25 research outputs found
Exploring the relationship between relative humidity and aerosol attenuated backscatter ratio: Geoscience & Remote Sensing
No full textClouds and aerosols continue to contribute to the largest uncertainty to estimates and interpretations of the Earth's changing energy budget. By comparing relative humidity (RH) and attenuated backscatter ratio (ATB) data and deriving scattering hygroscopic enhancement factors at the Cabauw Experimental Site for Atmospheric Physics Research (CESAR), an attempt is made to better understand the process of aerosol hygroscopic growth. This is done by ground based ceilometer, hygrometer and SMPS technology gathering data during the ACCEPT campaign in 2014, resulting in a high temporal resolution, continuous measurements and the possibility to compare the data with ancillary information measured on the same location. Some aerosol number concentration (ANC) data is also taken into account as indication of the influence of ANC on ATB. For the three studied time intervals with a large variation (>30%) in RH, a convincing relation between RH and ATB is found, which can be linked to the Köhler curve when a direct relation between aerosol size and ATB is assumed. For these three time intervals, scattering hygroscopic enhancement factors are derived with similar γ values as reported in previous studies. Further research is required to analyze the correlation between RH and ATB more and rule out other influences on ATB.Civil Engineerin
Field Observations of Atmospheric Aerosol Properties and the Impacts of New Particle Formation on the Radiative Properties of Clouds
No full textAtmospheric aerosol particles are solid or liquid particles suspended in the atmosphere. They are directly emitted into the atmosphere or they are formed via the oxidation of gaseous precursors. Understanding the behavior of particles in the atmosphere is particularly important because they can affect the Earth’s climate, visibility, air quality, human health, and the ecosystem. As a result, they are a topic of high interest for the scientific community...Atmospheric Remote Sensin
Researcher’s guilt:confessions from the darker side of ethnographic consumer research
No full textA reflexive approach to qualitative research seeks to uncover structures of inequality in the research encounter. On the surface, it would seem that ethnographic methods provide the conditions to alleviate this methodological instrumentalism. By employing a confessional account, this paper demonstrates how the paradox of asymmetrical rapport prevents ethnographic work from reaching its collaborative potential. Drawing from insights in an ethnographic enquiry in an arts charity, the author narrates the guilty experiences that arise when researchers reproduce a culture of commodifying informants. This is exemplified through impression management tactics that generate an illusion of mutuality, alternating with more authentic instances of co-participation. The implications of this self-perceived moral violation are discussed for the researched, the researcher and ethnographies of consumption more broadly. The paper contributes to the methodological literature by explaining the potential of confessional accounts as a tool to operationalise reflexive, reciprocal practice, counteracting the demands of a knowledge economy.</p
Determination of aerosol optical properties with lidar: A comparison between algorithms
No full textLidar systems can provide vertically resolved measurements of the physical and optical properties of the atmospheric particles with high spatiotemporal resolution. In this study, four case studies were analyzed and studied in order to identify the dominant aerosol type over the city of Nicosia in Cyprus: 05 April and 07 April 2015 and 17 April and 21 April 2016. More specifically, vertical profiles of the extinction and backscatter coefficient, Ångström exponent, particle linear depolarization ratio and lidar ratio were manually retrieved from the lidar signal for each case study. For the first case, the main aerosol load was observed in the very lower atmosphere, between 0.25 and 1.25 km. The observed aerosol optical properties indicated the strong presence of maritime aerosols. In the second case study, the aerosol layer was thicker and it was observed between 1.6 and 7 km. Analysis of the optical properties showed that the predominant aerosol types within the PBL were mainly maritime aerosols and aerosols from local sources while higher in the atmosphere the aerosol load consisted of dust mixtures. The third case study, on 17th April 2016, was a relatively clean day and a thin aerosol layer was observed between 0.25 and 2.0 km consisting mainly of maritime and urban aerosols. 21st of April 2016, which was the fourth case study, was a dust event case study. The aerosol load, accumulated between 2.0 and 5.0 km, was characterized as a purely dust layer. The results obtained with the manual retrieval method, were compared with automatically retrieved profiles (provided by the Leibniz Institute for Tropospheric Research) and are in good agreement. More specifically, for the vertically resolved extinction profiles at 532 nm the correlation coefficient values ranged between 0.9784 and 1. The correlation coefficients for the backscatter profiles at 532 nm and 1064 nm ranged from 0.9975 to 0.9986 and from 0.9937 to 0.9996 respectively. The linear particle depolarization ratio profiles also correlated less well with the automatically retrieved one with R ranging from 0.8781 to 0.9889 while similarly, for the volume depolarization ratio profiles the correlation coefficient ranged between 0.7054 to 0.9603
Vertical profiles of aerosol mass concentration derived by unmanned airborne in situ and remote sensing instruments during dust events
No full textIn situ measurements using unmanned aerial vehicles (UAVs) and remote sensing observations can independently provide dense vertically resolved measurements of atmospheric aerosols, information which is strongly required in climate models. In both cases, inverting the recorded signals to useful information requires assumptions and constraints, and this can make the comparison of the results difficult. Here we compare, for the first time, vertical profiles of the aerosol mass concentration derived from light detection and ranging (lidar) observations and in situ measurements using an optical particle counter on board a UAV during moderate and weak Saharan dust episodes. Agreement between the two measurement methods was within experimental uncertainty for the coarse mode (i.e. particles having radii &gt; 0.5ĝ€μm), where the properties of dust particles can be assumed with good accuracy. This result proves that the two techniques can be used interchangeably for determining the vertical profiles of aerosol concentrations, bringing them a step closer towards their systematic exploitation in climate models.Atmospheric Remote SensingGeoscience and Remote Sensin
Application of Cabauw Lidar Data for Campaigns, New Methodology Development and Satellite Validation Activities
No full textCabauw lidar data were used for the development of several new methods, as well as in the validation of new techniques based on other sensor data. The potential of the site that is equipped with a suite of in-situ and remote sensing equipment provides the possibility to develop new methods, and test them using independent observations.
Examples are shown for several recent campaigns conducted at the site, new methods developed using lidar data, and for satellite validation, including preparation for future missions
Retrieval of ice-nucleating particle concentrations from lidar observations and comparison with UAV in situ measurements
No full textAerosols that are efficient ice-nucleating particles (INPs) are crucial for the formation of cloud ice via heterogeneous nucleation in the atmosphere. The distribution of INPs on a large spatial scale and as a function of height determines their impact on clouds and climate. However, in situ measurements of INPs provide sparse coverage over space and time. A promising approach to address this gap is to retrieve INP concentration profiles by combining particle concentration profiles derived by lidar measurements with INP efficiency parameterizations for different freezing mechanisms (immersion freezing, deposition nucleation). Here, we assess the feasibility of this new method for both ground-based and spaceborne lidar measurements, using in situ observations collected with unmanned aerial vehicles (UAVs) and subsequently analyzed with the FRIDGE (FRankfurt Ice nucleation Deposition freezinG Experiment) INP counter from an experimental campaign at Cyprus in April 2016. Analyzing five case studies we calculated the cloud-relevant particle number concentrations using lidar measurements (n250,dry with an uncertainty of 20 % to 40 % and Sdry with an uncertainty of 30 % to 50 %), and we assessed the suitability of the different INP parameterizations with respect to the temperature range and the type of particles considered. Specifically, our analysis suggests that our calculations using the parameterization of Ullrich et al. (2017) (applicable for the temperature range −50 to −33 ∘C) agree within 1 order of magnitude with the in situ observations of nINP; thus, the parameterization of Ullrich et al. (2017) can efficiently address the deposition nucleation pathway in dust-dominated environments. Additionally, our calculations using the combination of the parameterizations of DeMott et al. (2015, 2010) (applicable for the temperature range −35 to −9 ∘C) agree within 2 orders of magnitude with the in situ observations of INP concentrations (nINP) and can thus efficiently address the immersion/condensation pathway of dust and nondust particles. The same conclusion is derived from the compilation of the parameterizations of DeMott et al. (2015) for dust and Ullrich et al. (2017) for soot.Atmospheric Remote Sensin
Long-term observations of the background aerosol at Cabauw, The Netherlands.
No full textLong-term measurements of PM2.5 mass concentrations and aerosol particle size distributions from 2008 to 2015, as well as hygroscopicity measurements conducted over one year (2008-2009) at Cabauw, The Netherlands, are compiled here in order to provide a comprehensive dataset for understanding the trends and annual variabilities of the atmospheric aerosol in the region. PM2.5 concentrations have a mean value of 14.4μgm-3 with standard deviation 2.1μgm-3, and exhibit an overall decreasing trend of -0.74μgm-3year-1. The highest values are observed in winter and spring and are associated with a shallower boundary layer and lower precipitation, respectively, compared to the rest of the seasons. Number concentrations of particles smaller than 500nm have a mean of 9.2×103particles cm-3 and standard deviation 4.9×103particles cm-3, exhibiting an increasing trend between 2008 and 2011 and a decreasing trend from 2013 to 2015. The particle number concentrations exhibit highest values in spring and summer (despite the increased precipitation) due to the high occurrence of nucleation-mode particles, which most likely are formed elsewhere and are transported to the observation station. Particle hygroscopicity measurements show that, independently of the air mass origin, the particles are mostly externally mixed with the more hydrophobic mode having a mean hygroscopic parameter κ of 0.1 while for the more hydrophilic mode κ is 0.35. The hygroscopicity of the smaller particles investigated in this work (i.e., particles having diameters of 35nm) appears to increase during the course of the nucleation events, reflecting a change in the chemical composition of the particles
