Abstract
Abstract. Chemical composition and hygroscopicity closure of marine aerosol in high time resolution has not been achieved yet due to the difficulty involved in measuring the refractory sea-salt concentration in near-real time. In this study, attempts were made to achieve closure for marine aerosol based on a humidified tandem differential mobility analyser (HTDMA) and a high-resolution time-of-flight aerosol mass spectrometer (AMS) for wintertime aerosol at Mace Head, Ireland. The aerosol hygroscopicity was examined as a growth factor (GF) at 90 % relative humidity (RH). The corresponding GFs of 35, 50, 75, 110 and 165 nm particles were 1.54±0.26, 1.60±0.29, 1.66±0.31, 1.72±0.29 and 1.78±0.30 (mean ± standard deviation), respectively. Two contrasting air masses (continental and marine) were selected to study the temporal variation in hygroscopicity; the results demonstrated a clear diurnal pattern in continental air masses, whereas no diurnal pattern was found in marine air masses. In addition, wintertime aerosol was observed to be largely externally mixed in both of the contrasting air masses. Concurrent high time resolution PM1 (particulate matter <1 µm) chemical composition data from combined AMS and MAAP measurements, comprising organic matter, non-sea-salt sulfate, nitrate, ammonium, sea salt and black carbon (BC), were used to predict aerosol hygroscopicity with the Zdanovskii–Stokes–Robinson (ZSR) mixing rule. Overall, good agreement (an R2 value of 0.824 and a slope of 1.02) was found between the growth factor of 165 nm particles measured by the HTDMA (GF_HTDMA) and the growth factor derived from the AMS + MAAP bulk chemical composition (GF_AMS). Over 95 % of the estimated GF values exhibited less than a 10 % deviation for the whole dataset, and this deviation was mostly attributed to the neglected mixing state as a result of the bulk PM1 composition.
Highlights
Marine aerosol is probably the most important component of natural aerosol in terms of climate effect (O’Dowd and de Leeuw, 2007), because over 70 % of the Earth’s surface is covered by global ocean
Data from a humidified tandem differential mobility analyser (HTDMA) and an aerosol mass spectrometer (AMS) instrument deployed at Mace Head Atmospheric Research Station were used to characterise aerosol hygroscopicity and to elucidate the link with aerosol chemical composition by taking the advantage of the high temporal resolution of the two instruments
In winter, which is a period of low biological activity at Mace Head, the sampled aerosols were mostly externally mixed, as revealed by the growth factor (GF)-PDFs
Summary
Marine aerosol is probably the most important component of natural aerosol in terms of climate effect (O’Dowd and de Leeuw, 2007), because over 70 % of the Earth’s surface is covered by global ocean. There are two ways that marine aerosol can exert its impact on global climate: (1) by scattering the incoming solar radiation and (2) by acting as cloud condensation nuclei (CCN). Hygroscopicity – the ability of aerosol to take up water vapour – plays a significant role in both. Hygroscopicity affects the mass of aerosols by increasing the aerosol liquid water content and enhancing particle light scattering, thereby cooling the atmosphere directly. Hygroscopicity has a large impact on CCN activa-. W. Xu et al.: Aerosol hygroscopicity and its link to chemical composition tion and cloud droplet formation, modifying cloud radiative forcing and the hydrological cycle (Twomey, 1974, 1977)
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