104 research outputs found
Microphysical properties of aerosol particles in the trade wind regime and their influence on the number concentration of activated particles in trade wind cumulus clouds
Im Rahmen dieser Dissertation wurden die mikrophysikalischen Eigenschaften von Aerosolpartikeln im Passatklima und deren Einfluss auf Passatwolken untersucht. Die Arbeit basiert auf Messungen mit der hubschrauber-getragenen Messplattform ACTOS. Es wurden zwei Intensivmesskampagnen im November 2010 und April 2011 durchgefĂŒhrt, welche 31 ForschungsflĂŒge in der NĂ€he der östlichsten Karibik-Insel Barbados umfassen.
Die gemessenen Partikel-Anzahl-GröĂenverteilungen weisen meist eine bimodale Verteilung auf, welche typisch fĂŒr marines Aerosol ist. Im Vergleich zu kontinentalen VerhĂ€ltnissen ist die Totalanzahlkonzentration der Aerosolpartikel von 100-1000 cm-3 gering. Eine statistische Analyse einzelner Wolken lĂ€sst auf typische Anzahlkonzentrationen von aktivierten Partikeln bis zu 400 cm-3 und minimale
Aktivierungsdurchmesser in der GröĂenordnung von 40 nm bis 180 nm mit entsprechenden maximalen kritischen ĂbersĂ€ttigungen zwischen 0.1 und 0.9% schlieĂen. ZusĂ€tzlich wurden wesentliche Einflussfaktoren auf die Anzahlkonzentration aktivierter Partikel identifiziert: 1) Vertikalwind an
der Wolkenunterkante und 2) Anzahlkonzentration der verfĂŒgbaren Aerosolpartikel, die als Wolkenkondensationskeime dienen können.
Mit Hilfe von Beobachtungsdaten und einer umfassenden SensitivitĂ€tsstudie unter Verwendung eines Luftpaketmodells mit spektraler Wolkenmikrophysik wurde die SensitivitĂ€t der Wolkentropfenkonzentration gegenĂŒber Ănderungen in den physikalischen Eigenschaften und der HygroskopizitĂ€t von
Aerosolpartikeln untersucht. Die beobachteten Ergebnisse in Form von sogenannten \"aerosol-cloud interaction metrics\" (ACI, MaĂ fĂŒr den Einfluss von Ănderungen einer bestimmten Aerosoleigenschaft auf eine bestimmte Wolkeneigenschaft) zeigen eine sehr hohe SensitivitĂ€t der Tropfenanzahlkonzentration
gegenĂŒber Ănderungen in der Partikelanzahlkonzentration (in der NĂ€he des physikalisch sinnvollen Maximums von eins). Diese abgeleiteten ACI-Metriken eignen sich als Basis fĂŒr AbschĂ€tzungen des indirekten Strahlungsantriebes auf der Grundlage von Beobachtungen.
ZusÀtzliche Modellrechnungen umfassen die gemessenen Partikeleigenschaften wÀhrend der gesamten Kampagnen. Die Ergebnisse unterstreichen besonders die Bedeutung der physikalischen Partikeleigenschaften.
Die SuszeptibilitĂ€t der Tropfenanzahlkonzentration gegenĂŒber Ănderungen in der Partikelanzahlkonzentration (Wertebereich: 0-1) ist am gröĂten (> 0.9) fĂŒr den Fall eines stark ausgeprĂ€gten Akkumulations-Mode und nimmt ab, je stĂ€rker der Aitken-Mode ausgeprĂ€gt ist (> 0.6). Im Gegensatz dazu ist die SensitivitĂ€t der Tropfenanzahlkonzentration gegenĂŒber Ănderungen in der
HygroskopizitĂ€t der Partikel generell geringer (< 0.4). Die hier prĂ€sentierten Ergebnisse stellen eine umfangreiche Charakterisierung der Aerosol- und Wolkeneigenschaften im Passatklima dar und können helfen, die vorhergesagte SensitivitĂ€t der Wolkeneigenschaften in Klimamodellen gegenĂŒber
Ănderungen der Aerosoleigenschaften zu evaluieren und deren Unsicherheiten zu reduzieren.Within the scope of this dissertation, microphysical properties of aerosol particles in the trade wind regime and their influence on microphysical properties of trade wind cumulus clouds have been investigated.
The study is based on measurements performed with the helicopter-borne measurement platform ACTOS. Two intensive measurement periods were carried out in November 2010 and April 2011, including 31 research flights close to the easternmost Caribbean island - Barbados.
Aerosol particle number size distributions show a bimodal structure, which is typical for marine aerosol particles. The total particle concentrations of approximately 100-1000 cm-3 are compared to continental conditions relatively low. A statistical analysis of individual clouds reveals typical number concentrations of activated particles up to 400 cm-3 and minimum activation diameters between 40 and
180 nm with corresponding critical supersaturations between 0.1 and 1%. Additionally, major factors affecting the number concentration of activated particles are identifed: 1) vertical wind velocity at cloud base and, 2) number concentration of available aerosol particles as potential cloud condensation nuclei.
With the help of observational data and a comprehensive sensitivity study using a spectral cloud microphysical parcel model, the sensitivity of the cloud droplet number concentration towards changes in the microphysical aerosol particle properties and their hygroscopicity has been investigated.
Observational results in terms of so-called aerosol-cloud interactions metrics (describes a measure of the influence of changes in one specific aerosol property on one specific cloud property) show a very high sensitivity (close to the physical meaningful maximum of unity) of the number concentration of activated particles towards changes in the particle number concentration. These aerosol-cloud
interaction metrics can be used as basis for observationally-based radiative forcing estimates.
Additional model calculations cover the entire range of the observed aerosol properties during both campaigns. The results underline particularly the importance of the physical aerosol properties. The calculated susceptibility (valuation: 0-1) of the droplet number concentration towards changes in the particle number concentration is highest (> 0.9) for accumulation mode dominated particle number size distributions and decreases for Aitken mode dominated size distributions (> 0.6). In contrast, for the modeled parameter space, the sensitivity towards changes in the particle hygroscopicity is generally below 0.4.
The findings presented in this study represent a comprehensive characterization of aerosol and cloud microphysical properties in the trade wind regime. These findings may help to evaluate the predicted sensitivity of cloud microphysical properties by climate models towards changes in particle microphysical properties and reduce the uncertainties in climate sensitivity estimates
Characterisation of a new Fast CPC and its application for atmospheric particle measurements
A new Fast CPC (FCPC) using butanol as working fluid has been built based on the setup described by Wang et al. (2002). In this study, we describe the new instrument. The functionality and stable operation of the FCPC in the laboratory, as well as under atmospheric conditions, is demonstrated. The counting efficiency was measured for three temperature differences between FCPC saturator and condenser, 25, 27, and 29 K, subsequently resulting in a lower detection limit between 6.1 and 8.5 nm. Above 25 nm the FCPC reached 98â100% counting efficiency compared to an electrometer used as the reference instrument. The FCPC demonstrated its ability to perform continuous measurements over a few hours in the laboratory with respect to the total particle counting. The instrument has been implemented into the airborne measurement platform ACTOS to perform measurements in the atmospheric boundary layer. Therefore, a stable operation over two hours is required. The mixing time of the new FCPC was estimated in two ways using a time series with highly fluctuating particle number concentrations. The analysis of a sharp ramp due to a concentration change results in a mixing time of 5 ms while a spectral analysis of atmospheric data demonstrates that for frequencies up to 10 Hz coherent structures can be resolved before sampling noise dominates
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Aerosols-cloud microphysics-thermodynamics-turbulence: Evaluating supersaturation in a marine stratocumulus cloud
This work presents a unique combination of aerosol, cloud microphysical, thermodynamic and turbulence variables to characterize supersaturation fluctuations in a turbulent marine stratocumulus (SC) layer. The analysis is based on observations with the helicopter-borne measurement platform ACTOS and a detailed cloud microphysical parcel model following three different approaches: (1) From the comparison of aerosol number size distributions inside and below the SC layer, the number of activated particles is calculated as 435±87 cmâ3 and compares well with the observed median droplet number concentration of Nd = 464 cmâ3. Furthermore, a 50% activation diameter of Dp50â115 nm was derived, which was linked to a critical supersaturation Scrit of 0.16% via Köhler theory. From the shape of the fraction of activated particles, we estimated a standard deviation of supersaturation fluctuations of ÏS' = 0.09%. (2) These estimates are compared to more direct thermodynamic observations at cloud base. Therefore, supersaturation fluctuations (S') are calculated based on highly-resolved thermodynamic data showing a standard deviation of S' ranging within 0.1%â€ÏS'â€0.3 %. (3) The sensitivity of the supersaturation on observed vertical wind velocity fluctuations is investigated with the help of a detailed cloud microphysical model. These results show highest fluctuations of S' with ÏS'=0.1% at cloud base and a decreasing ÏS' with increasing liquid water content and droplet number concentration. All three approaches are independent of each other and vary only within a factor of about two
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Infrequent new particle formation over the remote boreal forest of Siberia
Aerosol particle number size distributions (PNSD) were investigated to verify, if extremely low-volatility organic vapors (ELVOC) from natural sources alone could induce new particle formation and growth events over the remote boreal forest region of Siberia, hundreds of kilometers away from significant anthropogenic sources. We re-evaluated observations determined at a height of 300 m of the remote observatory ZOTTO (Zotino Tall Tower Observatory, http://www.zottoproject.org). We found that new particle formation events occurred only on 11 days in a 3-year period, suggesting that homogeneous nucleation with a subsequent condensational growth could not be the major process, maintaining the particle number concentration in the planetary boundary layer of the remote boreal forest area of Siberia. © 2018 Elsevier Lt
Aerosols-cloud microphysics-thermodynamics-turbulence: Evaluating supersaturation in a marine stratocumulus cloud
This work presents a unique combination of aerosol, cloud microphysical, thermodynamic and turbulence variables to characterize supersaturation fluctuations in a turbulent marine stratocumulus (SC) layer. The analysis is based on observations with the helicopter-borne measurement platform ACTOS and a detailed cloud microphysical parcel model following three different approaches: (1) From the comparison of aerosol number size distributions inside and below the SC layer, the number of activated particles is calculated as 435 ± 87 cm -3 and compares well with the observed median droplet number concentration of NÌ d = 464 cm -3. Furthermore, a 50% activation diameter of D p50 â 115 nm was derived, which was linked to a critical supersaturation S crit of 0.16% via Köhler theory. From the shape of the fraction of activated particles, we estimated a standard deviation of supersaturation fluctuations of Ï SâČ = 0.09 %. (2) These estimates are compared to more direct thermodynamic observations at cloud base. Therefore, supersaturation fluctuations (SâČ) are calculated based on highly-resolved thermodynamic data showing a standard deviation of SâČ ranging within 0.1%â€ Ï SâČ â€ 0.3 %. (3) The sensitivity of the supersaturation on observed vertical wind velocity fluctuations is investigated with the help of a detailed cloud microphysical model. These results show highest fluctuations of Ï SâČ with Ï SâČ =0.1% at cloud base and a decreasing ÏSâČ with increasing liquid water content and droplet number concentration. All three approaches are independent of each other and vary only within a factor of about two
Relationships between submicrometer particulate air pollution and air mass history in Beijing, China, 2004â2006
The Chinese capital Beijing is one of the global megacities where the effects of rapid economic growth have led to complex air pollution problems that are not well understood. In this study, ambient particle number size distributions in Beijing between 2004 and 2006 are analysed as a function of regional meteorological transport. An essential result is that the particle size distribution in Beijing depends to large extent on the history of the synoptic scale air masses. A first approach based on manual back trajectory classification yielded differences in particulate matter mass concentration by a factor of two between four different air mass categories, including three main wind directions plus the case of stagnant air masses. A back trajectory cluster analysis refined these results, yielding a total of six trajectory clusters. Besides the large scale wind direction, the transportation speed of an air mass was found to play an essential role on the PM concentrations in Beijing. Slow-moving air masses were shown to be associated with an effective accumulation of surface-based anthropogenic emissions due to both, an increased residence time over densely populated land, and their higher degree of vertical stability. For the six back trajectory clusters, differences in PM1 mass concentrations by a factor of 3.5, in the mean air mass speed by a factor of 6, and in atmospheric visibility by a factor of 4 were found. The main conclusion is that the air quality in Beijing is not only degraded by anthropogenic aerosol sources from within the megacity, but also by sources across the entire Northwest China plain depending on the meteorological situation
Multi-wavelength aerosol light absorption measurements in the Amazon rainforest
The most important light-absorbing aerosol is black carbon (BC), which is emitted by incomplete combustion of
fossil fuels and biomass. BC is considered the second anthropogenic contributor to global warming. Beyond BC,
other aerosols like some organics, dust, and primary biological aerosol particles are able to absorb radiation. In contrast to BC, the light absorption coefficient of these aerosols is wavelength dependent. Therefore, multi-wavelength
measurements become important in environments where BC is not the predominant light-absorbing aerosol like in
the Amazon. The Amazon Tall Tower Observatory (ATTO) site is located in the remote Amazon rainforest, one of
the most pristine continental sites in the world during the wet season. In the dry season, winds coming from the
southern hemisphere are loaded with biomass burning aerosol particles originated by farming-related deforestation. BC and aerosol number concentration data from the last two years indicate this is the most polluted period.
Two different techniques have been implemented to measure the light absorption at different wavelengths; one of
them is the 7-wavelengths Aethalometer, model AE30, an instrument that measures the light attenuation on a filter
substrate and requires multiple scattering and filter-loading corrections to retrieve the light absorption coefficient.
The other method is an offline technique, the Multi-Wavelength Absorbance Analysis (MWAA), which is able
to measure reflectance and absorbance by aerosols collected on a filter and, by means of a radiative model, can
retrieve the light absorption coefficient. Filters collected during May-September 2014, comprehending wet-to-dry
transition and most of the dry season, were analyzed. The results indicate that the Absorption \uc5ngstr\uf6m Exponent
(AAE), a parameter that is directly proportional to the wavelength dependence of the aerosol light absorption, is
close to 1.0 during the transition period and slightly decreases in the beginning of the dry season. However, during
strong biomass burning episodes in the dry season, the AAE increases significantly, and reaches values higher than
1.3, indicating the presence of wavelength dependent light-absorbing aerosols like organics (brown carbon). The
present study is a contribution to the understanding of the optical properties of light-absorbing aerosol particles
under pristine and biomass-burning conditions
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Nucleation of jet engine oil vapours is a large source of aviation-related ultrafine particles
Large airports are a major source of ultrafine particles, which spread across densely populated residential areas, affecting air quality and human health. Jet engine lubrication oils are detectable in aviation-related ultrafine particles, however, their role in particle formation and growth remains unclear. Here we show the volatility and new-particle-formation ability of a common synthetic jet oil, and the quantified oil fraction in ambient ultrafine particles downwind of Frankfurt International Airport, Germany. We find that the oil mass fraction is largest in the smallest particles (10-18 nm) with 21% on average. Combining ambient particle-phase concentration and volatility of the jet oil compounds, we determine a lower-limit saturation ratio larger than 1 Ă 105 for ultra-low volatility organic compounds. This indicates that the oil is an efficient nucleation agent. Our results demonstrate that jet oil nucleation is an important mechanism that can explain the abundant observations of high number concentrations of non-refractory ultrafine particles near airports
How weather events modify aerosol particle size distributions in the Amazon boundary layer
This study evaluates the effect of weather events on the aerosol particle size distribution (PSD) at the Amazon Tall Tower Observatory (ATTO). This research combines in situ measurements of PSD and remote sensing data of lightning density, brightness temperature, cloud top height, cloud liquid water, and rain rate and vertical velocity. Measurements were obtained by scanning mobility particle sizers (SMPSs), the new generation of GOES satellites (GOES-16), the SIPAM S-band radar and the LAP 3000 radar wind profiler recently installed at the ATTO-Campina site. The combined data allow exploring changes in PSD due to different meteorological processes. The average diurnal cycle shows a higher abundance of ultrafine particles (NUFP) in the early morning, which is coupled with relatively lower concentrations in Aitken (NAIT) and accumulation (NACC) mode particles. From the early morning to the middle of the afternoon, an inverse behavior is observed, where NUFP decreases and NAIT and NACC increase, reflecting a typical particle growth process. Composite figures show an increase of NUFP before, during and after lightning was detected by the satellite above ATTO. These findings strongly indicate a close relationship between vertical transport and deep convective clouds. Lightning density is connected to a large increase in NUFP, beginning approximately 100âmin before the maximum lightning density and reaching peak values around 200âmin later. In addition, the removal of NACC by convective transport was found. Both the increase in NUFP and the decrease in NACC appear in parallel with the increasing intensity of lightning activity. The NUFP increases exponentially with the thunderstorm intensity. In contrast, NAIT and NACC show a different behavior, decreasing from approximately 100âmin before the maximum lightning activity and reaching a minimum at the time of maximum lightning activity. The effect of cloud top height, cloud liquid water and rain rate shows the same behavior, but with different patterns between seasons. The convective processes do not occur continually but are probably modulated by gravity waves in the range of 1 to 5âh, creating a complex mechanism of interaction with a succession of updrafts and downdrafts, clouds, and clear-sky situations. The radar wind profiler measured the vertical distribution of the vertical velocity. These profiles show that downdrafts are mainly located below 10âkm, while aircraft observations during the ACRIDICONâCHUVA campaign had shown maximum concentrations of ultrafine particles mainly above 10âkm. Our study opens new scientific questions to be evaluated in order to understand the intricate physical and chemical mechanisms involved in the production of new particles in Amazonia.</p
Observations of turbulence-induced new particle formation in the residual layer
Aerosol particle measurements in the atmospheric boundary layer performed by a helicopter-borne measurement payload and by a lidar system from a case study during the IMPACT field campaign in Cabauw (NL) are presented. Layers of increased number concentrations of ultrafine particles were observed in the residual layer, indicating relatively recent new-particle formation. These layers were characterized by a sub-critical Richardson number and concomitant increased turbulence. Turbulent mixing is likely to lead to local supersaturation of possible precursor gases which are essential for new particle formation. Observed peaks in the number concentrations of ultrafine particles at ground level are connected to the new particle formation in the residual layer by boundary layer development and vertical mixing
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