1. Molecular and physical characteristics of aerosol at a remote free troposphere site : implications for atmospheric agingSimeon K. Schum, Bo Zhang, Katja Džepina, Paulo Fialho, Claudio Mazzoleni, Lynn R. Mazzoleni, 2018, original scientific article Abstract: Aerosol properties are transformed by atmospheric processes during long-range transport and play a key role in the Earth’s radiative balance. To understand the molecular and physical characteristics of free tropospheric aerosol, we studied samples collected at the Pico Mountain Observatory in the North Atlantic. The observatory is located in the marine free troposphere at 2225m above sea level, on Pico Island in the Azores archipelago. The site is ideal for the study of long-range-transported free tropospheric aerosol with minimal local influence. Three aerosol samples with elevated organic carbon concentrations were selected for detailed analysis. FLEXPART retroplumes indicated that two
of the samples were influenced by North American wildfire
emissions transported in the free troposphere and one by
North American outflow mainly transported within the marine
boundary layer. Ultrahigh-resolution Fourier transform
ion cyclotron resonance mass spectrometry was used to determine
the detailed molecular composition of the samples.
Thousands of molecular formulas were assigned to each of
the individual samples. On average ~60% of the molecular
formulas contained only carbon, hydrogen, and oxygen
atoms (CHO), ~ 30% contained nitrogen (CHNO), and
~ 10% contained sulfur (CHOS). The molecular formula
compositions of the two wildfire-influenced aerosol samples
transported mainly in the free troposphere had relatively low
average O=C ratios (0:48 ± 0:13 and 0:45 ± 0:11) despite the
7–10 days of transport time according to FLEXPART. In contrast,
the molecular composition of the North American outflow
transported mainly in the boundary layer had a higher
average O=C ratio (0:57 ± 0:17) with 3 days of transport time.
To better understand the difference between free tropospheric
transport and boundary layer transport, the meteorological
conditions along the FLEXPART simulated transport pathways
were extracted from the Global Forecast System analysis
for the model grids. We used the extracted meteorological
conditions and the observed molecular chemistry to predict
the relative-humidity-dependent glass transition temperatures
(Tg) of the aerosol components. Comparisons of the
Tg to the ambient temperature indicated that a majority of
the organic aerosol components transported in the free troposphere were more viscous and therefore less susceptible to
oxidation than the organic aerosol components transported
in the boundary layer. Although the number of observations
is limited, the results suggest that biomass burning organic
aerosol injected into the free troposphere is more persistent
than organic aerosol in the boundary layer having broader
implications for aerosol aging. Keywords: secondary organic aerosols, brown carbon, particle dispersion model, ultrahigh-resolution FT-ICR MS, Pico Mountain Observatory Published in RUNG: 10.04.2021; Views: 3245; Downloads: 0 This document has many files! More... |
2. A feasibility study of the use of reactive tracers to determine outdoor daytime OH radical concentrations within the urban environmentIain R. White, Damien Martin, K Fredrik Petersson, Stephen J Henshaw, Graham Nickless, Guy C Lloyd-Jones, Kevin C Clemitshaw, Dudley E Shallcross, 2014, original scientific article Abstract: Using a specifically designed chemical tracer to indirectly measure local atmospheric hydroxyl radical (OH) concentrations is a very appealing concept. Such a tracer will provide information on the amount of OH a tracer encounters, as it moves through the urban environment and provide a stringent test of models. However, to date an outdoor experiment such as this has not been conducted. This article discusses the reasons why this is so and examines the feasibility of using tracers to measure integrated urban OH levels over short (≤1km) distances. Keywords: reactive tracers, OH radicals, NO3 radicals, oxidising rate, dispersion, urban Published in RUNG: 18.07.2019; Views: 3880; Downloads: 0 This document has many files! More... |
3. Tracer concentration profiles measured in central London as part of the REPARTEE campaignDamien Martin, K Fredrik Petersson, Iain R. White, Stephen H Henshaw, Graham Nickless, Amy Lovelock, Janet F Barlow, Tyrone Dunbar, Curtis R Wood, Dudley E. Shallcross, 2011, original scientific article Abstract: There have been relatively few tracer experiments carried out that have looked at vertical plume spread in urban areas. In this paper we present results from two tracer (cyclic perfluorocarbon) experiments carried out in 2006 and 2007 in central London centred on the BT Tower as part of the REPARTEE (Regent's Park and Tower Environmental Experiment) campaign. The height of the tower gives a unique opportunity to study vertical dispersion profiles and transport times in central London. Vertical gradients are contrasted with the relevant Pasquill stability classes. Estimation of lateral advection and vertical mixing times are made and compared with previous measurements. Data are then compared with a simple operational dispersion model and contrasted with data taken in central London as part of the DAPPLE campaign. This correlates dosage with non-dimensionalised distance from source. Such analyses illustrate the feasibility of the use of these empirical correlations over these prescribed distances in central London. Keywords: advection, concentration (composition), dispersion, tracer, urban atmosphere, vertical mixing, vertical profile Published in RUNG: 18.07.2019; Views: 4107; Downloads: 0 This document has many files! More... |
4. Urban tracer dispersion experiments during the second DAPPLE field campaign in London 2004Damien Martin, Catheryn S Price, Iain R. White, Graham Nickless, K Fredrik Petersson, Rex E Britter, Alan G Robins, Stephen E Belcher, Janet F Barlow, Marie Neophytou, Samantha J Arnold, Alan S Tomlin, Robert J Smalley, Dudley E. Shallcross, 2010, original scientific article Abstract: As part of the DAPPLE programme two large scale urban tracer experiments using multiple simultaneous releases of cyclic perfluoroalkanes from fixed location point sources was performed. The receptor concentrations along with relevant meteorological parameters measured are compared with a three screening dispersion models in order to best predict the decay of pollution sources with respect to distance. It is shown here that the simple dispersion models tested here can provide a reasonable upper bound estimate of the maximum concentrations measured with an empirical model derived from field observations and wind tunnel studies providing the best estimate. An indoor receptor was also used to assess indoor concentrations and their pertinence to commonly used evacuation procedures. Keywords: Dapple, dispersion Published in RUNG: 18.07.2019; Views: 3643; Downloads: 0 This document has many files! More... |
5. CityFlux perfluorocarbon tracer experimentsFredrik K Petersson, Damien Martin, Iain R. White, Stephen J Henshaw, Graham Nickless, Ian Longley, Carl J Percival, Martin Gallagher, Dudley E. Shallcross, 2010, original scientific article Abstract: In June 2006, two perfluorocarbon tracer experiments were conducted in central Manchester UK as part of the CityFlux campaign. The main aim was to investigate vertical dispersion in an urban area during convective conditions, but dispersion mechanisms within the street network were also studied. Paired receptors were used in most cases where one receptor was located at ground level and one at roof level. One receptor was located on the roof of Portland Tower which is an 80m high building in central Manchester. Source receptor distances in the two experiments varied between 120 and 600 m. The results reveal that maximum concentration was sometimes found at roof level rather than at ground level implying the effectiveness of convective forces on dispersion. The degree of vertical dispersion was found to be dependent on source receptor distance as well as on building height in proximity to the release site. Evidence of flow channelling in a street canyon was also found. Both a Gaussian profile and a street network model were applied and the results show that the urban topography may lead to highly effective flow channelling which therefore may be a very important dispersion mechanism should the right meteorological conditions prevail. The experimental results from this campaign have also been compared with a simple urban dispersion model that was developed during the DAPPLE framework and show good agreement with this. The results presented here are some of the first published regarding vertical dispersion. More tracer experiments are needed in order to further characterise vertical concentration profiles and their dependence on, for instance, atmospheric stability. The impact of urban topography on pollutant dispersion is important to focus on in future tracer experiments in order to improve performance of models as well as for our understanding of the relationship between air quality and public health. Keywords: air quality, atmospheric chemistry, concentration (composition), convective system, dispersion, public health, street canyon, tracer, urban area Published in RUNG: 18.07.2019; Views: 3799; Downloads: 0 This document has many files! More... |
6. A study of pollutant concentration variability in an urban street under low wind speedsDamien Martin, Catheryn S Price, Iain R. White, Graham Nickless, Adrian Dobre, Dudley E Shallcross, 2008, original scientific article Abstract: The short time‐scale variability in pollutant concentrations in an urban street under very low wind speed conditions and short source–receptor distance has been investigated using the inert tracer sulfur hexafluoride (SF6) as a continuous point‐source (release times ≥ 5 min), and fast detection using separation by gas chromatography coupled with a μ‐electron capture detector (ECD). The results are complex but can be broadly interpreted in terms of horizontal wind speed and direction coherence. Comparisons with a simple dispersion model suggest that observed time‐averaged maximum concentrations approach predicted values, whilst instantaneous maximum concentrations vary greatly and would therefore be difficult to predict. Keywords: dispersion, tracer, intermittency Published in RUNG: 17.07.2019; Views: 3945; Downloads: 133 Full text (289,67 KB) |
7. Solution-Based Fabrication of Carbon Nanotube Bumps for Flip-Chip InterconnectsXu Pingye, Fei Tong, Virginia Davis, Minseo Park, Michael Hamilton, 2014, original scientific article Keywords: Resists, Fabrication, Electrical resistance measurement, Substrates, Dispersion, Resistance, Surface treatment Published in RUNG: 16.01.2017; Views: 4871; Downloads: 0 This document has many files! More... |