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

Abstract

Abstract. Atmospheric aerosols have been sampled and characterised at the Mace Head north-east (NE) Atlantic atmospheric research station since 1958, with many interesting phenomena being discovered. However, with the range of new discoveries and scientific advances, there has been a range of concomitant criticisms challenging the representativeness of aerosol sampled at the station compared to that of aerosol over the pristine open-ocean. Two recurring criticisms relate to the lack of representativeness due to potentially enhanced coastal sources, possibly leading to artificially high values of aerosol concentrations, and to the influence of long-range transport of anthropogenic or continental aerosol and its potential dominance over, or perturbation of, a natural marine aerosol signal. Here, we review the results of previous experimental studies on marine aerosols over the NE Atlantic and at Mace Head with the aim of evaluating their representativeness relative to that of a pristine openocean aerosol, i.e. with negligible anthropogenic/continental influence. Particular focus is given to submicron organic matter (OM) aerosol. In summary, no correlation was found between OM and black carbon (BC) in marine air conforming to clean-air sampling criteria, either at BC levels of 0-15 or 15-50 ng m −3 , suggesting that OM concentrations, up to observed peak values of 3.8 µg m −3 , are predominantly natural in origin. Sophisticated carbon isotope analysis and aerosol mass spectral finger printing techniques corroborate the conclusion that there is a predominant natural source of OM, with 80 % biogenic source apportionment being observed for general clean-air conditions, rising to ∼ 98 % during specific primary marine organic plumes when peak OM mass concentrations > 3 µg m −3 are observed. Similarly, a maximum contribution of 20 % OM mass coming from non-marine sources was established by dual carbon isotope analysis. Further, analysis of a series of experiments conducted at Mace Head conclude that negligible coastal, surf zone, or tidal effects are discernible in the secondary or primary aerosol mass residing in the submicron size range for sampling heights of 7 m and above. The Mace Head marine-air criteria ensure anthropogenic and coastal effects are sufficiently minimised so as to guarantee a predominant, and sometimes overwhelming, natural marine aerosol contribution to the total aerosol population when the criteria are adhered to.

Shipborne observations reveal contrasting Arctic marine, Arctic terrestrial and Pacific marine aerosol properties

“…environments had a range of approximately three orders of magnitude (~10 1 − 10 cm -3 ). In most cases, the CN 2.5 and CN 10 concentrations were less than ~2000 cm -3 , with averages of 505 ± 280 and ± 264 cm -3 , respectively, which were in agreement with those reported in previous studies conducted at other Arctic stations (Asmi et al, 2016;Burkart et al, 2017;Freud et al, 2017) and remote marine regions (O'Dowd et al, 2014;Sellegri et al, 2006;Jang et al, 2019;Yum et al, 1998;Hudson and Yum, 2002). For example, four years of observational data from the Arctic Climate Observatory in Tiksi, Russia, showed that the monthly median CN concentration ranged from ~184 cm -3 in November to ~724 cm -3 in July (Asmi et al, 2016).…”

Effects of two different biogenic emission models on modelled ozone and aerosol concentrations in Europe

“…7) on the other hand, were lower than the measured equivalent black carbon (EBC) in general but followed the temporal variation very well. In a study about the aerosols at Mace Head, O'Dowd et al (2014) reported that EBC measurements can significantly overestimate black carbon concentration by up to 50% or more. Overestimation of SIA could result from either too high precursor emissions or too much particle formation in the aqueous phase.…”

Source apportionment of the organic aerosol over the Atlantic Ocean from 53° N to 53° S: significant contributions from marine emissions and long-range transport

“…On the other hand, sea surface water is also a reservoir of organic matter that can be injected into the air and enriched in the particles (Aller et al, 2005;Kuznetsova et al, 2005;Schmitt-Kopplin et al, 2012;. Organic matter has been observed to dominate the particle mass (up to 77 %) during phytoplankton bloom periods at a coastal station in Ireland (O'Dowd et al, 2004;Ovadnevaite et al, 2011). However, many marine aerosol studies were based on observations of islands or in coastal areas, where biological activities are much higher than the remote ocean (as illustrated by global maps of chlorophyll a -Chl a: https://earthobservatory.nasa.gov/GlobalMaps/view.…”

“…Significant impacts from ship and continental emissions were observed over the Pacific and Atlantic (63 % of the sampling time; Frossard et al, 2014), the Arctic (Chang et al, 2011), and the North Pa-cific between southern Asia and northern Japan (Choi et al, 2017). Nevertheless, there are still some regions with little anthropogenic impact on marine aerosols, such as the station on the coast of Ireland in the northeastern Atlantic (Ceburnis et al, 2011;O'Dowd et al, 2014). Due to the paucity of ship-based measurements, the non-marine influence on MBL aerosol particles is still unknown, especially for a large area of the oceans.…”