based techniques have long been employed to explore the formation and evolving composition of aerosol under atmospheric conditions. Environmental chambers, tank reactors, and flow tubes have been effectively coupled with various advanced analytical methods to characterize size distributions and chemical composition in aerosol particle ensembles. − Mass spectrometry (MS) methods are most commonly adopted to yield composition data using a variety of ionization methods and MS configurations. − While electron impact ionization is commonly used in aerosol MS, − atmospheric pressure ionization methods using electrospray and plasma discharge ionization are becoming more common, providing increased molecular details. − These ensemble methods can provide detailed insights into reaction pathways and kinetics and allow for improved predictions of aerosol composition in climate models. − Characterizing the physical properties of aerosol can be more challenging, requiring specialized experimental platforms to probe volatility, hygroscopicity, optical properties, and so forth. − Other physical properties, such as particle viscosity, surface tension, and phase morphology, cannot be easily probed using ensemble methods.…”

Evolution dynamics of fractal aggregates in continuously stirred tank aerosol reactors using generalized condensation exponents

“…Among different types of reactors, Continuously Stirred Tank Aerosol Reactor (CSTAR) is a homogeneous, isothermal, constant volume tank, in which particles are formed from the nucleation of a vapor maintained under constant flow. This system is used for the production of particles at industrial scale (Pratsinis 1998) and to study aerosol formation processes by nucleation of reactant gases/vapors under constant flow conditions (Adkins et al 1988;Friebel and Mensah 2019;Kuwata and Martin 2012;McMurry and Li 2017). Subsequent to nucleation, the particles further grow in size due to either vapor condensation or coagulation, and are removed from the system either by outflow or by deposition on walls of the reactor.…”