Lauriane Lucie Josette Quéléver

Atmospheric new particle formation is driven by condensable vapors such as sulfuric acid and highly oxygenated organic molecules (HOMs). Measuring these gases is challenging because they are present at trace concentrations, they are easily lost through condensation onto surfaces, and they include a large number of chemically diverse species. Chemical Ionization Mass Spectrometry (CIMS) has been extensively used for their detection; however, results obtained in different studies are not always directly comparable. This limitation reflects differences in instrument designs, operating configurations, and reagent ion schemes employed. To investigate these factors, the Aerosol, Clouds and Trace Gases Research Infrastructure (ACTRIS) organized its first CIMS field intercomparison campaign (CI-FI1) during summer 2024 at a Finnish boreal forest site, the SMEAR II (Station for Measuring Forest Ecosystem-Atmosphere Relations) station. Six instruments employing different inlet designs, mass analyzers, and reagent ions were operated using their routine configurations and calibrated according to standard procedures. For sulfuric acid measured in nitrate mode, the conventional sulfuric acid calibration enabled moderately good agreement among instruments, although larger discrepancies were observed at the lower concentrations, typically observed during nighttime. When targeting higher-mass compounds, such as monoterpene-derived HOM monomers (m/z 240–390) and dimers (m/z 480–630), sulfuric acid calibration alone was insufficient to ensure measurement intercomparability and taking into consideration mass-dependent transmission differences proved important to achieve consistent results. Notably, good agreement was observed also for selected compounds measured in bromide mode by different instruments. Overall, the results demonstrate that comparable field measurements of condensable vapors by different CIMS instruments are achievable when all relevant calibration and correction factors are carefully considered. The results further highlight that similarities in instrument behavior are more closely associated with the inlet design and instrument operating conditions than with the reagent ion choice.

Atmospheric new particle formation is driven by condensable vapors such as sulfuric acid and highly oxygenated organic molecules (HOMs). Measuring these gases is challenging because they are present at trace concentrations, they are easily lost through condensation onto surfaces, and they include a wide range of chemically diverse species. Chemical Ionization Mass Spectrometry (CIMS) has been extensively used for their detection; however, results obtained in different studies are not always directly comparable. This limitation reflects differences in instrument designs, operating configurations, and reagent ion schemes employed. To investigate these factors, the Aerosol, Clouds and Trace Gases Research Infrastructure (ACTRIS) organized its first CIMS field intercomparison campaign (CI-FI1) during summer 2024 at a Finnish boreal forest site, the SMEAR II (Station for Measuring Forest Ecosystem-Atmosphere Relations) station. Six instruments employing different inlet designs, mass analyzers, and reagent ions were operated using their routine configurations and calibrated according to standard procedures. For sulfuric acid measured in nitrate mode, the conventional sulfuric acid calibration enabled moderately good agreement among instruments, although larger discrepancies were observed at the lower concentrations, typically observed during nighttime. When targeting higher-mass compounds such as HOM monomers (m/z 240-390) and dimers (m/z 480-630), sulfuric acid calibration alone proved insufficient to ensure measurement intercomparability and taking into consideration mass-dependent transmission differences became important to achieve consistent results. Notably, good agreement was observed also for selected compounds measured in bromide mode by different instruments. Overall, the results demonstrate that comparable field measurements of condensable vapors by different CIMS instruments are achievable when all relevant calibration and correction factors are carefully considered. The results further highlight that similarities in instrument behavior are often more closely associated with the inlet design and instrument operating conditions than with the reagent ion choice.

Atmospheric new particle formation is driven by condensable vapors such as sulfuric acid and highly oxygenated organic molecules (HOMs). Measuring these gases is challenging because they are present at trace concentrations, they are easily lost through condensation onto surfaces, and they include a wide range of chemically diverse species. Chemical Ionization Mass Spectrometry (CIMS) has been extensively used for their detection; however, results obtained in different studies are not always directly comparable. This limitation reflects differences in instrument designs, operating configurations, and reagent ion schemes employed. To investigate these factors, the Aerosol, Clouds and Trace Gases Research Infrastructure (ACTRIS) organized its first CIMS field intercomparison campaign (CI-FI1) during summer 2024 at a Finnish boreal forest site, the SMEAR II (Station for Measuring Forest Ecosystem-Atmosphere Relations) station. Six instruments employing different inlet designs, mass analyzers, and reagent ions were operated using their routine configurations and calibrated according to standard procedures. For sulfuric acid measured in nitrate mode, the conventional sulfuric acid calibration enabled moderately good agreement among instruments, although larger discrepancies were observed at the lower concentrations, typically observed during nighttime. When targeting higher-mass compounds such as HOM monomers (m/z 240-390) and dimers (m/z 480-630), sulfuric acid calibration alone proved insufficient to ensure measurement intercomparability and taking into consideration mass-dependent transmission differences became important to achieve consistent results. Notably, good agreement was observed also for selected compounds measured in bromide mode by different instruments. Overall, the results demonstrate that comparable field measurements of condensable vapors by different CIMS instruments are achievable when all relevant calibration and correction factors are carefully considered. The results further highlight that similarities in instrument behavior are often more closely associated with the inlet design and instrument operating conditions than with the reagent ion choice.

Atmospheric new particle formation is driven by condensable vapors such as sulfuric acid and highly oxygenated organic molecules (HOMs). Measuring these gases is challenging because they are present at trace concentrations, they are easily lost through condensation onto surfaces, and they include a wide range of chemically diverse species. Chemical Ionization Mass Spectrometry (CIMS) has been extensively used for their detection; however, results obtained in different studies are not always directly comparable. This limitation reflects differences in instrument designs, operating configurations, and reagent ion schemes employed. To investigate these factors, the Aerosol, Clouds and Trace Gases Research Infrastructure (ACTRIS) organized its first CIMS field intercomparison campaign (CI-FI1) during summer 2024 at a Finnish boreal forest site, the SMEAR II (Station for Measuring Forest Ecosystem-Atmosphere Relations) station. Six instruments employing different inlet designs, mass analyzers, and reagent ions were operated using their routine configurations and calibrated according to standard procedures. For sulfuric acid measured in nitrate mode, the conventional sulfuric acid calibration enabled moderately good agreement among instruments, although larger discrepancies were observed at the lower concentrations, typically observed during nighttime. When targeting higher-mass compounds such as HOM monomers (m/z 240-390) and dimers (m/z 480-630), sulfuric acid calibration alone proved insufficient to ensure measurement intercomparability and taking into consideration mass-dependent transmission differences became important to achieve consistent results. Notably, good agreement was observed also for selected compounds measured in bromide mode by different instruments. Overall, the results demonstrate that comparable field measurements of condensable vapors by different CIMS instruments are achievable when all relevant calibration and correction factors are carefully considered. The results further highlight that similarities in instrument behavior are often more closely associated with the inlet design and instrument operating conditions than with the reagent ion choice.

Inclusion of methanethiol (MeSH) in global atmospheric chemistry–climate model assessments has shown that MeSH emissions increase SO ₂ , particulate sulfate and aerosol cooling over the Southern Ocean. However, measurements in the Southern Ocean are sparse. In February and March 2023, we deployed three online high-resolution mass spectrometers to measure MeSH and dimethyl sulfide (DMS) in seawater (down to 100 m in depth) and air during a cruise on the west side of the Antarctic Peninsula and in the Weddell Sea. MeSH concentrations in surface seawater (mean 0.5, range 0.11 to 1.7 nmol dm ⁻³ ) were within the range previously reported for polar and subpolar regions. Considering concurrent DMS seawater concentrations (mean 1.6, range 0.45 to 11.3 nmol dm ⁻³ ), MeSH represented 28±8 % of the ocean's volatile methylated sulfur (VMS = DMS + MeSH). Depth profiles of MeSH showed higher concentrations in the euphotic layer. Sea to air fluxes of MeSH (mean 0.9, range 0.03 to 4.3 µmol m ² d ⁻¹ ) were comparable to those of DMS (mean 1.7, range −0.6 to 8.6 µmol m ² d ⁻¹ ). Ambient air MeSH (mean 0.015, range 0.001 to 0.060 ppbv) was low and similar to other observations. Air DMS concentrations were about a factor of 10 higher than MeSH (mean 0.25, range 0.008 to 1.35 ppbv) and there was excellent agreement between two different instruments using different ionization chemistries. MeSH seawater concentrations, sea–air fluxes, and atmospheric mixing ratios displayed depletion during daytime. Overall, this dataset represents a useful resource for model integration and validation.

Atmospheric new particle formation is driven by condensable vapors such as sulfuric acid and highly oxygenated organic molecules (HOMs). Measuring these gases is challenging because they are present at trace concentrations, they are easily lost through condensation onto surfaces, and they include a wide range of chemically diverse species. Chemical Ionization Mass Spectrometry (CIMS) has been extensively used for their detection; however, results obtained in different studies are not always directly comparable. This limitation reflects differences in instrument designs, operating configurations, and reagent ion schemes employed. To investigate these factors, the Aerosol, Clouds and Trace Gases Research Infrastructure (ACTRIS) organized its first CIMS field intercomparison campaign (CI-FI1) during summer 2024 at a Finnish boreal forest site, the SMEAR II (Station for Measuring Forest Ecosystem-Atmosphere Relations) station. Six instruments employing different inlet designs, mass analyzers, and reagent ions were operated using their routine configurations and calibrated according to standard procedures. For sulfuric acid measured in nitrate mode, the conventional sulfuric acid calibration enabled moderately good agreement among instruments, although larger discrepancies were observed at the lower concentrations, typically observed during nighttime. When targeting higher-mass compounds such as HOM monomers (m/z 240-390) and dimers (m/z 480-630), sulfuric acid calibration alone proved insufficient to ensure measurement intercomparability and taking into consideration mass-dependent transmission differences became important to achieve consistent results. Notably, good agreement was observed also for selected compounds measured in bromide mode by different instruments. Overall, the results demonstrate that comparable field measurements of condensable vapors by different CIMS instruments are achievable when all relevant calibration and correction factors are carefully considered. The results further highlight that similarities in instrument behavior are often more closely associated with the inlet design and instrument operating conditions than with the reagent ion choice.

Atmospheric new particle formation is driven by condensable vapors such as sulfuric acid and highly oxygenated organic molecules (HOMs). Measuring these gases is challenging because they are present at trace concentrations, they are easily lost through condensation onto surfaces, and they include a wide range of chemically diverse species. Chemical Ionization Mass Spectrometry (CIMS) has been extensively used for their detection; however, results obtained in different studies are not always directly comparable. This limitation reflects differences in instrument designs, operating configurations, and reagent ion schemes employed. To investigate these factors, the Aerosol, Clouds and Trace Gases Research Infrastructure (ACTRIS) organized its first CIMS field intercomparison campaign (CI-FI1) during summer 2024 at a Finnish boreal forest site, the SMEAR II (Station for Measuring Forest Ecosystem-Atmosphere Relations) station. Six instruments employing different inlet designs, mass analyzers, and reagent ions were operated using their routine configurations and calibrated according to standard procedures. For sulfuric acid measured in nitrate mode, the conventional sulfuric acid calibration enabled moderately good agreement among instruments, although larger discrepancies were observed at the lower concentrations, typically observed during nighttime. When targeting higher-mass compounds such as HOM monomers (m/z 240-390) and dimers (m/z 480-630), sulfuric acid calibration alone proved insufficient to ensure measurement intercomparability and taking into consideration mass-dependent transmission differences became important to achieve consistent results. Notably, good agreement was observed also for selected compounds measured in bromide mode by different instruments. Overall, the results demonstrate that comparable field measurements of condensable vapors by different CIMS instruments are achievable when all relevant calibration and correction factors are carefully considered. The results further highlight that similarities in instrument behavior are often more closely associated with the inlet design and instrument operating conditions than with the reagent ion choice.

Laboratory experiments addressing complex phenomena such as atmospheric new-particle formation and growth typically involve numerous instruments measuring a range of key coupled variables. In addition to independent calibration, the combined dataset provides not just constraints on the parameters of interest but also on the critical instrument calibrations. Here we find good agreement between production and loss rates of sulfuric acid (H₂SO₄) in an experiment performed at the CERN CLOUD chamber involving oxidation of sulfur dioxide (SO₂) in the presence of ammonia (NH₃) at 58 % relative humidity, driving new-particle formation and growth of particles by H₂SO₄+NH₃ nucleation initiated by O₃ photolysis via several light sources. This closure requires consistency across numerous parameters, including: the particle number and size distribution; their condensation sink for H₂SO₄; the particle growth rates; the concentration of H₂SO₄; and the nucleation coefficients for both neutral and ion-induced pathways. Our study shows that accurate agreement can be achieved between production and loss of condensable vapors in laboratory chambers under atmospheric conditions, with accuracy ultimately tied to particle number measurement (i.e. a condensation particle counter). This, in turn implies parameters such as the H₂SO₄ concentration and particle size distributions can be determined to a comparable precision.

Inclusion of methanethiol (MeSH) in global chemistry–climate models has shown that MeSH emissions increase SO₂, particulate sulfate and aerosol cooling over the Southern Ocean. However, measurements in the Southern Ocean are sparse. In February and March 2023, we deployed three online high-resolution mass spectrometers to measure MeSH and dimethyl sulfide (DMS) in seawater (down to 100 m in depth) and air during a cruise on the west side of the Antarctic Peninsula and the Weddell Sea. MeSH concentrations in surface seawater (mean 0.56, range 0.12 to 1.9 nmol dm^-3) were within the range previously reported for the polar and subpolar regions. Considering concurrent DMS concentrations (mean 1.6, range 0.45 to 11.3 nmol dm^-3), MeSH represented 30 ± 7 % of the ocean’s volatile methylated sulfur (VMS = DMS + MeSH). Depth profiles of MeSH showed higher concentrations in the euphotic layer. Sea to air fluxes of MeSH (mean 1.0, range 0 to 5.0 µmol m² d^-1) were comparable to those of DMS (mean 1.7, range -0.6 to 8.6 µmol m² d^-1). Ambient air MeSH (mean 15, range 1 to 60 pptv) was low and similar to other observations. Air DMS concentrations were about a factor of 10 higher than MeSH (mean 0.25, range 0.01 to 1.35 ppb) and there was excellent agreement between two different mass spectrometer instruments using different ionization chemistry. MeSH seawater concentrations, sea–air fluxes, and atmospheric mixing ratios displayed depletion during daytime. Overall, this dataset represents a useful resource for model validation.