Molecular singly charged clusters generated by electrospray sources are commonly used for calibration measurements of ultrafine Condensation Particle Counters (CPCs) in the sub-2 nm size range. This technique has been limited to the smallest singly charged clusters. In this study, we used a bipolar electrospray source combining two electrosprays of opposite polarities to generate singly charged clusters of ammonium salts dissolved in acetonitrile, i.e., tetra-heptyl ammonium bromide (THABr) and tetra-butyl ammonium iodide (TBAI) clusters. A high-resolution UDMA acts as a classifier for positively and negatively charged clusters which are used as mobility standards for the measurement of the complete ascent of the detection efficiency curve of three ultrafine CPCs. The CPCs characterized in this work are two laminar flow-type CPCs using n-butanol (TSI UCPC Model 3776, TSI Inc., Minneapolis, MN USA) and diethylene glycol (DEG) (TSI UCPC Model 3777, TSI Inc.) as working fluid and the turbulent mixing-type DEG-based Particle Size Magnifier (Airmodus A10 PSM). The clusters generated by the bipolar electrospray source are analyzed for their elemental composition using the Atmospheric Pressure interface Time-Of-Flight mass spectrometer (ioniAPi-TOF, Ionicon Analytik GmbH, Austria) in positive and negative ion mode. We present mobility-dependent mass spectra from experiments using the UDMA and the ioniAPi-TOF in series for the analysis of positively charged clusters when operating the electrospray source in unipolar and in bipolar mode to demonstrate the charge reduction and purity of the sample.

Ozone production in the OCU is a function of flowrate and UV light intensity. Figure S1 shows the range of possible ozone concentrations at three different flowrates measured by means of a 205 Dual Beam Ozone Monitor (2B Technologies, USA).Carrier gas was dry, particle-free, synthetic-air (Carbagas ALPHAGAZ 1 quality, Switzerland). Figure S1: OCU ozone production as a function of number of active UV lamps for different flowrates. Error bars represent the 2% precision of the measurement instrument.

Sea spray is a significant global aerosol source with impacts on marine cloud formation and climate. The physical properties and atmospheric fate of the sea spray aerosol (SSA) depend on its chemical composition, but the current understanding of the sources and composition of the marine aerosol or SSA remains limited particularly for the smallest aerosol. The composition of ultrafine (<100 nm diameter) SSA particles controls the critical diameter for activation to cloud droplets. This study presents online measurements of sea salt and organic mass fractions in an ultrafine SSA measured during the Sea Spray Chemistry and Particle Evolution experiment conducted in summer 2019 at the Scripps Institution of Oceanography. Primary SSA particles were generated in a wave flume mesocosm study with coastal seawater obtained from the Scripps Pier in San Diego, CA. Ultrafine particle composition measurements were performed using the thermal desorption chemical ionization mass spectrometer (TDCIMS). Trends in inorganic and organic fractions show dependence on the biological activity of the ocean water, where heterotrophic bacterium concentrations were correlated with organic mass fractions of the ultrafine SSA. At low phytoplankton concentrations, ultrafine sea spray particles were mainly composed of inorganic salts. Characteristic positive ion fragments indicate influence from polysaccharides and fatty acids likely of bacterial origin in the smallest sizes. In contrast, polysaccharide and fatty acid species were below detection levels in TDCIMS measurements of the larger SSA (∼100–200 nm). Comparisons with the submicron aerosol composition measured by an aerosol mass spectrometer (AMS) showed high correlation between AMS and general TDCIMS organic fractions but anticorrelation between measured, individual TDCIMS organics. These results suggest biological drivers for inorganic and organic aerosol compositions and a strong size dependence on the organic composition of nascent sea spray, consistent with previous findings.

Abstract. A significant fraction of atmospheric aerosol particles, which affect both the Earth’s climate and human health, can be attributed to organic compounds and especially secondary organic aerosol (SOA). To better understand the sources and processes generating organic aerosol particles, detailed chemical characterization is necessary, and particles are often collected onto filters and subsequently analyzed by liquid chromatography mass spectrometry (LC-MS). A downside of such offline analysis techniques is the uncertainty regarding artefactual changes in composition occurring during sample collection, storage, extraction and analysis. The goal of this work was to characterize how storage conditions and storage time may affect the chemical composition of SOA generated from β-pinene and naphthalene, as well as from urban atmospheric aerosol samples. SOA samples were produced in the laboratory using an aerosol flow tube and collected on PTFE filters, whereas ambient samples were collected onto quartz filters with a high-volume air sampler. To characterize temporal changes of SOA composition, all samples were extracted and analyzed immediately after collection, but were also stored as aqueous extracts or as filters for 24 hours and up to 4 weeks at three different temperatures of +20 °C, -20 °C or -80 °C, to assess whether a lower storage temperature would be favorable. Analysis was conducted using ultra high-performance liquid chromatography high resolution mass spectrometry (UHPLC-HRMS). Both principal component analysis (PCA) and time series of selected compounds were analyzed to identify the compositional changes over time. We illustrate that the chemical composition of organic aerosols remained stable during low temperature storage conditions, while storage at room temperature led to significant changes over time, even at short storage times of only one day. This indicates that it is necessary to freeze samples immediately after collection, and this requirement is especially important when automated ambient sampling devices are used where filters might be stored in the device for several days before being transferred to a laboratory.

Abstract. We present an electrical mobility classifier for mass–mobility measurements of atmospheric ions. Size segregation coupled with mass spectrometric detection of naturally occurring ions in the atmosphere is challenging due to the low ion concentration. Conventional electrical mobility classifying devices were not yet coupled with mass spectrometry to resolve natural ion composition. This is due to either the insufficient transmission efficiency or design concepts being incompatible with this application, e.g. using high electric fields close to the inlets to push ions from high to low electric potential. Here, we introduce an axial ion mobility classifier, termed AMC, with the aim to achieve higher transmission efficiencies to segregate natural ions at reasonable sizing resolution. Similar to the recently introduced principle of the high-pass electrical mobility filter (HP-EMF) presented by Bezantakos et al. (2015) and Surawski et al. (2017), ions are classified via an electric field that is opposed to the gas flow direction carrying the ions. Compared to the HP-EMF concept, we make use of sheath flows to improve the size resolution in the sub-3 nm range. With our new design we achieve a sizing resolution of 7 Z/ΔZ with a transmission efficiency of about 70 %.