T.G. Spain

Long-term measurements of atmospheric mercury at Mace Head, Irish west coast, between 1995 and 2001

Abstract Monitoring of atmospheric mercury concentrations has been carried out at the Mace Head atmospheric research station on the west coast of Ireland between September 1995 and December 2001. Measurements were carried out with a time resolution of 15 min . No trend in the concentration levels has been detected during the measurement period, with the annual average concentrations remaining constant at 1.75 ng m −3 . A slight increase in the concentration levels is derived, if only clean sector filtered air masses clearly of marine origin are used. The Mace Head data set shows a seasonal pattern with higher monthly mean concentrations in the winter months. Comparison with two continental sites in Sweden shows, that atmospheric mercury concentrations at the western inflow boundary are on an average higher than those at the two continental sites, expressing a west to east decreasing concentration gradient. At Mace Head, no indications for so-called Mercury Depletion Events (MDEs), recently reported for a number of sites in the Arctic and in the Antarctic, have been found between 1995 and 2001.

Black carbon measurements at Mace Head, 1989–1996

Black carbon mass concentrations have been measured using an aethalometer at Mace Head on the west coast of Ireland on an almost continuous basis from February 1989 to June 1996. The purpose of this paper is to report on the monthly averaged black carbon concentration at this site over the 7 year period and to examine the influence of air mass on the black carbon mass concentration. The seasonal variation of black carbon mass concentration for clean marine and continental air masses is also investigated.

Microphysical and physico-chemical characterization of atmospheric marine and continental aerosol at Mace Head

Abstract Measurements of the aerosol particle size, aerosol volume distribution and aerosol volatility (diameter range 0.1–3.0 μm), aerosol mass (diameter range 0.06–16.0 μm), condensation nuclei (CN) and cloud condensation nuclei (CCN), and black carbon (BC) mass concentration at Mace Head during the EU project “Background Maritime Contribution to Atmospheric Pollution in Europe” (BMCAPE), obtained over four intensive campaigns during the period between November 1993 and August 1994, are presented. Marine air was found to possess mean accumulation mode (ACM) aerosol particle number concentration., N , of between 100 and 160 cm −3 for the winter and summer seasons. Marine ACM mass ranged in value from about 0.8 to 6 μg m −3 . Marine air was found to contain black carbon with episodic mean mass concentrations generally in the range 5–40 ng m −3 a. The impact of black carbon on the marine environment is also reflected by the moderately positive correlation ( r 2 in the range 0.23–0.44) found between marine ACM number concentration and BC mass loading, with a higher correlation ( r 2 = 0.55) found for winter continental air. Black carbon accounted for between 0.6% and 1.2% of the ACM mass loading for marine aerosol at Mace Head, increasing to between 4% and 6% for continental air. Arithmetic mean values of ACM number concentration N and BC mass concentration agree quite well with results from a few other investigators of marine atmospheric aerosol in the North Atlantic.

Mass measurements of aerosol at mace head, on the west coast of Ireland

Abstract Aerosol mass/size measurements have been carried out at the Mace Head research station, on the west coast of Ireland, for a period of over two years. Mass/size distributions were obtained in the size range 0.06–10 μm using Berner low-pressure cascade impactor systems. The distributions obtained reflect the different types of air mass which are encountered at Mace Head. Westerly winds are dominant at the site with the associated air masses being typically maritime. Unimodal mass/size distributions with the peak mass concentration occurring principally in the 2–4 μm size range were characteristic of these conditions. Continental air masses from Europe are typified by mass/size distributions which have peak values in the submicron size range. Distinct bimodal distributions were obtained when aerosols were collected from a mixture of air mass types. Overall, the mass concentration was found to vary between approximately 2 and 45 μg m−3 A wide variation in mass concentration values were measured at similar wind speeds. However, a trend towards higher mass concentrations at higher wind speeds was observed in the coarse mass fraction contribution (> 1 μm) from westerly maritime air masses at higher wind speeds. A drop-off in mass concentration was observed at wind speeds greater than approximately 11 m s−1 This is attributed to the cut-off characteristic of the PM10 inlet used with the impactor system. High mass concentrations during long term pollution events at Mace Head were also observed with the collected aerosol resident principally in the submicron size range during these conditions.

Estimation of hydrogen deposition velocities from 1995–2008 at Mace Head, Ireland using a simple box model and concurrent ozone depositions

During stable nocturnal inversions with low wind speeds, we observed strong depletions of both hydrogen and ozone caused by deposition to the peat bogs in the vicinity of the Mace Head Atmospheric Research Station, Connemara, County Galway, Ireland. From these temporally correlated fluxes and using a simple box model, we have estimated the strength of the molecular hydrogen soil sink over a 14-yr period (1995-2008). Over this entire period 269 nocturnal deposition events were identified that satisfied the strict selection criteria. The average hydrogen deposition velocity determined from these events was 0.53 mm s-1, covering a range of 0.18-1.29 mm s-1, which is in agreement with the range of deposition velocities reported in the literature for similar peaty biomes. By annually averaging all of the nocturnal inversion events over the most seasonally active period from April-September we reveal a positive correlation with ambient temperature in the relative deposition velocities of hydrogen and ozone, which is not readily apparent in all of the individual events. Furthermore, average hydrogen deposition velocities and accumulated rainfall from 48 h before and during each event were to a reasonable extent anti-correlated. However, due to the large uncertainties in determining monthly mean H2 deposition velocities there is no statistically significant trend in the hydrogen deposition velocities over time.