S. G. Jennings

National University of Ireland, Galway, Gaillimh, Connaught, Ireland

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Publications (104)237.81 Total impact

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    ABSTRACT: Cluster analysis of particle number size distributions from background sites across Europe is presented. This generated a total of nine clusters of particle size distributions which could be further combined into two main groups, namely: a south-to-north category (four clusters) and a west-to-east category (five clusters). The first group was identified as most frequently being detected inside and around northern Germany and neighbouring countries, showing clear evidence of local afternoon nucleation and growth events that could be linked to movement of air masses from south to north arriving ultimately at the Arctic contributing to Arctic haze. The second group of particle size spectra proved to have narrower size distributions and collectively showed a dependence of modal diameter upon the longitude of the site (west to east) at which they were most frequently detected. These clusters indicated regional nucleation (at the coastal sites) growing to larger modes further inland. The apparent growth rate of the modal diameter was around 0.6–0.9 nm* h^(−1) . Four specific air mass back-trajectories were successively taken as case studies to examine in real time the evolution of aerosol size distributions across Europe. While aerosol growth processes can be observed as aerosol traverses Europe, the processes are often obscured by the addition of aerosol by emissions en route. This study revealed that some of the 24 stations exhibit more complex behaviour than others, especially when impacted by local sources or a variety of different air masses. Overall, the aerosol size distribution clustering analysis greatly simplifies the complex data set and allows a description of aerosol aging processes, which reflects the longer-term average development of particle number size distributions as air masses advect across Europe.
    ATMOSPHERIC CHEMISTRY AND PHYSICS 04/2014; Atmos. Chem. Phys., 14, 4327-4348, 2014(14):4327-4348. · 5.51 Impact Factor
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    Atmospheric Chemistry and Physics 01/2014; 14:4679-4713. · 4.88 Impact Factor
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    ABSTRACT: The atmospheric concentration of elemental carbon (EC) in Europe during the six-year period 2005–2010 has been simulated with the EMEP MSC-W model. The model bias compared to EC measurements was less than 20 % for most of the examined sites. The model results suggest that fossil fuel combustion is the dominant source of EC in most of Europe but that there are important contributions also from residential wood burning during the cold seasons and, during certain episodes, also from open biomass burning (wildfires and agricultural fires). The modelled contributions from open biomass fires to ground level concentrations of EC were small at the sites included in the present study, < 3 % of the long-term average of EC in PM 10 . The modelling of this EC source is subject to many uncertainties, and it was likely underestimated for some episodes. EC measurements and modelled EC were also compared to optical measurements of black carbon (BC). The relationships between EC and BC (as given by mass absorption cross section, MAC, values) differed widely between the sites, and the correlation between observed EC and BC is sometimes poor, making it difficult to compare results using the two techniques and limiting the comparability of BC measurements to model EC results. A new bottom-up emission inventory for carbonaceous aerosol from residential wood combustion has been applied. For some countries the new inventory has substantially different EC emissions compared to earlier estimates. For northern Europe the most significant changes are much lower emissions in Norway and higher emissions in neighbouring Sweden and Finland. For Norway and Sweden, comparisons to source-apportionment data from winter campaigns indicate that the new inventory may improve model-calculated EC from wood burning. Finally, three different model setups were tested with variable atmospheric lifetimes of EC in order to evaluate the model sensitivity to the assumptions regarding hygroscopicity and atmospheric ageing of EC. The standard ageing scheme leads to a rapid transformation of the emitted hydrophobic EC to hygroscopic particles, and generates similar results when assuming that all EC is aged at the point of emission. Assuming hydrophobic emissions and no ageing leads to higher EC concentrations. For the more remote sites, the observed EC concentration was in between the modelled EC using standard ageing and the scenario treating EC as hydrophobic. This could indicate too-rapid EC ageing in the model in relatively clean parts of the atmosphere.
    Atmospheric Chemistry and Physics 09/2013; 13(17):8719-8738. · 5.51 Impact Factor
  • Aditya Vaishya, S. G. Jennings, C. D. O'Dowd
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    ABSTRACT: Aerosol light scattering measurements were carried out at the Global Atmosphere Watch (GAW) research station, Mace Head, on the west coast of Ireland. Analysis of ten years (2001-2010) of the aerosol light scattering coefficient (σscat) at 550nm reveals a strong seasonal trend with σscat values during the winter season being approximately three times that of the summer season. The σscat and the aerosol light backscattering coefficient (σbscat) for the winter (Low Biological Activity - LBA) and the summer (High Biological Activity-HBA) are dependent on the square of wind speed (U). Scattering properties for the LBA period are approximately twice those of the HBA period. 70% of the observed LBA-HBA scattering difference can be attributed to differences in refractive index alone, resulting from organicmatter enrichment during the HBA period.
    05/2013;
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    ABSTRACT: Primary-produced sea-spray is typically composed of sea-salt, but in biologically-active regions, the spray can become enriched with organic matter which reduces hygroscopicity of sea-spray, thereby having a potential impact on aerosol scattering. This study shows that scattering enhancement of marine aerosol, as a function of increasing relative humidity, is reduced when enriched with organics whose results are used to develop a new hygroscopicity growth-factor parameterization for sea-spray enriched in organic matter. The parameterization reveals a dual state which flips from high-hygroscopicity and high-scattering enhancement to low-hygroscopicity and low-scattering enhancement as the organic volume fraction increases from below ~ 0.55 to above ~ 0.55. In terms of organic enrichment, the effect on Top of Atmosphere (TOA) direct radiative forcing (ΔF) is to reduce the cooling contribution of sea-spray by ~ 5.5 times compared to pure sea-salt spray. The results presented here highlight a significant coupling between the marine biosphere and the direct radiative budget through alteration of sea-spray chemical composition, potentially leading to accelerated global warming should biological activity increase with future projected temperature increases.
    05/2013;
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    ABSTRACT: A regional climate model is used to assess changes in atmospheric ozone for the years 2030, 2050 and 2100 relative to 2006 brought about by changes in meteorology and emissions. The simulations are evaluated against ozone measurements for 2006, exhibiting good agreement between the model-predicted measurements and the measured annual cycles. Under the RCP6 emission scenario used in these simulations, average ozone mixing ratios are set to reduce by 2.0 ppb over domains encompassing Europe and the North East Atlantic between 2006 and 2100 with the most significant decrease occurring after 2050 due to the pattern in changing emissions. Peak reductions of more than 8 ppb are observed during summer time over mainland Europe by 2100. Model output was studied for three relevant sub-domains, namely the North East Atlantic, Ireland and Europe. The relative contribution of changes in both emissions and meteorology is assessed. Over the whole domain, changing emissions are predominantly responsible for changes in surface ozone; although over the North East Atlantic domain, the changing emissions do not perturb surface ozone trends and the decrease in 2100 levels is entirely attributable to changing meteorology.
    Atmospheric Environment 04/2013; 69:198–210. · 3.11 Impact Factor
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    ABSTRACT: We have analysed the trends of total aerosol parti-cle number concentrations (N) measured at long-term mea-surement stations involved either in the Global Atmosphere Watch (GAW) and/or EU infrastructure project ACTRIS. The sites are located in Europe, North America, Antarc-tica, and on Pacific Ocean islands. The majority of the sites showed clear decreasing trends both in the full-length time-series, and in the intra-site comparison period of 2001–2010, especially during the winter months. Several potential driv-ing processes for the observed trends were studied, and even though there are some similarities between N trends and air temperature changes, the most likely cause of many north-ern hemisphere trends was found to be decreases in the an-thropogenic emissions of primary particles, SO 2 or some co-emitted species. We could not find a consistent agreement between the trends of N and particle optical properties in the few stations with long timeseries of all of these properties. The trends of N and the proxies for cloud condensation nu-clei (CCN) were generally consistent in the few European stations where the measurements were available. This work provides a useful comparison analysis for modelling studies of trends in aerosol number concentrations.
    Atmospheric Chemistry and Physics 02/2013; 13:1-22. · 5.51 Impact Factor
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    ABSTRACT: Currently many ground-based atmospheric stations include in-situ measurements of aerosol physical and optical properties, resulting in more than 20 long-term (>10 yr) aerosol measurement sites in the Northern Hemisphere and Antarctica. Most of these sites are located at remote locations and monitor the aerosol particle number concentration, wavelength-dependent light scattering, backscattering, and absorption coefficients. The existence of these multi-year datasets enables the analysis of long-term trends of these aerosol parameters of the derived light scattering Ångström exponent and backscatter fraction. Since the aerosol variables are not normally distributed, three different methods (the seasonal Mann-Kendall test associated with the Sen's slope, the generalized least squares fit associated with an autoregressive bootstrap algorithm for confidence intervals, and the least-mean square fit applied to logarithms of the data) were applied to detect the long-term trends and their magnitudes for each month. To allow a comparison among measurement sites with varying length of data records, trends on the most recent 10 and 15 yr periods were calculated. No significant trends were found for the three continental European sites. Statistically significant trends were found for the two European marine sites but the signs of the trends varied with aerosol property and location. Statistically significant decreasing trends for both scattering and absorption coefficient were found for most North American stations, although positive trends were found for a few desert and high-altitude sites. No significant trends in scattering coefficient were found for the Arctic or Antarctic stations, whereas the Arctic station had a negative trend in absorption coefficient.
    Atmospheric Chemistry and Physics 01/2013; 13(2):869-894. · 4.88 Impact Factor
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    ABSTRACT: Sixteen years (1994 – 2009) of ozone profiling by ozonesondes at Valentia Meteorological and Geophysical Observatory, Ireland (51.94° N, 10.23° W) along with a co-located MkIV Brewer spectrophotometer for the period 1993–2009 are analyzed. Simple and multiple linear regression methods are used to infer the recent trend, if any, in stratospheric column ozone over the station. The decadal trend from 1994 to 2010 is also calculated from the monthly mean data of Brewer and column ozone data derived from satellite observations. Both of these show a 1.5 % increase per decade during this period with an uncertainty of about ±0.25 %. Monthly mean data for March show a much stronger trend of ~ 4.8 % increase per decade for both ozonesonde and Brewer data. The ozone profile is divided between three vertical slots of 0–15 km, 15–26 km, and 26 km to the top of the atmosphere and a 11-year running average is calculated. Ozone values for the month of March only are observed to increase at each level with a maximum change of +9.2 ± 3.2 % per decade (between years 1994 and 2009) being observed in the vertical region from 15 to 26 km. In the tropospheric region from 0 to 15 km, the trend is positive but with a poor statistical significance. However, for the top level of above 26 km the trend is significantly positive at about 4 % per decade. The March integrated ozonesonde column ozone during this period is found to increase at a rate of ~6.6 % per decade compared with the Brewer and satellite positive trends of ~5 % per decade.
    Journal of Atmospheric Chemistry 01/2013; · 1.33 Impact Factor
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    ABSTRACT: We have analysed the trends of total aerosol particle number concentrations (N) measured at long-term measurement stations involved either in the Global Atmosphere Watch (GAW) and/or EU infrastructure project ACTRIS. The sites are located in Europe, North America, Antarctica, and on Pacific Ocean islands. The majority of the sites showed clear decreasing trends both in the full-length time-series, and in the intra-site comparison period of 2001-2010, especially during the winter months. Several potential driving processes for the observed trends were studied, and even though there are some similarities between N trends and air temperature changes, the most likely cause of many Northern Hemisphere trends was found to be decreases in the anthropogenic emissions of primary particles, SO2 or some co-emitted species. We could not find a consistent agreement between the trends of N and particle optical properties in the few stations with long timeseries of all of these properties. The trends of N and the proxies for cloud condensation nuclei (CCN) were generally consistent in the few European stations where the measurements were available. This work provides a useful comparison analysis for modelling studies of trends in aerosol number concentrations.
    Atmospheric Chemistry and Physics 08/2012; 12(8):20849-20899. · 4.88 Impact Factor
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    ABSTRACT: Mobility particle size spectrometers often referred to as DMPS (Differential Mobility Particle Sizers) or SMPS (Scanning Mobility Particle Sizers) have found a wide range of applications in atmospheric aerosol research. However, comparability of measurements conducted world-wide is hampered by lack of generally accepted technical standards and guidelines with respect to the instrumental set-up, measurement mode, data evaluation as well as quality control. Technical standards were developed for a minimum requirement of mobility size spectrometry to perform long-term atmospheric aerosol measurements. Technical recommendations include continuous monitoring of flow rates, temperature, pressure, and relative humidity for the sheath and sample air in the differential mobility analyzer. We compared commercial and custom-made inversion routines to calculate the particle number size distributions from the measured electrical mobility distribution. All inversion routines are comparable within few per cent uncertainty for a given set of raw data. Furthermore, this work summarizes the results from several instrument intercomparison workshops conducted within the European infrastructure project EUSAAR (European Supersites for Atmospheric Aerosol Research) and ACTRIS (Aerosols, Clouds, and Trace gases Research InfraStructure Network) to determine present uncertainties especially of custom-built mobility particle size spectrometers. Under controlled laboratory conditions, the particle number size distributions from 20 to 200 nm determined by mobility particle size spectrometers of different design are within an uncertainty range of around ±10% after correcting internal particle losses, while below and above this size range the discrepancies increased. For particles larger than 200 nm, the uncertainty range increased to 30%, which could not be explained. The network reference mobility spectrometers with identical design agreed within ±4% in the peak particle number concentration when all settings were done carefully. The consistency of these reference instruments to the total particle number concentration was demonstrated to be less than 5%. Additionally, a new data structure for particle number size distributions was introduced to store and disseminate the data at EMEP (European Monitoring and Evaluation Program). This structure contains three levels: raw data, processed data, and final particle size distributions. Importantly, we recommend reporting raw measurements including all relevant instrument parameters as well as a complete documentation on all data transformation and correction steps. These technical and data structure standards aim to enhance the quality of long-term size distribution measurements, their comparability between different networks and sites, and their transparency and traceability back to raw data.
    Atmospheric Measurement Techniques 01/2012; 5(3):657-685. · 3.21 Impact Factor
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    ABSTRACT: a b s t r a c t The recent eruption of Iceland's Eyjafjallajökull volcano caused extensive disruption across Europe. In this paper, we describe the volcanic ash parameterisation incorporated in the regional climate model (REMOTE) for forecasting volcanic ash dispersion. We investigate model sensitivity to emission param-eters including eruption column height and vertical release distribution. Model results over a number of key ash incursion events are assessed in terms of agreement with both ground based measurements and retrieved LIDAR data at a number of European sites.
    Atmospheric Environment 10/2011; 48:143-151. · 3.11 Impact Factor
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    ABSTRACT: Dual carbon isotope analysis of marine aerosol samples has been performed for the first time demonstrating a potential in organic matter apportionment between three principal sources: marine, terrestrial (non-fossil) and fossil fuel due to unique isotopic signatures. The results presented here, utilising combinations of dual carbon isotope analysis, provides conclusive evidence of a dominant biogenic organic fraction to organic aerosol over biologically active oceans. In particular, the NE Atlantic, which is also subjected to notable anthropogenic influences via pollution transport processes, was found to contain 80 % organic aerosol matter of biogenic origin directly linked to plankton emissions. The remaining carbonaceous aerosol was of terrestrial origin. By contrast, for polluted air advected out from Europe into the NE At-lantic, the source apportionment is 30 % marine biogenic, 40 % fossil fuel, and 30 % continental non-fossil fuel. The dominant marine organic aerosol source in the atmosphere has significant implications for climate change feedback pro-cesses.
    ATMOSPHERIC CHEMISTRY AND PHYSICS 09/2011; 11:8593-8606. · 5.51 Impact Factor
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    ABSTRACT: Dual carbon isotope analysis has been performed for the first time demonstrating a potential in organic matter apportionment between three principal sources: marine, terrestrial (non-fossil) and fossil fuel due to unique isotopic signatures. The results presented here, utilising combinations of dual carbon isotope analysis, provides a conclusive evidence of a dominant biogenic organic fraction to organic aerosol over biologically active oceans. In particular, the NE Atlantic, which is also subjected to notable anthropogenic influences via pollution transport processes, was found to contain 80% organic aerosol matter of biogenic origin directly linked to plankton emissions. The remaining carbonaceous aerosol was of fossil-fuel origin. By contrast, for polluted air advecting out from Europe into the NE Atlantic, the source apportionment is 30% marine biogenic, 40% fossil fuel, and 30% continental non-fossil fuel. The dominant marine organic aerosol source in the atmosphere has significant implications for climate change feedback processes.
    Atmospheric Chemistry and Physics 01/2011; · 4.88 Impact Factor
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    ABSTRACT: In this study, the concentrations of total gaseous mercury in baseline air masses arriving at Mace Head, Ireland after having traversed the thousands of kilometres uninterrupted fetch of the North Atlantic Ocean, have been used for the assessment of possible trends in the atmospheric mercury background concentration over a 14-year period (i.e., 1996–2009), a statistically significant negative (downwards) trend of −0.028 ± 0.01 ng m−3 yr−1, representing a trend of 1.6–2.0% per year, has been detected in the total gaseous mercury levels in these baseline air masses. These findings are set in the context of the available literature studies of atmospheric Hg trends.Highlights► Our data set is the longest existing time series for Hg in temperate background air. ► More than 40 000 concentration measurements could be attributed to NH background air. ► We find a downward trend of 1.6–2.0%/yr over the 14 years measurement period. ► This decline is large in comparison to that seen in other trace gases. ► This decline contradicts current global emission inventories for mercury.
    Atmospheric Environment 01/2011; 45(20):3475-3480. · 3.11 Impact Factor
  • Aditya Vaishya, S. G. Jennings, Colin O'Dowd
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    ABSTRACT: Aerosol light scattering measurements were carried out using a TSI 3563 Nephelometer at the Mace Head Atmospheric Research Station, on the west coast of Ireland from year 2001–2010. A strong seasonal trend in the aerosol light scattering coefficient at 550 nm ( σ scat ), for clean marine air masses, is observed with a high σ scat value, [average (geometric mean)] of 35.3 Mm−1 (29.5 Mm−1), in January and a low σ scat value of 13.7 Mm−1 (10.2 Mm−1), in July. This near threefold increase in the σ scat value during the winter season is because of the large contribution of wind-speed generated sea-salt particles in the marine boundary layer. A high positive correlation coefficient of 0.82 was found between the percentage occurrence of relatively large Ångström exponent (Å) values (>1.2) and the percentage occurrence of lower σ scat values (5–15 Mm−1) in the summer season. σ scat and wind-speed have a high positive correlation coefficient of 0.88 whereas Å and wind-speed have a negative correlation coefficient of −0.89. Å values during the summer months indicate the dominance of sub- μ m particles thus indicating the contribution of non-sea-salt sulphate and organics towards the σ scat as these species show an enhanced concentration during the summer months.
    Advances in Meteorology 01/2011; 2011. · 1.24 Impact Factor
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    ABSTRACT: As part of the EUCAARI Intensive Observing Period, a 4-week campaign to measure aerosol physical, chemical and optical properties, atmospheric structure, and cloud microphysics was conducted from mid-May to mid-June, 2008 at the Mace Head Atmospheric Research Station, located at the interface of Western Europe and the N. E. Atlantic and centered on the west Irish coastline. During the campaign, continental air masses comprising both young and aged continental plumes were encountered, along with polar, Arctic and tropical air masses. Polluted-continental aerosol concentrations were of the order of 3000 cm−3, while background marine air aerosol concentrations were between 400–600 cm−3. The highest marine air concentrations occurred in polar air masses in which a 15 nm nucleation mode, with concentration of 1100 cm−3, was observed and attributed to open ocean particle formation. Continental air submicron chemical composition (excluding refractory sea salt) was dominated by organic matter, closely followed by sulphate mass. Although the concentrations and size distribution spectral shape were almost identical for the young and aged continental cases, hygroscopic growth factors (GF) and cloud condensation nuclei (CCN) to total condensation nuclei (CN) concentration ratios were significantly less in the younger pollution plume, indicating a more oxidized organic component to the aged continental plume. The difference in chemical composition and hygroscopic growth factor appear to result in a 40–50% impact on aerosol scattering coefficients and Aerosol Optical Depth, despite almost identical aerosol microphysical properties in both cases, with the higher values been recorded for the more aged case. For the CCN/CN ratio, the highest ratios were seen in the more age plume. In marine air, sulphate mass dominated the sub-micron component, followed by water soluble organic carbon, which, in turn, was dominated by methanesulphonic acid (MSA). Sulphate concentrations were highest in marine tropical air – even higher than in continental air. MSA was present at twice the concentrations of previously-reported concentrations at the same location and the same season. Both continental and marine air exhibited aerosol GFs significantly less than ammonium sulphate aerosol pointing to a significant organic contribution to all air mass aerosol properties.
    ATMOSPHERIC CHEMISTRY AND PHYSICS 09/2010; 10(10):8413-35. · 5.51 Impact Factor
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    ABSTRACT: No abstract available.
    ATMOSPHERIC CHEMISTRY AND PHYSICS 09/2010; 10(17):8549-8549. · 5.51 Impact Factor

Publication Stats

2k Citations
237.81 Total Impact Points

Institutions

  • 1993–2013
    • National University of Ireland, Galway
      • School of Physics
      Gaillimh, Connaught, Ireland
  • 2008
    • University College Cork
      • Department of Physics
      Cork, M, Ireland
  • 2002
    • University of Bristol
      • School of Chemistry
      Bristol, ENG, United Kingdom
    • Hungarian Academy of Sciences
      • Section of Environmental and Earth Sciences
      Budapeŝto, Budapest, Hungary
  • 2001
    • Paul Scherrer Institut
      • Laboratory of Atmospheric Chemistry (LAC)
      Aargau, Switzerland