Production and removal of tropospheric oxidants
Halogen oxide kinetics and photochemistry
Iodine species in the atmosphere
Current / recent research
Measurement of Ozone Production Rates
Ozone is a critical air pollutant, harmful to human health, crops and vegetation, an important atmospheric reactant (precursor to the key radical oxidant OH), and a significant greenhouse gas. Understanding atmospheric ozone levels is therefore a key goal for atmospheric chemists, underpinning effective air quality policy measures. As ozone is a secondary pollutant, formed in the atmosphere from the complex processing of NOx and VOCs, predicting ozone levels is still a challenge for atmospheric models. We are developing an alternative approach to this problem, to directly measure the local chemical ozone production rate, as a complementary approach to model (and other observational) tools, and have made preliminary measurements in the UK and India (see news article). This work is funded by NERC and the Royal Society.
Alkene Ozonolysis: Direct and Indirect Radical Production
The gas-phase reaction between ozone and alkenes produces a range of products, including radical species which contribute to atmospheric processing, and partially oxidised organic compounds which add to atmospheric reactivity and aerosol formation. In a series of projects, we have investigated the radical (OH, HO2 and RO2) production from the ozonolysis of a range of alkenes of biogenic and anthropogenic origin, and are now exploring the role of additional ozonolysis products, criegee radicals, as atmospheric oxidants for SO2 and NOx. We use the European Photoreactor (EUPHORE) large simulation chamber facility in Valencia, Spain, as our experimental tool, and interpret the data obtained using the MCM atmospheric model. This work is funded by NERC and the EU EUROCHAMP-2 FP7 programme, and is performed in collaboration with Andrew Rickard & Mat Evans (York), Paul Monks (Leicester) and Marie Camredon (Paris / LISA).
Interactions of Aerosol with Atmospheric Oxidants
Atmospheric oxidants, gas-phase species such as OH and HO2, drive the removal of most pollutants, limit the levels of global warming gases such as methane, and initiate the formation of low-level ozone. They can also react with (chemically age) organic aerosol particles, altering their size, composition hence toxicity and reactivity, a process which can substantially affect both oxidant levels and aerosol characteristics. We are investigating these processes using a laboratory flow-tube system, and aerosol ageing experiments employing an Aerosol Time-of-Flight Mass Spectrometer. This work is being carried out by Suad Al-Kindi, and is performed in collaboration with Roy Harrison.
Point Measurements of Iodine and Bromine in the Marine Boundary Layer
Iodine compounds released from the ocean cause a range of chemical effects in the marine atmosphere - they can influence atmospheric oxidant levels, participate in catalytic ozone destruction cycles and potentially lead to the formation of new atmospheric particles, which may influence cloud formation and hence weather and climate. These natural processes are known to be important in certain coastal regions, but their significance over the open ocean, and hence overall global impact, is uncertain. We have developed a new instrument to measure halogen atoms, using the technique of Resonance Fluorescence, and applied this to measure iodine levels in the North Atlantic, in collaboration with Dwayne Heard (Leeds), and to perform simulation chamber studies of iodine chemistry in collaboration with Cornelius Zetsch (Bayreuth) and Uli Platt (Heidelberg).
Key Publications since 2001
M.S. Alam, A. R. Rickard, M. Camredon, K. P. Wyche, T. Carr, K. E. Hornsby, P. S. Monks & W. J. Bloss (2013) Radical Product Yields from the Ozonolysis of Short Chain Alkenes under Atmospheric Boundary Layer Conditions. J. Phys. Chem. A, 117, 12468-12483
B. Ouyang, M. W. McLeod, R. L. Jones & W. J. Bloss (2013) NO3 radical production from the reaction between the Criegee intermediate CH2OO and NO2, Phys. Chem. Chem. Phys. 15, 17070-17075
R. Sommariva, W.J. Bloss & R. von Glasow (2012) Uncertainties in Gas-Phase Iodine Chemistry, Atmos. Environ. 57, 219-232, 2012.
M. S. Alam, M. Camredon, A. R. Rickard, T. Carr, K. P. Wyche, K. Hornsby, P. S. Monks and W. J. Bloss (2011) Total Radical Yields from Tropospheric Ethene Ozonolysis, Phys. Chem. Chem. Phys., 13, 11002-11015, 2011.
W.J. Bloss, M. Camredon, J. D. Lee, D. E. Heard, J. M. C. Plane, A. Saiz-Lopez, S. J.-B. Bauguitte, R. A. Salmon, and A. E. Jones (2010) Coupling of HOx, NOx and halogen chemistry in the Antarctic boundary layer, Atmos. Chem. Phys., 10, 10187-10209, 2010.
A. K. Mollner, L. Feng, M. K. Sprague, M. Okumura, D. B. Milligan, W. J. Bloss, S. P. Sander, P. T. Martien, R. A. Harley, A. B. McCoy and W.P. Carter (2010) Rate of gas phase association of hydroxyl radical and nitrogen dioxide, Science, 330, 646-649, 2010.
M. Camredon, J. F. Hamilton, M. S. Alam, K. P. Wyche, T. Carr, I. R. White, P. S. Monks, A. R. Rickard, and W. J. Bloss (2010) Distribution of gaseous and particulate organic composition during dark α-pinene ozonolysis, Atmos. Chem. Phys. 10, 2893-2917
C.S.E. Bale, T. Ingham, R. Commane, D.E. Heard and W.J. Bloss (2008) Novel Measurements of atmospheric iodine species by resonance fluorescence, J. Atmos. Chem. 60, 51-70 (2008) Novel Measurements of atmospheric iodine species by resonance fluorescence,. 60, 51-70
W.J. Bloss, J.D. Lee, D.E. Heard, R.A. Salmon, S. J.-B. Bauguitte, H.K. Roscoe and A.E. Jones (2007) Observations of OH and HO2 Radicals in coastal Antarctica. Atmos. Chem. Phys. 7, 4171-4185
W.J. Bloss, M.J. Evans, R. Sommariva, D.E. Heard, M.J. Pilling (2005) The oxidative capacity of the troposphere: Coupling of field measurements of OH and a global chemistry transport model. Faraday Discuss. 130, 425-436.
W.J. Bloss, J.D. Lee, G.P. Johnson, D.E. Heard, R. Sommariva, J.M.C. Plane, A. Saiz-Lopez, G. McFiggans, H. Coe, M. Flynn, P. Williams, A. Rickard and Z. Fleming (2005) Impact of Halogen Monoxide Chemistry upon Boundary Layer OH and HO2 concentrations at a Coastal Site. Geophys. Res. Lett. 32, doi:10.1029/2004GL022084.
W.J. Bloss, S.N. Nickolaisen, R.J. Salawitch, R.R. Friedl and S.P. Sander (2001) Kinetics of the ClO Self-Reaction and 210 nm Absorption Cross Section of the ClO Dimer. J. Phys. Chem. A, 105, 11226-11239.
W.J. Bloss, D.M. Rowley, R.A. Cox and R.L. Jones (2001) Kinetics and Products of the IO Self-Reaction. J. Phys. Chem. A, 105, 7840-7854