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Abstract
Abstract. Sulfuric acid is known to be a key component for atmospheric nucleation. Precise determination of sulfuric-acid concentration is a crucial factor for prediction of nucleation rates and subsequent growth. In our study, we have noticed a substantial discrepancy between sulfuric-acid monomer concentrations and total-sulfate concentrations measured from the same source of sulfuric-acid vapor. The discrepancy of about 1–2 orders of magnitude was found with similar particle-formation rates. To investigate this discrepancy, and its effect on nucleation, a method of thermally controlled saturator filled with pure sulfuric acid (97% wt.) for production of sulfuric-acid vapor is applied and rigorously tested. The saturator provided an independent vapor-production method, compared to our previous method of the furnace (Brus et al., 2010, 2011), to find out if the discrepancy is caused by the production method itself. The saturator was used in a H2SO4–H2O nucleation experiment, using a laminar flow tube to check reproducibility of the nucleation results with the saturator method, compared to the furnace. Two independent methods of mass spectrometry and online ion chromatography were used for detecting sulfuric-acid or sulfate concentrations. Measured sulfuric-acid or total-sulfate concentrations are compared to theoretical predictions calculated using vapor pressure and a mixing law. The calculated prediction of sulfuric-acid concentrations agrees very well with the measured values when total sulfate is considered. Sulfuric-acid monomer concentration was found to be about 2 orders of magnitude lower than theoretical predictions, but with a temperature dependency similar to the predictions and the results obtained with the ion-chromatograph method. Formation rates are reproducible when compared to our previous results with both sulfuric-acid or total-sulfate detection and sulfuric-acid production methods separately, removing any doubts that the vapor-production method would cause the discrepancy. Possible reasons for the discrepancy are discussed and some suggestions include that the missing sulfuric acid is in clusters, formed with contaminants found in most laboratory experiments. One-to-two-order-of-magnitude higher sulfuric-acid concentrations (measured as total sulfate in this study) would contribute to a higher fraction of particle growth rate than assumed from the measurements by mass spectrometers (i.e. sulfuric-acid monomer). However, the observed growth rates by sulfate-containing vapor in this study does not directly imply a similar situation in the field, where sources of sulfate are much more diverse.
Highlights
Secondary particle formation by gas-to-liquid conversion is widely recognized as an important source of aerosol particles in the atmosphere worldwide (Weber et al, 1996; Kulmala et al, 2004; Spracklen et al, 2006)
Model calculations and observations suggest that new particle formation events with subsequent growth can contribute a substantial amount to cloud condensation nuclei (CCN) concentrations, which can alter the lifetime and albedo of clouds (Lihavainen et al, 2003, 2009; Merikanto et al, 2009)
To quantify the sulfuric acid input for flow-tube nucleation measurements, the saturator output was tested in two experiments: first with chemical ionization mass spectrometer (CIMS) and CI-Atmospheric pressure interface (Api)-TOF and second with MARGA
Summary
Secondary particle formation by gas-to-liquid conversion is widely recognized as an important source of aerosol particles in the atmosphere worldwide (Weber et al, 1996; Kulmala et al, 2004; Spracklen et al, 2006). Benson et al, 2008, 2011; Young et al, 2008; Berndt et al, 2008, 2010; Brus et al, 2010, 2011; Sipilä et al, 2010; Kirkby et al, 2011; Zollner et al, 2012) with different methods of producing the gas-phase sulfuric acid: with their own advantages and disadvantages. The flow-tube measurements with the saturator and the two sulfuric-acid or total-sulfate detection methods were conducted to check reproducibility of particle formation rates between the saturator and the furnace, with similar observed sulfuric-acid or total-sulfate concentrations. The level of ammonia contaminant in the system was determined with the ion-chromatograph method
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