As national air quality networks and international research infrastructures, such as ACTRIS (EU) and ASCENT (US), continue to expand, the deployment of online aerosol chemistry measurements increases worldwide. These research infrastructures are focused on the ability to compare atmospheric properties from one region to another, making it crucial to understand instrument operation in various settings. This paper is part of a series of publications dedicated to better understanding the operation of these instruments using a series of laboratory tests. A particular focus was made on evaluating the organic aerosol (OA) measurement performance of six Aerosol Chemical Speciation Monitors (ACSMs) when sampling known mixtures of organic and inorganic aerosols and in ambient air. The study focuses on assessing the impact of instrument-to-instrument variability on ACSM data processing as well as identifying and quantifying the previously identified m/z44/NO3 artifacts that can affect the accuracy of the measurements. A high degree of variability was observed in instrument measurements of the m/z44/NO3 artifact when compared to results obtained two years earlier (e.g., an increase from similar to 0 in 2016 to 0.16 in 2018 or a decrease from 0.12 in 2016 to 0.05 in 2018), confirming the need for frequent evaluation and quantification during calibration. This study underlines that the product between organic aerosol relative ionization efficiency and the instrument collection efficiency value is instrument dependent and that the variability in these values (1.78 +/- 0.35) should be considered when estimating the measurement uncertainties. Using a range of specific compounds, an average RIEOA for levoglucosan (1.29 +/- 0.23) close to the default value commonly used in ACSM was determined, obtaining a value more specific to each instrument. This study provides valuable information for the calibration and operation of ACSM instruments, ensuring that future studies can build on this work to evaluate and improve instrument performance.

Atmospheric aerosol particles are known to have detrimental effects on human health and climate. Black carbon is an important constituent of atmospheric aerosol particulate matter (PM), emitted from incomplete combustion. Source apportionment of BC is very important, to evaluate the influence of different sources. The high-resolution soot particle aerosol mass spectrometer (HR-SP-AMS) instrument uses a laser vaporiser, which allows the real-time detection and characterisation of refractory black carbon (rBC) and its internally mixed particles such as metals, coating species, and rBC subcomponents in the form of HOA + fullerene. In this case study, the soot data were collected by using HR-SP-AMS during Guy Fawkes Night on 5 November 2014. Positive matrix factorisation was applied to positively discriminate between different wood-burning and bonfire sources for the first time, which no existing black carbon source apportionment technique is currently able to do. Along with this, the use of the fullerene signals in differentiating between soot sources and the use of metals as a tracer for fireworks has also been investigated, which did not significantly contribute to the rBC concentrations. The addition of fullerene signals and successful positive matrix factorisation (PMF) application to HR-SP-AMS data apportioned rBC into more than two sources. These bonfire sources are HOA + fullerene, biomass burning organic aerosol, more oxidised oxygenated organic aerosol (MO-OOA), and non-bonfire sources such as hydrocarbon-like OA and domestic burning. The result of correlation analysis between HR-SP-AMS data and previously published Aethalometer, MAAP, and CIMS data provides an effective way of gaining insights into the relationships between the variables and provide a quantitative estimate of the source contributions to the BC budget during this period. This research study is an important demonstration of using HR-SP-AMS for the purpose of BC source apportionment.

Particulate organonitrates (pON) account for significant fraction of total OA in ambient air. They are formed from the reactions of volatile organic compounds (VOCs) with atmospheric oxidants (OH/NO3 radicals) and NOx. Their quantification can be achieved using aerosol mass spectrometry (AMS), based on the characteristic mass fragment ratio (NO2+/NO+) allowing the distinction from inorganic nitrate. However, the accuracy of the low-resolution aerosol chemical speciation monitor (ACSM) to determine pON has not yet been evaluated. At the Aerosol Chemical Monitor Calibration Centre (ACMCC), an intercomparison for the measurements of pON has been performed in order to obtain a stable and constant generation of pON, so to compare simultaneously the response of nine different AMS/ACSM systems (long-TOF-AMS vs ACSMs; Quads vs TOFs; standard vs capture vaporizers), as well as to investigate the pON physical properties and chemical composition. pON were generated in a Potential Aerosol Mass (PAM) oxidation flow reactor from the reaction of NO3 radical, produced on demand (O3 + NO2), with single VOC precursors. Two biogenic (limonene and b-pinene) and two anthropogenic (acenaphthylene and guaiacol) pON precursors were investigated. For the determination of AMS/ACSM relative ionization efficiencies (RIE), a particle size and mass selection were achieved by combining an aerodynamic aerosol classifier (AAC) and centrifugal a particle mass analyser (CPMA). pON size distribution and total particle number concentration were monitored by a scanning mobility particle sizer (SMPS) and a condensation particle counter (CPC) allowing the characterization of the pON density. In order to get insights into the pON optical properties, as well as their chemical composition and formation processes, measurements also included cavity-enhanced absorption spectroscopy (NO3 radical by IBB-CEAS), proton-transfer-reaction MS (PTR-MS), multi-wavelengths aethalometer (AE33), as well as filter samplings for further high-resolution MS off line analyses (GC and LC/Q-TOF-MS). An overview of the set-up and the experiments performed will be presented together with preliminary key results. This work is part of the European COST Action CA16109 COLOSSAL and the H2020 ACTRIS-2 project (grant agreements n° 654109).

Atmospheric particulate organic nitrates (pON) have recently been shown to account for a large fraction of organic aerosol (OA). Through light absorption, especially at short wavelengths, they make up part of atmospheric brown carbon. While pON might be a non-negligible climate-forcing agent, the physical and optical properties are still poorly documented. As part of the Aerosol Chemical Monitor Calibration Centre (ACMCC) pON experiment, measurements have been conducted to characterize the physical and optical properties of laboratory-generated pON, such as density, mass absorption coefficient (MAC) and refractive index (RI). pON were generated in a Potential Aerosol Mass oxidation flow reactor from the reaction of single VOC precursors with NO3 radical, using two biogenic (limonene and b-pinene) and two anthropogenic (acenaphthylene and guaiacol) compounds. In addition to online physicochemical characterization with aerosol mass spectrometers, a suite of instruments was dedicated to study the physical and optical pON properties, including an aerodynamic aerosol classifier (AAC), a centrifugal particle mass analyzer (CPMA), a scanning mobility particle sizer (SMPS), a condensation particle counter (CPC) and a multi-wavelength aethalometer (AE33). Results will be discussed according to different precursors (biogenic/anthropogenic), as well as compared to the literature data from laboratory experiments for the same (and other) precursors but in different chemical conditions, such as OH or NH3 exposure. Results for laboratory-generated pON will also be compared with ambient air observations.