Abstract
Abstract. Primary biological aerosol particles (PBAPs), such as bacteria, viruses, fungi, and pollen, represent a small fraction of the total aerosol burden. Based on process model studies, we identify trends in the relative importance of PBAP properties, e.g., number concentration, diameter, hygroscopicity, surface tension, and contact angle, for their aerosol–cloud interactions and optical properties. While the number concentration of PBAPs likely does not affect total cloud condensation nuclei (CCN) concentrations globally, small changes in the hygroscopicity of submicron PBAPs might affect their CCN ability and thus their inclusion into clouds. Given that PBAPs are highly efficient atmospheric ice nuclei (IN) at T > −10 ∘C, we suggest that small changes in their sizes or surface properties due to chemical, physical, or biological processing might translate into large impacts on ice initiation in clouds. Predicted differences in the direct interaction of PBAPs with radiation can be equally large between different species of the same PBAP type and among different PBAP types. Our study shows that not only variability of PBAP types but also their physical, chemical, and biological ageing processes might alter their CCN and IN activities to affect their aerosol–cloud interactions and optical properties. While these properties and processes likely affect radiative forcing only on small spatial and temporal scales, we highlight their potential importance for PBAP survival, dispersion, and transport in the atmosphere.
Highlights
Primary biological aerosol particles (PBAPs) contribute a small fraction (50 Tg yr−1, with an upper limit of 1000 Tg yr−1) to the total natural global aerosol emissions of ∼ 2900–13 000 Tg yr−1 (Stocker et al, 2013), they have attracted great interest in the atmospheric science and public health communities as they might affect the climate and be responsible for spreading diseases (Asadi et al, 2020; Behzad et al, 2018; Khaled et al, 2021)
By means of process models (Sect. 3), we explore in a simplistic way the relative importance of these primary biological aerosol particles (PBAPs) properties and ageing processes for the effects depicted in Fig. 1
Experimental results show 1.528 ≤ n ≤ 1.576 and 0 ≤ k ≤ 0.02 for fresh secondary organic aerosols (SOAs) in the wavelength range of 0.3–0.56 μm; after nitration, the real part increases to 1.549 ≤ n ≤ 1.594 and the imaginary part increases to 0.0002 ≤ k ≤ 0.04 (Liu et al, 2015)
Summary
Primary biological aerosol particles (PBAPs) contribute a small fraction (50 Tg yr−1, with an upper limit of 1000 Tg yr−1) to the total natural global aerosol emissions of ∼ 2900–13 000 Tg yr−1 (Stocker et al, 2013), they have attracted great interest in the atmospheric science and public health communities as they might affect the climate and be responsible for spreading diseases (Asadi et al, 2020; Behzad et al, 2018; Khaled et al, 2021). Such processes are generally driven by strategies to adapt to the harsh conditions in the atmosphere (e.g., rapid temperature and RH changes, thaw–freeze cycles, humidification and desiccation, UV exposure) (Hamilton and Lenton, 1998; Horneck et al, 1994; Joly et al, 2015; Setlow, 2007) or to limit their atmospheric residence time by initiating precipitation (Hernandez and Lindow, 2019) These processes include nutrient uptake by biodegradation (Khaled et al, 2021); bacteria cell generation that enhances particle size and surface area (Ervens and Amato, 2020); formation of biofilms (extracellular polymeric substances), which enables PBAPs to form aggregates (Monier and Lindow, 2003, 2005; Morris et al, 2008; Sheng et al, 2010); expression of icenucleating proteins (Joly et al, 2013; Kjelleberg and Hermansson, 1984); formation of biosurfactants that enhances water uptake (Hernandez and Lindow, 2019; Neu, 1996); desiccation that decreases size of PBAPs (Barnard et al, 2013); formation of pigments (Pšencík et al, 2004; Fong et al, 2001) enhancing light absorption and fungal spore germination (Ayerst, 1969); formation of bacteria endospores (Enguita et al, 2003) that increases NPBAP; and the metabolism of cellular components (membranes, proteins, saccharides, osmolytes, etc.) (Fox and Howlett, 2008; Xie et al, 2010). We give some guidance on the need of future laboratory, field, and model studies to more accurately describe potential radiative effects, distribution, and residence time of PBAPs in the atmosphere
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