Aerosol hygroscopicity and its link to chemical composition in the coastal atmosphere of Mace Head: marine and continental air masses

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