Sources, Occurrence and Characteristics of Fluorescent Biological Aerosol Particles Measured Over the Pristine Southern Ocean

Abstract

In this study, we investigate the occurrence of primary biological aerosol particles (PBAP) over all sectors of the Southern Ocean (SO) based on a 90‐day data set collected during the Antarctic Circumnavigation Expedition (ACE) in austral summer 2016–2017. Super‐micrometer PBAP (1–16 µm diameter) were measured by a wide band integrated bioaerosol sensor (WIBS‐4). Low (3σ) and high (9σ) fluorescence thresholds are used to obtain statistics on fluorescent and hyper‐fluorescent PBAP, respectively. Our focus is on data obtained over the pristine ocean, that is, more than 200 km away from land. The results indicate that (hyper‐)fluorescent PBAP are correlated to atmospheric variables associated with sea spray aerosol (SSA) particles (wind speed, total super‐micrometer aerosol number concentration, chloride and sodium concentrations). This suggests that a main source of PBAP over the SO is SSA. The median percentage contribution of fluorescent and hyper‐fluorescent PBAP to super‐micrometer SSA was 1.6% and 0.13%, respectively. We demonstrate that the fraction of (hyper‐)fluorescent PBAP to total super‐micrometer particles positively correlates with concentrations of bacteria and several taxa of pythoplankton measured in seawater, indicating that marine biota concentrations modulate the PBAP source flux. We investigate the fluorescent properties of (hyper‐)fluorescent PBAP for several events that occurred near land masses. We find that the fluorescence signal characteristics of particles near land is much more variable than over the pristine ocean. We conclude that the source and concentration of fluorescent PBAP over the open ocean is similar across all sampled sectors of the SO.

Emission of primary bioaerosol particles from Baltic seawater

“…Furthermore, the corresponding size distribution is centered at 5 ± 2 μm which is similar to the size of bacteria agglomerates previously identified in both ambient coastal aerosol 51 and nascent SSA generated in laboratory experiments. 18,30 Interestingly, a number of recent studies suggest that PBAP constitutes only a small portion of the FP over or close to marine environments 27,49 and our data would appear to corroborate this: the PBAP contribution to the total FP was only 0.46% (0.04% of all CP).…”

“…Recently, several experimental efforts were made to measure PBAP within marine environments [26][27][28] and in laboratory studies 29,30 combining UV-LIF methods with offline measurements such as lter collection. Other studies have also attempted to determine the role of seawater characteristics on the emission of PBAP.…”

Measurements of Aerosol Particle Size Distributions and INPs Over the Southern Ocean in the Late Austral Summer of 2017 on Board the R/V Mirai: Importance of the Marine Boundary Layer Structure

“…FAPs of type A (which are typically bacterial particles (∼1 μm) as suggested by Hernandez et al (2016)) dominated the identified types throughout the cruise (Figure 3c). Dominances of FAPs of type A in the MBL have also been found in previous studies (Kawana et al, 2021;Moallemi et al, 2021). Moallemi et al (2021) revealed that FAPs concentrations in the MBL positively correlated with bacteria (∼0.5-1 μm) and small-sized eukaryotic phytoplankton (∼1-3 μm) concentrations in surface seawater of the SO.…”

“…Dominances of FAPs of type A in the MBL have also been found in previous studies (Kawana et al, 2021;Moallemi et al, 2021). Moallemi et al (2021) revealed that FAPs concentrations in the MBL positively correlated with bacteria (∼0.5-1 μm) and small-sized eukaryotic phytoplankton (∼1-3 μm) concentrations in surface seawater of the SO. A bimodal PSD and a local minimum in the submicron size range between two modes were observed throughout the cruise (Figure 3b).…”

“…The number ratio of FAPs to coarse aerosol particles for 0.7-3.0 μm (CN WIBS ) measured using the WIBS, NR FL , was very low (∼0.6% on average) throughout the cruise and was weakly size-dependent (slightly higher for the larger diameter range, Figure 3b). Moallemi et al (2021) found the similar size distributions and NR FL of FAPs derived from the WIBS measurements in the circum-Antarctica cruise in the austral summer of 2017. They showed that NR FL increased as the diameter increases especially from ∼2 μm by the presence of relatively large bioaerosols (e.g., phytoplankton).…”