Abstract
Abstract. A wideband integrated bioaerosol sensor (WIBS-4) was deployed in Haulbowline Island, Cork Harbour, to detect fluorescence particles in real time during July and September 2011. A scanning mobility particle sizer (SMPS) was also installed providing sizing analysis of the particles over the 10–450 nm range. During the campaign, multiple fog formation events occurred; they coincided with dramatic increases in the recorded fluorescent particle counts. The WIBS sizing and fluorescence intensity profiles indicated that the origin of the signals was potentially non-biological in nature (i.e. PBAPs, primary biological aerosol particles). Furthermore, the data did not support the presence of known fluorescing chemical particles like SOA (secondary organic aerosol). Complementary laboratory studies showed that the field results could potentially be explained by the adsorption of molecular iodine onto water droplets to form I2 ⋅ (H2O)x complexes. The release of iodine into the coastal atmosphere from exposed kelp at low tides has been known for many years. This process leads to the production of small IxOy particles, which can act as cloud condensation nuclei (CCN). While the process of molecular iodine release from coastal kelp sources, subsequent particle formation, and the observations of sea mists and fogs have been studied in detail, this study provides a potential link between the three phenomena. Of mechanistic interest is the fact that molecular iodine included into (rather than on) water droplets does not appear to fluoresce as measured using WIBS instrumentation. The study indicates a previously unsuspected stabilizing transport mechanism for iodine in the marine environment. Hence the stabilization of the molecular form would allow its more extensive distribution throughout the troposphere before eventual photolysis.
Highlights
Atmospheric aerosols comprise a variety of chemical and biological components released from natural and anthropogenic sources
The results of the campaign reported here are related to a study mounted to obtain real-time number concentrations of primary biological aerosol particles (PBAPs) released at a coastal site, i.e. a location never investigated before in this context
The wideband integrated bioaerosol sensor model 4 (WIBS4) is a prototype real-time biological particle sensor developed by the University of Hertfordshire in the UK and used in many field and laboratory campaigns directed toward the detection of bioaerosols over the last 10 years (Kaye et al, 2005; Gabey et al, 2010; Stanley et al, 2011; Healy et al, 2012a, b)
Summary
Atmospheric aerosols comprise a variety of chemical and biological components released from natural and anthropogenic sources. They are released into the air by bubble-bursting processes which produce seaspray droplets that evaporate, leading to a wide distribution of particle sizes ranging from ∼ 10 nm to many microns These dispersions represent some of the first aerosol types to be systematically investigated because of the historical observations of sea fogs. Transparent coastal mists have long been noted and observed to act as precursors to the development of fogs that form at a humidity as low as 70 % (Twomey et al, 1955) These coastal mists represent a situation when condensation and evaporation are competing in a region where breaking waves are dominant, thereby leading to the release of large densities of sea-salt particles. The results of the campaign reported here are related to a study mounted to obtain real-time number concentrations of PBAP released at a coastal site, i.e. a location never investigated before in this context
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