12 research outputs found
Water uptake of subpollen aerosol particles: Hygroscopic growth, cloud condensation nuclei activation, and liquid-liquid phase separation
Pollen grains emitted from vegetation can release subpollen particles (SPPs) that contribute to the fine fraction of atmospheric aerosols and may act as cloud condensation nuclei (CCN), ice nuclei (IN), or aeroallergens. Here, we investigate and characterize the hygroscopic growth and CCN activation of birch, pine, and rapeseed SPPs. A high-humidity tandem differential mobility analyzer (HHTDMA) was used to measure particle restructuring and water uptake over a wide range of relative humidity (RH) from 2â% to 99.5â%, and a continuous flow CCN counter was used for size-resolved measurements of CCN activation at supersaturations (S) in the range of 0.2â% to 1.2â%. For both subsaturated and supersaturated conditions, effective hygroscopicity parameters, Îș, were obtained by Köhler model calculations. Gravimetric and chemical analyses, electron microscopy, and dynamic light scattering measurements were performed to characterize further properties of SPPs from aqueous pollen extracts such as chemical composition (starch, proteins, DNA, and inorganic ions) and the hydrodynamic size distribution of water-insoluble material. All investigated SPP samples exhibited a sharp increase of water uptake and Îș above âŒ95â% RH, suggesting a liquidâliquid phase separation (LLPS). The HHTDMA measurements at RHâ>95â% enable closure between the CCN activation at water vapor supersaturation and hygroscopic growth at subsaturated conditions, which is often not achieved when hygroscopicity tandem differential mobility analyzer (HTDMA) measurements are performed at lower RH where the water uptake and effective hygroscopicity may be limited by the effects of LLPS. Such effects may be important not only for closure between hygroscopic growth and CCN activation but also for the chemical reactivity, allergenic potential, and related health effects of SPPs
EURECâŽA
The science guiding the EURECâŽA campaign and its measurements is presented. EURECâŽA comprised roughly 5 weeks of measurements in the downstream winter trades of the North Atlantic â eastward and southeastward of Barbados. Through its ability to characterize processes operating across a wide range of scales, EURECâŽA marked a turning point in our ability to observationally study factors influencing clouds in the trades, how they will respond to warming, and their link to other components of the earth system, such as upper-ocean processes or the life cycle of particulate matter. This characterization was made possible by thousands (2500) of sondes distributed to measure circulations on meso- (200âkm) and larger (500âkm) scales, roughly 400âh of flight time by four heavily instrumented research aircraft; four global-class research vessels; an advanced ground-based cloud observatory; scores of autonomous observing platforms operating in the upper ocean (nearly 10â000 profiles), lower atmosphere (continuous profiling), and along the airâsea interface; a network of water stable isotopologue measurements; targeted tasking of satellite remote sensing; and modeling with a new generation of weather and climate models. In addition to providing an outline of the novel measurements and their composition into a unified and coordinated campaign, the six distinct scientific facets that EURECâŽA explored â from North Brazil Current rings to turbulence-induced clustering of cloud droplets and its influence on warm-rain formation â are presented along with an overview of EURECâŽA's outreach activities, environmental impact, and guidelines for scientific practice. Track data for all platforms are standardized and accessible at https://doi.org/10.25326/165 (Stevens, 2021), and a film documenting the campaign is provided as a video supplement
EURECâŽA
The science guiding the EURECâŽA campaign and its measurements is presented. EURECâŽA comprised roughly 5 weeks of measurements in the downstream winter trades of the North Atlantic â eastward and southeastward of Barbados. Through its ability to characterize processes operating across a wide range of scales, EURECâŽA marked a turning point in our ability to observationally study factors influencing clouds in the trades, how they will respond to warming, and their link to other components of the earth system, such as upper-ocean processes or the life cycle of particulate matter. This characterization was made possible by thousands (2500) of sondes distributed to measure circulations on meso- (200âkm) and larger (500âkm) scales, roughly 400âh of flight time by four heavily instrumented research aircraft; four global-class research vessels; an advanced ground-based cloud observatory; scores of autonomous observing platforms operating in the upper ocean (nearly 10â000 profiles), lower atmosphere (continuous profiling), and along the airâsea interface; a network of water stable isotopologue measurements; targeted tasking of satellite remote sensing; and modeling with a new generation of weather and climate models. In addition to providing an outline of the novel measurements and their composition into a unified and coordinated campaign, the six distinct scientific facets that EURECâŽA explored â from North Brazil Current rings to turbulence-induced clustering of cloud droplets and its influence on warm-rain formation â are presented along with an overview of EURECâŽA's outreach activities, environmental impact, and guidelines for scientific practice. Track data for all platforms are standardized and accessible at https://doi.org/10.25326/165 (Stevens, 2021), and a film documenting the campaign is provided as a video supplement
Water uptake of subpollen aerosol particles: hygroscopic growth, CCN activation, and liquid-liquid phase separation
Pollen grains emitted from vegetation can release subpollen particles (SPP) that contribute to the fine fraction of atmospheric aerosols and may act as cloud condensation nuclei (CCN), ice nuclei (IN), or aeroallergens. Here, we investigate and characterize the hygroscopic growth and CCN activation of birch, pine, and rapeseed SPP. A high humidity tandem differential mobility analyzer (HHTDMA) was used to measure particle restructuring and water uptake over a wide range of relative humidity (RH) from 2â% to 99.5â%, and a continuous flow CCN counter was used for size-resolved measurements of CCN activation at supersaturations (S) in the range of 0.2â% to 1.2â%. For both, subsaturated and supersaturated conditions, effective hygroscopicity parameters Îș, were obtained by Köhler model calculations. Gravimetric and chemical analyses, electron microscopy, and dynamic light scattering measurements were performed to characterize further properties of SPP from aqueous pollen extracts such as chemical composition (starch, proteins, DNA, and inorganic ions) and the hydrodynamic size distribution of water-insoluble material. All investigated SPP samples exhibited sharp increases of water uptake and Îș above ~95â% RH, suggesting a liquid-liquid phase separation (LLPS). The HHTDMA measurements at RHâ>â95â% enable closure between the CCN activation at water vapor supersaturation and hygroscopic growth at subsaturated conditions, which is often not achieved when HTDMA measurements are performed at lower RH where the water uptake and effective hygroscopicity may be limited by the effects of LLPS. Such effects may be important not only for closure between hygroscopic growth and CCN activation but also for the chemical reactivity, allergenic potential, and related health effects of SPPs
Water uptake of subpollen aerosol particles: hygroscopic growth, CCN activation, and liquid-liquid phase separation
Pollen grains emitted from vegetation can release subpollen particles (SPP) that contribute to the fine fraction of atmospheric aerosols and may act as cloud condensation nuclei (CCN), ice nuclei (IN), or aeroallergens. Here, we investigate and characterize the hygroscopic growth and CCN activation of birch, pine, and rapeseed SPP. A high humidity tandem differential mobility analyzer (HHTDMA) was used to measure particle restructuring and water uptake over a wide range of relative humidity (RH) from 2â% to 99.5â%, and a continuous flow CCN counter was used for size-resolved measurements of CCN activation at supersaturations (S) in the range of 0.2â% to 1.2â%. For both, subsaturated and supersaturated conditions, effective hygroscopicity parameters Îș, were obtained by Köhler model calculations. Gravimetric and chemical analyses, electron microscopy, and dynamic light scattering measurements were performed to characterize further properties of SPP from aqueous pollen extracts such as chemical composition (starch, proteins, DNA, and inorganic ions) and the hydrodynamic size distribution of water-insoluble material. All investigated SPP samples exhibited sharp increases of water uptake and Îș above ~95â% RH, suggesting a liquid-liquid phase separation (LLPS). The HHTDMA measurements at RHâ>â95â% enable closure between the CCN activation at water vapor supersaturation and hygroscopic growth at subsaturated conditions, which is often not achieved when HTDMA measurements are performed at lower RH where the water uptake and effective hygroscopicity may be limited by the effects of LLPS. Such effects may be important not only for closure between hygroscopic growth and CCN activation but also for the chemical reactivity, allergenic potential, and related health effects of SPP
Satellite-based detection of secondary droplet activation in convective clouds
We present a new approach of analyzing and interpreting vertical profiles of cloud microstructure obtained by satellite remote sensing. The method is based on a spectral bin microphysics adiabatic parcel model and aims to elucidate the effects of aerosols on the evolution of convective clouds and related microphysical processes, including the activation of cloud condensation nuclei (CCN), the growth of cloud droplets, and the formation of precipitation. Characteristic features in the vertical profiles of effective radius (re) and temperature (T) reveal different microphysical zones in convective clouds related to the change increase of re with decreasing T. The classification of the different microphysical zones includes the (1) condensational growth of droplets, (2) growth by coalescence, (3) rainout, (4) secondary droplet activation zone (SAZ), (5) mixed-phase of ice particles and water droplets and (6) glaciation of the cloud. The detection of the SAZ is introduced here for the first time. This method allows us to identify the activation of aerosol particles above cloud base and their role in the invigoration of deep convective clouds
Occurrence and growth of sub-50ânm aerosol particles in the Amazonian boundary layer
New particle formation (NPF), referring to the nucleation of molecular clusters and their subsequent growth into the cloud condensation nuclei (CCN) size range, is a globally significant and climate-relevant source of atmospheric aerosols. Classical NPF exhibiting continuous growth from a few nanometers to the Aitken mode around 60â70ânm is widely observed in the planetary boundary layer (PBL) around the world, but not in central Amazonia. Here, classical NPF events are rarely observed in the PBL, but instead, NPF begins in the upper troposphere (UT), followed by downdraft injection of sub-50ânm (CN<â50) particles into the PBL and their subsequent growth. Central aspects of our understanding of these processes in the Amazon have remained enigmatic, however. Based on more than six years of aerosol and meteorological data from the Amazon Tall Tower Observatory (ATTO, Feb 2014 to Sep 2020), we analyzed the diurnal and seasonal patterns as well as meteorological conditions during 254 of such Amazonian growth events on 217 event days, which show a sudden occurrence of particles between 10 and 50ânm in the PBL, followed by their growth to CCN sizes. The occurrence of events was significantly higher during the wet season, with 88â% of all events from January to June, than during the dry season, with 12â% from July to December, probably due to differences in the condensation sink (CS), atmospheric aerosol load, and meteorological conditions. Across all events, a median growth rate (GR) of 5.2ânmâhâ1 and a median CS of 0.0011âsâ1 were observed. The growth events were more frequent during the daytime (74â%) and showed higher GR (5.9ânmâhâ1) compared to nighttime events (4.0ânmâhâ1), emphasizing the role of photochemistry and PBL evolution in particle growth. About 70â% of the events showed a negative anomaly of the equivalent potential temperature (âΞ'e) â as a marker for downdrafts â and a low satellite brightness temperature (Tir) â as a marker for deep convective clouds â in good agreement with particle injection from the UT in the course of strong convective activity. About 30â% of the events, however, occurred in the absence of deep convection, partly under clear sky conditions, and with a positive âΞ'e anomaly. Therefore, these events do not appear to be related to downdraft injection and suggest the existence of other currently unknown sources of the sub-50ânm particles
Occurrence and growth of sub-50ânm aerosol particles in the Amazonian boundary layer
New particle formation (NPF), referring to the nucleation of molecular clusters and their subsequent growth into the cloud condensation nuclei (CCN) size range, is a globally significant and climate-relevant source of atmospheric aerosols. Classical NPF exhibiting continuous growth from a few nanometers to the Aitken mode around 60â70ânm is widely observed in the planetary boundary layer (PBL) around the world but not in central Amazonia. Here, classical NPF events are rarely observed within the PBL, but instead, NPF begins in the upper troposphere (UT), followed by downdraft injection of sub-50ânm (CN<50) particles into the PBL and their subsequent growth. Central aspects of our understanding of these processes in the Amazon have remained enigmatic, however. Based on more than 6 years of aerosol and meteorological data from the Amazon Tall Tower Observatory (ATTO; February 2014 to September 2020), we analyzed the diurnal and seasonal patterns as well as meteorological conditions during 254 of such Amazonian growth events on 217 event days, which show a sudden occurrence of particles between 10 and 50ânm in the PBL, followed by their growth to CCN sizes. The occurrence of events was significantly higher during the wet season, with 88â% of all events from January to June, than during the dry season, with 12â% from July to December, probably due to differences in the condensation sink (CS), atmospheric aerosol load, and meteorological conditions. Across all events, a median growth rate (GR) of 5.2ânmâhâ1 and a median CS of 1.1âĂâ10â3âsâ1 were observed. The growth events were more frequent during the daytime (74â%) and showed higher GR (5.9ânmâhâ1) compared to nighttime events (4.0ânmâhâ1), emphasizing the role of photochemistry and PBL evolution in particle growth. About 70â% of the events showed a negative anomaly of the equivalent potential temperature () â as a marker for downdrafts â and a low satellite brightness temperature (Tir) â as a marker for deep convective clouds â in good agreement with particle injection from the UT in the course of strong convective activity. About 30â% of the events, however, occurred in the absence of deep convection, partly under clear-sky conditions, and with a positive anomaly. Therefore, these events do not appear to be related to downdraft transport and suggest the existence of other currently unknown sources of sub-50ânm particles
African biomass burning affects aerosol cycling over the Amazon
Abstract Smoke from vegetation fires affects air quality, atmospheric cycling, and the climate in the Amazon rain forest. A major unknown has remained the quantity of long-range transported smoke from Africa in relation to local and regional fire emissions. Here we quantify the abundance, seasonality, and properties of African smoke in central Amazonia. We show that it accounts for ~â60% of the black carbon concentrations during the wet season and ~â30% during the dry season. The African smoke influences aerosol-radiation interactions across the entire Amazon, with the strongest impact on the vulnerable eastern basin, a hot spot of climate and land use change. Our findings further suggest that the direct influence of African smoke has been historically relevant for soil fertilization, the carbon and water cycles, and, thus, the development of the Amazon forest ecosystem, even in the pre-industrial era
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African biomass burning affects aerosol cycling over the Amazon
AbstractSmoke from vegetation fires affects air quality, atmospheric cycling, and the climate in the Amazon rain forest. A major unknown has remained the quantity of long-range transported smoke from Africa in relation to local and regional fire emissions. Here we quantify the abundance, seasonality, and properties of African smoke in central Amazonia. We show that it accounts for ~â60% of the black carbon concentrations during the wet season and ~â30% during the dry season. The African smoke influences aerosol-radiation interactions across the entire Amazon, with the strongest impact on the vulnerable eastern basin, a hot spot of climate and land use change. Our findings further suggest that the direct influence of African smoke has been historically relevant for soil fertilization, the carbon and water cycles, and, thus, the development of the Amazon forest ecosystem, even in the pre-industrial era