Acid–base chemical reaction model for nucleation rates in the polluted atmospheric boundary layer

Abstract

Climate models show that particles formed by nucleation can affect cloud cover and, therefore, the earth's radiation budget. Measurements worldwide show that nucleation rates in the atmospheric boundary layer are positively correlated with concentrations of sulfuric acid vapor. However, current nucleation theories do not correctly predict either the observed nucleation rates or their functional dependence on sulfuric acid concentrations. This paper develops an alternative approach for modeling nucleation rates, based on a sequence of acid-base reactions. The model uses empirical estimates of sulfuric acid evaporation rates obtained from new measurements of neutral molecular clusters. The model predicts that nucleation rates equal the sulfuric acid vapor collision rate times a prefactor that is less than unity and that depends on the concentrations of basic gaseous compounds and preexisting particles. Predicted nucleation rates and their dependence on sulfuric acid vapor concentrations are in reasonable agreement with measurements from Mexico City and Atlanta.amines | atmospheric aerosol | climate forcing | nanoparticle | chamber study N ucleation of atmospheric trace gases occurs regularly throughout the continental boundary layer (1). Nucleated particles grow at typical rates of 1-10 nm/h, and can be a significant source of condensation nuclei (2) and cloud condensation nuclei (CCN) (3). The cloud albedo effect is a major source of uncertainty in estimates of climate radiative forcing (4). Because nucleation may affect CCN concentrations, there is a need for microphysical models that reliably predict atmospheric nucleation rates. Fig. 1 summarizes results for the dependence of boundary layer nucleation rates on the number concentration of sulfuric acid vapor, "[H 2 SO 4 ]," measured by the University of Minnesota-National Center for Atmospheric Research (NCAR) research team over the past two decades (5). Also included are data from the University of Helsinki group (6, 7). The considerable scatter in the measurements of the nucleation rate J at a given value of [H 2 SO 4 ] may be due to factors including dependencies on other nucleation precursor gases, temperature, and relative humidity (RH), as well as uncertainties introduced when J is deduced from measurements. Significantly, Fig. 1 shows that for all of these studies nucleation rates range from 1 × 10 −2 to 5 × 10 −6 times the sulfuric acid vapor collision rate, 0.5k 11 [H 2 SO 4 ] 2 , where k 11 is the hard-sphere collision rate constant for sulfuric acid vapor (8).The literature includes a lively debate about the relative importance of ion-induced and neutral nucleation (9, 10). Our work aims to explain nucleation rates observed in the polluted boundary layer atmospheres of Atlanta and Mexico City, where estimated nucleation rates (∼1-10 3 cm −3 ·s −1 ) were often much greater than typical ion production rates (∼2-30 cm −3 ·s −1 ). Therefore, although ion-induced nucleation could contribute to particle production in these locations it is not the dominant ...

Simplified mechanism for new particle formation from methanesulfonic acid, amines, and water via experiments and ab initio calculations

“…(Indeed, an analogous approach recently applied to atmospheric field measurements was much more successful than traditional analyses for predicting new particle formation from sulfuric acid in air; see ref. 22.) It is noteworthy that our results suggest that rates of new particle formation can be a complex function of not only the nature and concentration of the precursors, including water, but also which precursor specifically is the "limiting reagent."…”

“…This theory has been applied to particle formation in relatively simple systems and clusters of relatively few molecules. Recent data from field and laboratory studies, however, suggest that multicomponent systems with multiple reaction steps are likely involved in new particle formation in the atmosphere (14)(15)(16)(17)(18)(19)(20)(21)(22).…”

Molecular understanding of sulphuric acid–amine particle nucleation in the atmosphere

“…28 in the same flow tube. Another experiment 15 measured high dimer formation rates linked to amine mixing ratios of about 1 part per billion by volume and above. Our results directly link high concentrations of neutral H 2 SO 4 dimer with amines at atmospheric levels.…”

Measurement of neutral sulfuric acid-dimethylamine clusters using CI-APi-TOF-MS

“…Amines have already been predicted as likely candidates enhancing the nucleation rates based on quantum-chemical studies 8,9 and it has been observed that they contribute in the formation of secondary aerosol 10,11 . Laboratory studies as well as atmospheric measurements have also revealed that amines enhance ternary nucleation [12][13][14] . In addition, a recent CLOUD (Cosmics Leaving OUtdoor Droplets) chamber study was able to show that the ternary H 2 SO 4 -H 2 O-DMA (DMA, dimethylamine, (CH 3 ) 2 NH) system can explain atmospheric boundary layer nucleation events for atmospherically relevant concentration of sulfuric acid and dimethylamine under certain conditions 15 .…”