Abstract
In the present study, time-resolved aerosol particle formation from sulfuric acid vapor is examined with special attention to the stabilization of molecular clusters in the early phase of unary nucleation. An important factor governing this process is the amount of condensable acid vapor. Here it is produced from fast gas-phase reactions in a batch-type reaction cell for which we introduce modifications enabling real-time monitoring. The key component for size- and time-resolved detection of ultrafine particles is a new 1 nm-SMPS. With this new tool at hand, the effect of varying the precursor concentration over two orders of magnitude is investigated. We demonstrate the ability to tune between different growth scenarios as indicated by the size-resolved particle traces which exhibit a transition from sigmoidal over quasi-stationary to peak-like shape. The second key parameter relevant for nucleation studies is the temperature-dependent cluster evaporation. Due to a temperature rise during the mixing stage of the experiment, evaporation is strongly promoted in the early phase. Therefore, the present study extends the T-range used in, e.g., smog chambers. We investigate this temperature effect in a kinetic simulation and can successfully combine simulated and measured data for validating theoretical evaporation rates obtained from DLPNO-CCSD(T0)-calculations.
Highlights
Folkborgsvagen 17, SE-601 76 Norrkoping, Sweden † Electronic supplementary information (ESI) available
It is subsequently transported into the ozone chamber with helium (Linde, Z99.996%) as the carrier gas and the exact amount of O3 is determined by means of UV absorption (lamp: NNI 60/35 XL, absorption path = 37.6 cm, pressure independent absorption coefficient[20] (253.7 nm, 293–298 K) = 298.3 m2 molÀ1, changing less than 1% in this temperature window21)
To further reduce transport time and particle losses, the 1 nm-Scanning Mobility Particle Sizer (SMPS) was operated in a compact design[23] allowing sampling from 1.4 to 30 nm. With this tool at hand, tracking of transient species is realized by two approaches: in the first case, the 1 nm-SMPS is operated at a fixed voltage, providing continuous concentration– time profiles of particles with a defined electrical mobility diameter
Summary
Building on that high supersaturation approach, a kinetic model incorporating molecular gas-phase reactions and particle dynamics was derived. Results from simulations based on this model are compared to particle size distributions (PSDs) measured at the end of each batch indicating a strong. Due to limitations of the previous experimental setup, the particle measurements could not be started directly after gas expansion. Such transient data is an essential target for further validation of the H2SO4 nucleation model. We performed kinetic simulations of PSDs and time profiles, including an explicit treatment of the temperature profile after expansion
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