Abstract
Abstract. Due to low concentrations and chemical complexity, in situ observations of bioaerosol are geographically and temporally sparse, and this limits the accuracy of current emissions inventories. In this study, we apply a new methodology, including corrections for misidentification of mineral dust, to measurements of single particles over four airborne sampling campaigns to derive vertical profiles of bioaerosol over the continental United States. The new methodology is based on single-particle mass spectrometry (SPMS); it can extend historic datasets to include measurements of bioaerosol, it allows comparisons to other techniques, and it generally agrees with a global aerosol model. In the locations sampled, bioaerosols were at least a factor of 10 less abundant than mineral dust. Below 2 km, bioaerosol concentrations were measured between 6×103 and 2×104 m−3. Between 2 and 8 km, bioaerosol concentrations were between 0 and 2×104 m−3, and above 8 km, bioaerosol concentrations were between 0 and 1×103 m−3. Between 30 % and 80 % of single bioaerosol particles detected were internally mixed with dust. A direct comparison of the SPMS methodology with a co-located wideband integrated bioaerosol sensor (WIB) fluorescence sensor on a mountaintop site showed agreement to within a factor of 3 over the common size range.
Highlights
The effects of aerosols, clouds, and their mutual interactions on the climate system are more uncertain than those of greenhouse gases (Boucher et al, 2013)
Bioaerosol can act as efficient cloud condensation nuclei (CCN) and, because certain bacteria have been shown to be efficient ice nucleating particles (INPs) in laboratory studies (Möhler et al, 2008), it has been proposed that bioaerosol could play a significant role in atmospheric ice nucleation (Möhler et al, 2007)
A more detailed investigation matching the meteorological year and the size range measured could help provide quantitative insights into the deficiencies in the model description of bioaerosol emissions, removal, and vertical transport by convection, and we suggest this is as possible future work
Summary
The effects of aerosols, clouds, and their mutual interactions on the climate system are more uncertain than those of greenhouse gases (Boucher et al, 2013). Aerosols can influence Earth’s radiative budget both directly, by scattering and absorbing incoming solar radiation, and indirectly, by nucleating clouds. Clouds can scatter solar radiation and trap terrestrial heat with a balance that depends on their specific properties (Boucher et al, 2013). Bioaerosol can act as efficient CCN and, because certain bacteria have been shown to be efficient INPs in laboratory studies (Möhler et al, 2008), it has been proposed that bioaerosol could play a significant role in atmospheric ice nucleation (Möhler et al, 2007). Real-time and in situ measurements of atmospheric ice nuclei are scarce, which makes it difficult to directly observe and quantify this effect (Cziczo et al, 2013; Ebert et al, 2011).
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