Aerosol properties associated with air masses arriving into the North East Atlantic during the 2008 Mace Head EUCAARI intensive observing period: an overview

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

Do anthropogenic, continental or coastal aerosol sources impact on a marine aerosol signature at Mace Head?

“…Organo-nitrogen, in the form of dimethyl amine (DMA) is also present to a lesser degree (Facchini et al, 2008a). More often than not, secondary inorganic aerosol such as nss sulfate dominates over secondary organic aerosol (SOA) as reported in Dall'Osto et al (2010); however, this study related to a brief snapshot relatively early in the season (late May-early June) when considering that peak productivity and peak OM enrichment occurs in August (noting that in Dall'Osto et al, only concentration and not enrichment was reported).…”

“…The choice of CN or particle number concentration and BC mass concentration thresholds is somewhat arbitrary; however, the choice of 700 CN m −3 is consistent with studies in the remote Southern Hemisphere; for example, O'Dowd et al (1997) found that total CN in pristine air below 53 • S over the South Atlantic and Weddell Sea, Antarctica, while generally less than 500 cm −3 , often reached 700 cm −3 in clean air outside new particle production events. Further, Dall'Osto et al (2010) found that the marine sector CN frequency distribution was bimodal, with a background mode concentration of 400-600 cm −3 . For EBC, O'Dowd et al (1993) found that NE Atlantic background marine air masses comprised EBC mass concentrations between 10 and 35 ng m −3 while the lowest EBC mass concentration in modified marine air was observed to be 220 ng m −3 .…”

Sources and mixing state of summertime background aerosol in the north-western Mediterranean basin

“…The authors expected this since the dust they observed was locally produced, unlike MSA. In contrast, internally mixed OC, sea salt, sulfate, titanium (dust) and MSA formed particles 1-2 µm in size at Mace Head during the EUCAARI project (Dall'Osto et al, 2010) and were associated with a period of subtropical maritime air originating from the Azores high-pressure region. The number of dust particles identified with the MSA query in this work were statistically too few to consider submicron/supermicron ratios.…”

Functionalization and fragmentation during ambient organic aerosol aging: application of the 2-D volatility basis set to field studies

“…The Mace Head Atmospheric Research Station is influenced by air masses that range from exceedingly clean (those that arrive directly from the west) to polluted continental outflow (Dall'Osto et al, 2010 (Morgan et al, 2010a), whereas in winter nitrate was the dominant component (Mensah et al, 2012). Dates from these sets were selected for model comparison in order to avoid regional stagnation events that would make simulation with a one-dimensional Lagrangian transport model exceedingly difficult.…”