Chemical and physical characteristics of aerosol particles at a remote coastal location, Mace Head, Ireland, during NAMBLEX

[摘要] A suite of aerosol physical and chemical measurements were made atthe Mace Head Atmospheric Research Station, Co. Galway, Ireland, acoastal site on the eastern seaboard of the north Atlantic Oceanduring NAMBLEX. The data have been used in this paper to show thatover a wide range of aerosol sizes there is no impact of theinter-tidal zone or the surf zone on measurements made at 7 m aboveground level or higher. During the measurement period a range of airmass types were observed. During anticyclonic periods and conditionsof continental outflow Aitken and accumulation mode were enhanced bya factor of 5 compared to the marine sector, whilst coarse modeparticles were enhanced during westerly conditions. Baseline marineconditions were rarely met at Mace Head during NAMBLEX and high windspeeds were observed for brief periods only.The NAMBLEX experiment focussed on a detailed assessment ofphotochemistry in the marine environment, investigating the linkagebetween the HO_x and the halogen radical cycles.Heterogeneous losses are important in both these cycles.In thispaper loss rates of gaseous species to aerosol surfaces werecalculated for a range of uptake coefficients. Even when theaccommodation coefficient is unity, lifetimes due to heterogeneousloss of less than 10 s were never observed and rarely were theyless than 500 s. Diffusional limitation to mass transfer isimportant in most conditions as the coarse mode is alwayssignificant. We calculate a minimum overestimate of 50% in the lossrate if this is neglected and so it should always be considered whencalculating loss rates of gaseous species to particle surfaces.HO₂ and HOI have accommodation coefficients of around0.03 and hence we calculate lifetimes due to loss to particlesurfaces of 2000 s or greater under the conditions experiencedduring NAMBLEX.Aerosol composition data collected during this experiment providerepresentative information on the input aerosol characteristics towestern Europe. During NAMBLEX the submicron aerosol waspredominately acidified sulphate and organic material, which wasmost likely internally mixed. The remaining accumulation modeaerosol was sea salt.The organic and sulphate fractions wereapproximately equally important, though the mass ratio variesconsiderably between air masses. Mass spectral fingerprints of theorganic fraction in polluted conditions are similar to thoseobserved at other locations that are characterised by agedcontinental aerosol. In marine conditions, the background input ofbothsulphate and organic aerosol into Europe was observed to bebetween 0.5 and 1 µg m⁻³. Key differences in the massspectra were observed during the few clean periods but wereinsufficient to ascertain whether these changes reflect differencesin the source fingerprint of the organic aerosol.The coarse modewas composed of sea salt and showed significant displacement ofchloride by nitrate and to a lesser extent sulphate in pollutedconditions.

[学科分类] 大气科学