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Alastair Lewis  - - - 
Top co-authors See all
Emmanuel Mahieu

183 shared publications

Detlev Helmig

171 shared publications

Elliot Atlas

160 shared publications

Rainer Steinbrecher

59 shared publications

Paul S. Monks

54 shared publications

Publication Record
Distribution of Articles published per year 

Total number of journals
published in
Article 0 Reads 20 Citations Reversal of global atmospheric ethane and propane trends largely due to US oil and natural gas production Detlev Helmig, Samuel Rossabi, Jacques Hueber, Pieter Tans, ... Published: 13 June 2016
Nature Geoscience, doi: 10.1038/ngeo2721
DOI See at publisher website
Article 0 Reads 0 Citations What effect does VOC sampling time have on derived OH reactivity? Hannah Sonderfeld, Iain R. White, Iain C. A. Goodall, James ... Published: 24 May 2016
Atmospheric Chemistry and Physics, doi: 10.5194/acp-16-6303-2016
DOI See at publisher website
ABS Show/hide abstract
State-of-the-art techniques allow for rapid measurements of total OH reactivity. Unknown sinks of OH and oxidation processes in the atmosphere have been attributed to what has been termed “missing” OH reactivity. Often overlooked are the differences in timescales over which the diverse measurement techniques operate. Volatile organic compounds (VOCs) acting as sinks of OH are often measured by gas chromatography (GC) methods which provide low-frequency measurements on a timescale of hours, while sampling times are generally only a few minutes. Here, the effect of the sampling time and thus the contribution of unmeasured VOC variability on OH reactivity is investigated. Measurements of VOC mixing ratios by proton transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS) conducted during two field campaigns (ClearfLo and PARADE) in an urban and a semi-rural environment were used to calculate OH reactivity. VOCs were selected to represent variability for different compound classes. Data were averaged over different time intervals to simulate lower time resolutions and were then compared to the mean hourly OH reactivity. The results show deviations in the range of 1 to 25 %. The observed impact of VOC variability is found to be greater for the semi-rural site.The selected compounds were scaled by the contribution of their compound class to the total OH reactivity from VOCs based on concurrent gas chromatography measurements conducted during the ClearfLo campaign. Prior to being scaled, the variable signal of aromatic compounds results in larger deviations in OH reactivity for short sampling intervals compared to oxygenated VOCs (OVOCs). However, once scaled with their lower share during the ClearfLo campaign, this effect was reduced. No seasonal effect on the OH reactivity distribution across different VOCs was observed at the urban site.
Article 0 Reads 0 Citations A comparison of very short-lived halocarbon (VSLS) and DMS aircraft measurements in the Tropical West Pacific from CAST,... Stephen J. Andrews, Lucy J. Carpenter, Eric C. Apel, Elliot ... Published: 29 April 2016
Atmospheric Measurement Techniques Discussions, doi: 10.5194/amt-2016-94
DOI See at publisher website
ABS Show/hide abstract
We present a comparison of aircraft measurements of halogenated very short-lived substances (VSLS) and dimethyl sulphide (DMS, C2H6S) from a co-ordinated campaign in Jan/Feb 2014 in the Tropical West Pacific. Measurements were made on the NASA Global Hawk, NCAR GV HIAPER and FAAM BAe146 using four separate GC-MS instruments operated by the University of Miami (UoM), the National Centre for Atmospheric Research (NCAR) and two from the University of York (UoY), respectively. The instruments were inter-calibrated during the campaign period using two gas standards on separate scales; a NOAA SX-3581 standard representative of clean low-hydrocarbon air, and an Essex canister prepared by UoM representative of coastal air, which was higher in VSLS and hydrocarbon content. UoY and NCAR use the NOAA scale/standard for VSLS calibration and UoM use a scale based on dilutions of primary standards calibrated by GC with FID and AED (atomic emission) detection. Analysis of the NOAA SX-3581 standard resulted in good agreement for CH2Cl2, CHCl3, CHBr3, CH2Br2, CH2BrCl, CHBrCl2, CHBr2Cl, CH3I CH2ICl and CH2I2 (average RSD < 10 %). Agreement was in general slightly poorer for the UoM Essex canister with an average RSD of < 13 %. Analyses of CHBrCl2 and CHBr3 in this standard however showed significant variability, most likely due to co-eluting contaminant peaks, and a high concentration of CHBr3, respectively. These issues highlight the importance of calibration at atmospherically relevant concentrations (~ 0.5–5 ppt for VSLS). The UoY in-situ GC-MS measurements on-board the BAe146 compare favourably with ambient data from NCAR and UoM, however the UoY whole air samples showed a negative bias for some lower volatility compounds. This systematic bias could be attributed to sample line losses. Considering their large spatial variability, DMS and CH3I displayed good cross-platform agreement without any sampling bias, likely due to their higher volatility. After a correction was performed based upon the UoY in–situ vs whole air data, all four instrument datasets show good agreement across a range of VSLS, with combined mean absolute percentage errors (MAPE) of the four platforms throughout the vertical profiles ranging between 2.2 (CH2Br2) and 15 (CH3I) % across a large geographic area of the Tropical West Pacific. This study shows that the international VSLS calibration scales and instrumental techniques discussed here are in generally good agreement (within ~ 10 % across a range of VSLS), but that losses in aircraft sampling lines can add a major source of uncertainty. Overall, the measurement uncertainty of bromocarbons during these campaigns is much less than the uncertainty in the quantity of VSLS bromine estimated to reach the stratosphere of between 2–8 pptv.
Conference 2 Reads 0 Citations Low-Cost Multispecies Air Quality Sensor Chunting Michelle Wang, Alastair Lewis Published: 08 June 2015
8th Conference of the International Forum on Urbanism (IFoU), doi: 10.3390/ifou-e001
DOI See at publisher website