An Iodide-Adduct High-Resolution Time-of-Flight Chemical-Ionization Mass Spectrometer: Application to Atmospheric Inorganic and Organic Compounds

A high-resolution time-of-flight chemical-ionization mass spectrometer (HR-ToF-CIMS) using Iodide-adducts has been characterized and deployed in several laboratory and field studies to measure a suite of organic and inorganic atmospheric species. The large negative mass defect of Iodide, combined with soft ionization and the high mass-accuracy (<20 ppm) and mass-resolving power (<i>R</i> > 5500) of the time-of-flight mass spectrometer, provides an additional degree of separation and allows for the determination of elemental compositions for the vast majority of detected ions. Laboratory characterization reveals Iodide-adduct ionization generally exhibits increasing sensitivity toward more polar or acidic volatile organic compounds. Simultaneous retrieval of a wide range of mass-to-charge ratios (m/Q from 25 to 625 Th) at a high frequency (>1 Hz) provides a comprehensive view of atmospheric oxidative chemistry, particularly when sampling rapidly evolving plumes from fast moving platforms like an aircraft. We present the sampling protocol, detection limits and observations from the first aircraft deployment for an instrument of this type, which took place aboard the NOAA WP-3D aircraft during the Southeast Nexus (SENEX) 2013 field campaign

Spatial Variation of Aerosol Chemical Composition and Organic Components Identified by Positive Matrix Factorization in the Barcelona Region

The spatial distribution of PM₁ components in the Barcelona metropolitan area was investigated using on-road mobile measurements of atmospheric particle- and gas-phase compounds during the DAURE campaign in March 2009. Positive matrix factorization (PMF) applied to organic aerosol (OA) data yielded 5 factors: hydrocarbon-like OA (HOA), cooking OA (COA), biomass burning OA (BBOA), and low volatility and semivolatile oxygenated OA (LV-OOA and SV-OOA). The area under investigation (∼500 km²) was divided into six zones (city center, harbor, industrial area, precoastal depression, 2 mountain ranges) for measurements and data analysis. Mean zonal OA concentrations are 4.9–9.5 μg m^–3. The area is heavily impacted by local primary emissions (HOA 14–38%, COA 10–18%, BBOA 10–12% of OA); concentrations of traffic-related components, especially black carbon, are biased high due to the on-road nature of the measurements. The formation of secondary OA adds more than half of the OA burden outside the city center (SV-OOA 14–40%, LV-OOA 17–42% of OA). A case study of one measurement drive from the shore to the precoastal mountain range furthest downwind of the city center indicates the importance of nonfossil over anthropogenic secondary OA based on OA/CO

Using Novel Molecular-Level Chemical Composition Observations of High Arctic Organic Aerosol for Predictions of Cloud Condensation Nuclei

Predictions of cloud droplet activation in the late summertime (September) central Arctic Ocean are made using κ-Köhler theory with novel observations of the aerosol chemical composition from a high-resolution time-of-flight chemical ionization mass spectrometer with a filter inlet for gases and aerosols (FIGAERO-CIMS) and an aerosol mass spectrometer (AMS), deployed during the Arctic Ocean 2018 expedition onboard the Swedish icebreaker Oden. We find that the hygroscopicity parameter κ of the total aerosol is 0.39 ± 0.19 (mean ± std). The predicted activation diameter of ∼25 to 130 nm particles is overestimated by 5%, leading to an underestimation of the cloud condensation nuclei (CCN) number concentration by 4–8%. From this, we conclude that the aerosol in the High Arctic late summer is acidic and therefore highly cloud active, with a substantial CCN contribution from Aitken mode particles. Variability in the predicted activation diameter is addressed mainly as a result of uncertainties in the aerosol size distribution measurements. The organic κ was on average 0.13, close to the commonly assumed κ of 0.1, and therefore did not significantly influence the predictions. These conclusions are supported by laboratory experiments of the activation potential of seven organic compounds selected as representative of the measured aerosol

Contribution of Nitrated Phenols to Wood Burning Brown Carbon Light Absorption in Detling, United Kingdom during Winter Time

We show for the first time quantitative online measurements of five nitrated phenol (NP) compounds in ambient air (nitrophenol C₆H₅NO₃, methylnitrophenol C₇H₇NO₃, nitrocatechol C₆H₅NO₄, methylnitrocatechol C₇H₇NO₄, and dinitrophenol C₆H₄N₂O₅) measured with a micro-orifice volatilization impactor (MOVI) high-resolution chemical ionization mass spectrometer in Detling, United Kingdom during January–February, 2012. NPs absorb radiation in the near-ultraviolet (UV) range of the electromagnetic spectrum and thus are potential components of poorly characterized light-absorbing organic matter (“brown carbon”) which can affect the climate and air quality. Total NP concentrations varied between less than 1 and 98 ng m^–3, with a mean value of 20 ng m^–3. We conclude that NPs measured in Detling have a significant contribution from biomass burning with an estimated emission factor of 0.2 ng (ppb CO)⁻¹. Particle light absorption measurements by a seven-wavelength aethalometer in the near-UV (370 nm) and literature values of molecular absorption cross sections are used to estimate the contribution of NP to wood burning brown carbon UV light absorption. We show that these five NPs are potentially important contributors to absorption at 370 nm measured by an aethalometer and account for 4 ± 2% of UV light absorption by brown carbon. They can thus affect atmospheric radiative transfer and photochemistry and with that climate and air quality