Sources and sinks driving sulphuric acid concentrations in contrasting environments: implications on proxy calculations

Abstract

Abstract. Sulphuric acid has been shown to be a key driver for new particle formation and subsequent growth in various environments mainly due to its low volatility. However, direct measurements of gas-phase sulphuric acid are oftentimes not available, and the current sulphuric acid proxies cannot predict for example its nighttime concentrations or result in significant discrepancies with measured values. Here, we define the sources and sinks of sulphuric acid in different environments and derive a new physical proxy for sulphuric acid to be utilized in locations and during periods when it is not measured. We used H2SO4 measurements from four different locations: Hyytiälä, Finland; Agia Marina, Cyprus; Budapest, Hungary; and Beijing, China, representing semi-pristine boreal forest, rural environment in the Mediterranean area, urban environment and heavily polluted megacity, respectively. The new proxy takes into account the formation of sulphuric acid from SO2 via OH oxidation and other oxidation pathways, specifically that via stabilized Criegee Intermediates. The sulphuric acid sinks included in the proxy are its condensation sink (CS) and atmospheric clustering starting from H2SO4 dimer formation. Indeed, we found that the observed sulphuric acid concentration can be explained by the proposed sources and sinks with similar coefficients in the four contrasting environments where we have tested it. Thus, the new proxy is a more flexible and an important improvement of previous proxies. Following the recommendations in the manuscript, a proxy for a specific location can be derived.

Decennial time trends and diurnal patterns of particle number concentrations in a Central European city between 2008 and 2018

“…created for clean boreal forest environment. The most recent proxy from Dada et al (2020) is currently under review and has not been tested against the proxy used here. All experimental data were used with their maximum time resolution.…”

Influence of vegetation on occurrence and time distributions of regional new aerosol particle formation and growth

“…Its long-term atmospheric measurements are challenging and, therefore, rare. The H2SO4 concentrations were determined utilising a recently improved calculation method of Dada et al (2020) by adopting the fitted coefficients for Budapest and for radiation intensities >50 W m -2 . The [H2SO4] data obtained were also compared to its proxy derived as [SO2]×GRad/CS (Petäjä et al 2009), which was used previously for many years.…”

Towards understanding the mechanisms of new particle formation in the Eastern Mediterranean

“…Weber et al, 1996;Sipilä et al, 2010). As direct measurements of sulfuric acid is challenging, a suite of proxies for the sulfuric acid concentrations are derived that facilitate calculation of gas phase sulfuric acid from ancillary observations (Dada et al, 2020;Mikkonen et al, 2011;Petäjä et al, 2009;Lu et al, 2019;Weber et al, 1997). In this study, the sulfuric acid proxy was calculated using the new method by Dada et al (2020) for a rural site, which was developed based on observations from the same site of this study : This proxy does not only consider the formation of H2SO4 from SO2 via OH oxidation and the loss towards pre-existing particles (condensation sink), but also includes the formation pathway via stabilized Criegee Intermediates and loss towards atmospheric clustering starting from H2SO4 dimer formation.…”

“…NPF studies over the Mediterranean have focused on the north western basin (Petäjä et al, 2007;Cusack et al, 2013;Berland et al, 2017;Carnerero et al, 2018;Rose et al, 2015;Brines et al, 2015;Hamed et al, 2007;Laaksonen et al, 2005;Casquero-Vera et al, 2020), whereas NPF studies in the eastern basin have been conducted mainly in Greece (Petäjä et al, 2007;Berland et al, 2017;Kalivitis et al, 2015;Kalivitis et al, 2019;Pikridas et al, 2012;Kalkavouras et al, 2019;Kalkavouras et al, 2020;Kopanakis et al, 2013;Siakavaras et al, 2016;Kalkavouras et al, 2017) and very recently in Cyprus (Brilke et al, 2020;Debevec et al, 2018) and Jordan (Hussein et al, 2020). These studies include both short-term campaigns and long-term observation.…”

“…Based on long-term measurements, the annual frequency of NPF over the Mediterranean varies between 10 and 36% (Hussein et al, 2020;Kalivitis et al, 2019;Kalkavouras et al, 2020;Kopanakis et al, 2013). The seasonal cycle has a typical maximum during spring (Kalkavouras et al, 2020;Kopanakis et al, 2013;Kalivitis et al, 2019;Pikridas et al, 2012), even though in some urban background sites the highest frequency was observed during summer (Hussein et al, 2020;Hamed et al, 2007).…”