J. Hopkins

There is growing global consumption of non-fossil fuels such as ethanol made from renewable bioma... more There is growing global consumption of non-fossil fuels such as ethanol made from renewable biomass. Previous studies have shown that one of the main air quality disadvantages of using ethanol blended fuels is a significant increase in the production of acetaldehyde{,} an unregulated and toxic pollutant. Most studies on the impacts of ethanol blended gasoline have been carried out in the US and Brazil{,} with much less focus on the UK and Europe. We report time resolved measurements of ethanol in London during the winter and summer of 2012. In both seasons the mean mixing ratio of ethanol was around 5 ppb{,} with maximum values over 30 ppb{,} making ethanol currently the most abundant VOC in London air. We identify a road transport related source{,} with {'}rush-hour{'} peaks observed. Ethanol is strongly correlated with other road transport-related emissions{,} such as small aromatics and light alkanes{,} and has no relationship to summer biogenic emissions. To determine the impact of road transport-related ethanol emission on secondary species (i.e. acetaldehyde and ozone){,} we use both a chemically detailed box model (incorporating the Master Chemical Mechanism{,} MCM) and a global and nested regional scale chemical transport model (GEOS-Chem){,} on various processing time scales. Using the MCM model{,} only 16% of the modelled acetaldehyde was formed from ethanol oxidation. However{,} the model significantly underpredicts the total levels of acetaldehyde{,} indicating a missing primary emission source{,} that appears to be traffic-related. Further support for a primary emission source comes from the regional scale model simulations{,} where the observed concentrations of ethanol and acetaldehyde can only be reconciled with the inclusion of large primary emissions. Although only constrained by one set of observations{,} the regional modelling suggests a European ethanol source similar in magnitude to that of ethane ([similar]60 Gg per year) and greater than that of acetaldehyde ([similar]10 Gg per year). The increased concentrations of ethanol and acetaldehyde from primary emissions impacts both radical and NOx cycling over Europe{,} resulting in significant regional impacts on NOy speciation and O3 concentrations{,} with potential changes to human exposure to air pollutants.

Papers by J. Hopkins

Isoprene oxidation mechanisms: measurements and modelling of OH and HO<sub>2</sub> over a South-East Asian tropical rainforest during the OP3 field campaign

Atmospheric Chemistry and Physics, 2011

Forests are the dominant source of volatile organic compounds into the atmosphere, with isoprene ... more Forests are the dominant source of volatile organic compounds into the atmosphere, with isoprene being the most significant species. The oxidation chemistry of these compounds is a significant driver of local, regional and global atmospheric composition. Observations made over Borneo during the OP3 project in 2008, together with an observationally constrained box model are used to assess our understanding of this oxidation chemistry. In line with previous work in tropical forests, we find that the standard model based on MCM chemistry significantly underestimates the observed OH concentrations. Geometric mean observed to modelled ratios of OH and HO 2 in airmasses impacted with isoprene are 5.32 +3.68 −4.43 and 1.18 +0.30 −0.30 respectively, with 68 % of the observations being within the specified variation. We implement a variety of mechanistic changes into the model, including epoxide formation and unimolecular decomposition of isoprene peroxy radicals, and assess their impact on the model success. We conclude that none of the current suggestions can simultaneously remove the bias from both OH and HO 2 simulations and believe that detailed laboratory studies are now needed to resolve this issue.

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Quantification and source identification of the Total Elgin gas leak, UK-North Sea, by aircraft sampling

ABSTRACT Aircraft measurement and air sampling have been used to quantify the source and magnitud... more ABSTRACT Aircraft measurement and air sampling have been used to quantify the source and magnitude of the North Sea Total Elgin wellhead platform gas leak in March/April 2012. Isotopic techniques were used to characterise the geological source formation from which the gas came. Initially on 30 March 2012 the leak was in the range 1.6 - 0.7 kg s-1, reducing to less than half that rate by 3 April 2012. Keeling plot analysis of methane in air samples showed that the gas had δ13CCH4 -43‰, implying that the gas source was not the main high-pressure high-temperature Elgin gas field (5.5 km deep, at 190oC) but more probably the overlying Hod Formation. The evidence in the air plume for release of very volatile NMHCs confirmed media reports that the gas leak was on the production platform, above the sea level. This contrasts with the early situation in the BP Deepwater Horizon event, where release was underwater and volatile NMHC species were taken up in the water column. Non-methane hydrocarbons (NMHC) and other volatile organic compounds in the plumes were determined from flask samples by offline analysis. NMHC content was dominated by light alkanes ranging from &gt;20 ppb ethane to &lt;1 ppb benzene and &lt;0.1 ppb higher monoaromatics. The methodology developed in this work is widely applicable to future emissions of environmental concern in circumstances where direct access is difficult or dangerous, and permits unbiased regulatory assessment of potential impact, independent of the emitting party.

Understanding missing OH sinks in a South East Asian tropical rainforest

ABSTRACT Emissions from tropical vegetation account for approximately half of the global source o... more ABSTRACT Emissions from tropical vegetation account for approximately half of the global source of biogenic volatile organic carbon compounds (BVOCs) (Guenther et al. 1995). These BVOCs react rapidly with the hydroxyl radical (OH), and hence play an important role in controlling tropospheric ozone production, aerosol formation and the oxidation capacity in the tropics. Using observations of OH reactivity (Ingham et al., 2009), a direct measure of the total OH sink in an air mass, and supporting observations of a range of BVOCs from within a tropical rainforest in Sabah, Borneo, we investigate the presence of &#39;missing&#39; OH sinks in a carbon rich NOx poor environment. A clear diurnal structure is seen in the OH reactivity measurements, increasing from an average of 7 s-1 just before dawn to an average peak of 32 s-1 in the early afternoon, and correlating with isoprene concentrations (R=0.9). Comparison of these OH reactivity observations with those calculated using a suite of supporting observations of known OH sinks results in underestimation of the average OH reactivity by up to 70%. A series of model sensitivity studies find that unmeasured oxidation products of isoprene can account for this &quot;missing&quot; OH reactivity. The contribution of isoprene oxidation products to the calculated total OH sink is found to be predominantly dependent on the rate of mixing out of the forest canopy and the concentration of OH. With current chemical mechanisms systematically under predicting the OH source strength in these high isoprene low NOx environments, we find that a consequence of the lower calculated OH concentration is a significant underestimate in the calculated OH sink. A constrained box model, containing the near explicit Master Chemical Mechanism chemistry scheme (Jenkin et al. 1997; Saunders et al. 2003) and using observed OH concentrations and a mixing timescale of ~1 day, is able to reproduce the observed OH reactivity without the need for unmeasured primary emitted BVOCs. Guenther, A., et al. A global-model of natural volatile organic compound emissions, J. Geophys. Res., 100, 8873-8892, 1995. Ingham, T., et al. A flow-tube based laser-induced fluorescence instrument to measure OH reactivity in the troposphere, Atmos. Meas. Tech., 2, 465-477, 2009 Jenkin, M. E., et al. The tropospheric degradation of volatile organic compounds: A protocol for mechanism development, Atmos. Environ., 31, 81-104, 1997. Saunders, S. M., et al., Protocol for the development of the master chemical mechanism, MCM v3 (part a): Tropospheric degradation of non-aromatic volatile organic compounds, Atmos. Chem. Phys., 3, 161-180, 2003.

Measurements of nitrogen oxides from Hudson Bay: Implications for NOx release from snow and ice covered surfaces

Atmospheric Environment, 2010

Measurements of NO and NO 2 were made at a surface site (55.28 N, 77.77 W) near Kuujjuarapik, Can... more Measurements of NO and NO 2 were made at a surface site (55.28 N, 77.77 W) near Kuujjuarapik, Canada during February and March 2008. NO x mixing ratios ranged from near zero to 350 pptv with emission from snow believed to be the dominant source. The amount of NO x was observed to be dependent on the terrain over which the airmass has passed before reaching the measurement site. The 24 h average NO x emission rates necessary to reproduce observations were calculated using a zero-dimensional box model giving rates ranging from 6.9 Â 10 8 molecule cm À2 s À1 to 1.2 Â 10 9 molecule cm À2 s À1 for trajectories over land and from 3.8 Â 10 8 molecule cm À2 s À1 to 6.6 Â 10 8 molecule cm À2 s À1 for trajectories over sea ice. These emissions are higher than those suggested by previous studies and indicate the importance of lower latitude snowpack emissions. The difference in emission rate for the two types of snow cover shows the importance of snow depth and underlying surface type for the emission potential of snow-covered areas.

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The characterisation of pollution aerosol in a changing photochemical environment

Atmospheric Chemistry and Physics, 2006

Measurements are presented from a sampling location 50 km downwind of Greater London, UK, to inve... more Measurements are presented from a sampling location 50 km downwind of Greater London, UK, to investigate the timescales required for the atmospheric transformations of aerosol in urban emissions plumes in the context of photochemical age based on the benzene to toluene ratio. It is shown that particles at or around 100 nm in diameter exhibit the greatest systematic variability in chemical properties, and thus hygroscopic properties, on a timescale of 1-2 days. The smaller Aitken mode and larger accumulation mode particles exhibit less variability on these timescales, which we propose is as a result of their different residence times in the atmosphere. The larger accumulation particles have been in the atmosphere longer than the 100 nm particles and their chemistry and hygroscopic properties have been integrated over several days and potentially over several source regions. In contrast, the smaller Aitken mode particles show little systematic variability with photochemical age because their atmospheric lifetimes are short, thus chemical changes and hence changes in water affinity have not had time to occur. Increases in the particle diameter of up to 40% are observed at 90% relative humidity in the accumulation mode from the uptake of water as the particles become increasingly soluble in nature.

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The characterisation of pollution aerosol in a changing photochemical environment

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Quantifying the impact of BOReal forest fires on Tropospheric oxidants over the Atlantic using Aircraft and Satellites (BORTAS) experiment: Design, execution and science overview

by M. Parrington, Andrew Rickard, J. Hopkins, Grant Forster, S. O'Shea, and R. Purvis

Atmospheric Chemistry and Physics, 2013

ABSTRACT We describe the design and execution of the BORTAS (Quantifying the impact of BOReal for... more ABSTRACT We describe the design and execution of the BORTAS (Quantifying the impact of BOReal forest fires on Tropospheric oxidants using Aircraft and Satellites) experiment, which has the overarching objective of understanding the chemical aging of airmasses, containing the emission products from seasonal boreal wildfires, and how they impact downwind atmospheric composition. The central focus of the experiment was a two-week deployment of the UK BAe-146-301 Atmospheric Research Aircraft (ARA) over eastern Canada. This was complemented by ground-based measurements at the Dalhousie University Ground Station (DGS) and the University of Toronto, enhanced ozonesonde launches, measurements on the Pico Mountain Atmospheric Observatory in the Azores, and coordinated space-borne measurements. Integration of these data has helped us to describe pollution plumes from wildfires on a wide spectrum of temporal and spatial scales. These data are interpreted using a range of chemistry models, from a near-explicit gas-phase chemical mechanism to a regional and global model of atmospheric transport and lumped chemistry, and data assimilation tools. We also provide a brief science overview of the project, providing the platform for co-submitted science abstracts.

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Ozone photochemistry in boreal biomass burning plumes

by Andrew Rickard, M. Parrington, and J. Hopkins

Atmospheric Chemistry and Physics, 2013

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An overview of the Amazonian Aerosol Characterization Experiment 2008 (AMAZE-08)

Atmospheric Chemistry and Physics, 2010

The Amazon Basin provides an excellent environment for studying the sources, transformations, and... more The Amazon Basin provides an excellent environment for studying the sources, transformations, and properties of natural aerosol particles and the resulting links between biological processes and climate. With this framework in mind, the Amazonian Aerosol Characterization Experiment (AMAZE-08), carried out from 7 February to 14 March 2008 during the wet season in the central Amazon Basin, sought to understand the

Atmospheric ethanol in London and the potential impacts of future fuel formulations

by Tomás Sherwen and J. Hopkins