Principle Investigator: Jon Abbatt

Year Awarded: 2016

Institution: University of Toronto

The overall goal of this project is to assess the multiphase chemistry that occurs on indoor surfaces and aerosol particles, with three general areas of focus:

  • Oxidation chemistry of organic material, such as skin and cooking oils
  • Chemistry of indoor combustion emissions, such as PAHs, cigarette smoke and HONO
  • Chemistry of cleaning materials, such as chlorine bleach

These projects were spawned from preliminary studies conducted during an initial two-year grant from the Sloan Foundation. As well, some of these projects described below have been extended through our participation in the HOMEChem campaign in summer 2018.

  1. Oxidation chemistry of organic material, such as skin and cooking oils

Ozone is an important indoor oxidant, especially on surfaces. Whereas ozone loss kinetics (deposition velocities) have been measured on a wide variety of surfaces, the products are complex and not well characterized. Our group uses a variety of analytical techniques to study organic surface oxidation, with a focus on the unsaturated molecules that are major components of skin and cooking oils. We see evidence for Criegee intermediate reactions, which can lead to the loss of saturated acids (even perfluorinated acids!). A novel observation is the formation of stable secondary ozonides, for example in the oxidation of triolein which is a major component of olive oil. Below is a DART-MS spectrum illustrating the change in composition when skin oil is oxidized:

Slow oxidation of organic films may also occur via OH heterogeneous oxidation. This chemistry is likely only relevant for very low volatility substances that are not reactive with other oxidants. For example, palmitic acid is a long-chain fatty acid that will arise from skin oils, and phthalates are common indoor pollutants that are widely used as plasticizers. We have shown that OH heterogeneous oxidation will lead to lifetimes of weeks to months for species adsorbed on indoor surfaces as (roughly) nm-thick films. We are collaborating with G. Morrison and M. Shiraiwa on developing a numerical model that quantitatively describes the mass transfer of such reactive species to wall surfaces.

Experimentally, this work has required the development of new analytical methods for the study of organic heterogeneous chemistry. We have published two papers on this topic, for the application of DART-MS and the identification of organic hydroperoxides.

  1. Chemistry of indoor combustion emissions, such as PAHs, cigarette smoke and HONO

Combustion is a messy activity, with many products of incomplete burning arising. This occurs indoors via gas stoves, smoking, candle-burning, incense burning, etc. One aspect of our research involves the measurement of the oxidation kinetics and products of ozone interacting with surface-deposited PAHs, important products of incomplete combustion. The kinetics are complex, driven by phase separation, formation of unreactive crusts on the substrate surface, and slow diffusion. In collaboration with Manabu Shiraiwa, we are decoupling these processes to gain a comprehensive view of the overall multiphase process. As well, we have experimentally shown that PAH/soot oxidation drives: i) the formation of long-lived radicals in the substrates, ii) increased redox cycling abilities, and iii) formation of highly carcinogenic species, such as benzo[a]pyrene diol epoxide. This molecule was previously thought to only form biotically, but we have shown that such PAH diol epoxides form via heterogeneous oxidation under indoor conditions.

Another aspect of our research has involved a residence study where we characterized the particulate and gaseous emissions from a gas stove, research cigarette and a candle. Jeff Siegel’s group is analyzing the ultrafine particle emissions. Ours has focussed largely on the gaseous species detected, including HONO which is apparently semi-volatile with evidence for desorption from surfaces after house flushing. These surface emissions are in addition to primary emissions from stoves, etc. We have extended these observations of semi-volatile behavior for small molecules during the HOMEChem campaign in Austin TX.

Finally, we have explored the primary and secondary processes associated with second-hand cigarette smoke. In a small Teflon chamber we have oxidized second-hand smoke and observed the formation of ultrafine particles with ozone exposure (see below) and HNCO formation with OH exposure. In the same chamber, after it has been exposed to second hand smoke but then flushed, we have quantified how different seed aerosol give rise to third-hand smoke aerosol particles.

  1. Chemistry of cleaning materials, such as chlorine bleach

High mixing ratios of both gaseous HOCl and Cl2 are observed in the gas phase upon floor washing. HOCl decays away faster than the air exchange rate, indicative of a surface reaction. Numerous other chlorinated species are observed – e.g. NHCl2, NCl3, ClNO2 and particulate chlorine. Photochemical modeling conducted by Nic Carslaw indicates that significant levels of Cl and OH radicals may form photochemically. The overall conclusions are that bleach washing oxidizes not only the wetted surface but potentially also other surfaces (through gas phase HOCl uptake) and the gas phase (through OH and Cl production).

To investigate the surface uptake of HOCl, we have used DART-MS and FTIR-ATR analysis to examine reaction with squalene and oleic acid, i.e. components of skin oil and cooking oil. HOCl uptake is rapid, leading to chlorination of the starting materials. To give a sense of timescales, with roughly 1 hour of exposure to 600 ppmv of HOCl, three to four chlorine atoms become covalently incorporated into the squalene molecule via the chlorohydrin reaction. For reference, 250 ppbv of HOCl was measured in a very-well ventilated laboratory via floor washing and we expect much higher mixing ratios will prevail in less-well ventilated spaces. We conclude that components of our skin oils likely get chlorinated with bleach washing, and may be the cause of some people’s allergic response to this cleaning agent. Below is a DART-MS spectrum of a squalene (MW = 410) surface exposed to 600 ppbv HOCl:

Personnel

  • Ramina Alwarda (MSc 2017)
  • Nadine Borduas (PhD, 2015; currently postdoc at ETH-Zurich)
  • Cuyler Borrowman (MSc 2016; currently PhD student at Monash University)
  • Doug Collins (postdoc; currently Assistant Professor at Bucknell University)
  • Rachel Hems (currently PhD student)
  • Heather Schwartz-Narbonne (BSc 2017; currently MSc student)
  • Jennifer Faust (postdoc; currently Assistant Professor at College of Wooster)
  • Chen Wang (currently postdoc)
  • Zilin Zhou (currently PhD student)
  • Shouming Zhou (currently research associate)

Publications

  1. Antiñolo, M.D. Willis, S. Zhou, J.P.D. Abbatt. Connecting the oxidation of soot to its redox cycling abilities. Nature Communications, 6, 6812-6815 (2015).
  2. Zhou, M. W. Forbes, J. P. D. Abbatt, Application of direct analysis in real time-mass spectrometry (DART-MS) to the study of gas-surface heterogeneous reactions: focus on ozone and PAHs. Anal. Chem.,87, 4733–4740, (2015).
  3. Borduas, J.G. Murphy, C. Wang, G. da Silva, J.P.D. Abbatt, Gas Phase Oxidation of Nicotine by OH Radicals: Kinetics, Mechanisms, and Formation of HNCO, Environmental Science and Technology Letter, 3,327-331 (2016).
  4. Zhou, M.W. Forbes, Y. Katrib, J. Abbatt. Rapid oxidation of skin oil by ozone. Environmental Science and Technology Letters, 3, 170-174 (2016).
  5. S. Zhou, M.W. Forbes, J.P.D. Abbatt, Kinetics and Products from Heterogeneous Oxidation of Squalene with Ozone. Environmental Science and Technology, 50, 11688-11697 (2016).
  6. Borrowman, S. Zhou, T.E. Burrow, J.P.D. Abbatt, Formation of environmentally persistent free radicals from the heterogeneous reaction of ozone and polycyclic aromatic compounds, Phys. Chem. Chem. Phys., 18, 205-212 (2016).
  7. J. P. S. Wong, N. Carslaw, R. Zhao, S. Zhou, J. P. D. Abbatt, Observations and impacts of bleach washing on indoor chlorine chemistry, Indoor Air, 27, 1082-1090 (2017).
  8. S.M. Zhou, L.W.Y. Yeung, M.W. Forbes, S. Mabury, J.P.D. Abbatt, Epoxide formation from heterogeneous oxidation of benzo[a] pyrene with gas-phase ozone and indoor air, Environmental Science: Processes and Impacts, 19, 1292-1299 (2017).
  9. C. Wang, D.B. Collins, R.F. Hems, N. Borduas, M. Antinolo, J.P.D. Abbatt, Exploring Conditions for Ultrafine Particle Formation from Oxidation of Cigarette Smoke in Indoor Environments, Environmental Science and Technology, 52, 4623-4631 (2018).
  10. S. Zhou, Identification of Organic Hydroperoxides and Peroxy Acids Using Atmospheric Pressure Chemical Ionization – Tandem Mass Spectrometry (APCI-MS/MS): Application to Secondary Organic Aerosol, Atmospheric Measurement Techniques, 11, 3081-3089 (2018).
  11. R. Alwarda, S. Zhou, J.P.D. Abbatt, Heterogeneous Oxidation of Indoor Surfaces by Gas-Phase Hydroxyl Radicals, Indoor Air, in press, DOI: 10.1111/ina.12476 (2018).
  12. S. Zhou, S. Joudan, M.W. Forbes, J.P.D. Abbatt, Reaction of Criegee Intermediates with Organic Acids in the Condensed Phase, Environmental Science and Technology Letters, submitted, 2018.
  13. D.B. Collins, R.F. Hems, S. Zhou, M. Alavy, J.A. Siegel, J.P.D. Abbatt, Evidence for Gas-Surface Equilibrium Control of Indoor Nitrous Acid, Environmental Science and Technology, submitted, 2018.
  14. Schwartz-Narbonne, C. Wang, S. Zhou, J.P.D. Abbatt, J. Faust, Heterogeneous chlorination of squalene and oleic acid, Heterogeneous chlorination of squalene and oleic acid, Environmental Science and Technology, submitted, 2018.
  15. B. Collins, C. Wang, J.P.D. Abbatt, Selective Uptake of Third Hand Tobacco Smoke Components to Inorganic and Organic Aerosol Particles, Environmental Science and Technology, submitted, 2018.

Collaborators

  • Prof. N. Carslaw, University of York
  • Prof. G. Morrison, U North Carolina
  • Prof. M. Shiraiwa, UC Irvine
  • Prof. J. Siegel, University of Toronto