Bioaerosols and cloud formation
Biological aerosols, such as fungi, bacteria, algae, and pollen, are present everywhere in the atmosphere. But in different locations and under different atmospheric conditions, the types of bioaerosols and their concentration vary significantly. In clouds, bioaerosols can act as cloud condensation nuclei as well as ice nuclei and influence the hydrological cycle and climate.
However, there has been much uncertainty about the potential of various bioaerosol groups to facilitate precipitation through ice nucleation. Each bioaerosol group differs significantly in its ice nucleation activity. Currently, most of the information about the ice nucleation activity of bioaerosols is based on laboratory studies which may not represent the real atmosphere.
This is where Sachin Patade, Vaughan Phillips, and their colleagues come in. The purpose of the mission was to resolve the ice nucleation activity of the major bioaerosol groups by collecting samples directly from the atmosphere. A bioaerosol-rich atmosphere like the Amazon Rainforest makes the ATTO site an ideal place for their research.
The scientists collected bioaerosol samples at ATTO and analyzed them under Scanning Electron Microscope (SEM). From high-resolution SEM images of bioaerosols, they collected information about their types, sizes, and number concentrations. They also processed the collected bioaerosol samples in cloud chambers to estimate their ice nucleation activity. With this information, the team formulated an empirical parameterization where the ice nucleation activity of individual bioaerosol groups is a function of their total surface area present in the sampled air. Based on their analysis, the team formulated an empirical parameterization for five bioaerosol groups:
- Fungal spores and their fragments
- Bacteria and their fragments
- Pollen and their fragments
- Detritus of plants, animals and viruses
This new parameterization now makes it possible to resolve the ice nucleation activity of each bioaerosol group listed above in the numerical simulation of clouds. By implementing the proposed parameterization in cloud models, it is possible to investigate the role of each bioaerosol group on cloud properties and precipitation.
Patade et al. published their study “Empirical formulation for multiple groups of primary biological ice nucleating particles from field observations over Amazonia” in the Journal of the Atmospheric Sciences.
Biogenic volatile organic compounds remove OH from the atmosphere through chemical reactions, which affects processes such as cloud formation. In a new study, Pfannerstill et al. reveal the important contributions of previously not-considered BVOCs species and underestimated OVOCs to the total OH reactivity.
The majority of global precipitation is formed through the pathway of ice nucleation, but we’re facing large knowledge gaps that include the distribution, seasonal variations and sources of ice-nucleating particles. To fill some of those knowledge gaps, Jann Schrod and his co-authors produced a record of long-term measurements of INPs. They collected data for nearly two years at four different locations. One of those sites was ATTO.
Felipe Souza, Price Mathai and their co-authors published a new study analyzing the diverse bacterial population in the Amazonian atmosphere. The composition varied mainly with seasonal changes in temperature, relative humidity, and precipitation. On the other hand, they did not detect significant differences between the ground and canopy levels. They also identified bacterial species that participate in the nitrogen cycle.
Felipe Souza and co-authors now collected bioaerosols at our ATTO site. Then they extracted and analyzed the DNA to determine the communities present. This is the first study that described the community of microorganisms within aerosols in the Amazon. They found many different types of bacteria and fungi. Some were cosmopolitan taxa, but they also identified many that are specific to certain environments such as soil or water. This suggests that the atmosphere may act as an important gateway for bacteria to be exchanged between plants, soil, and water.
Mira Pöhlker and her team continuously measured aerosols and their properties in the atmosphere at the 80 m tower at ATTO, thereby created the first such long-term record in the Amazon. They analyzed the data in two subsequent paper. The second was now published in ACP.