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- ItemMALTE - Model to predict new aerosol formation in the lower troposphere(München : European Geopyhsical Union, 2006) Boy, M.; Hellmuth, O.; Korhonen, H.; Nilsson, E.D.; ReVelle, D.; Turnipseed, A.; Arnold, F.; Kulmala, M.The manuscript presents a detailed description of the meteorological and chemical code of Malte – a model to predict new aerosol formation in the lower troposphere. The aerosol dynamics are achieved by the new developed UHMA (University of Helsinki Multicomponent Aerosol Model) code with kinetic limited nucleation as responsible mechanism to form new clusters. First results indicate that the model is able to predict the on- and offset of new particle formation as well as the total aerosol number concentrations that were in good agreement with the observations. Further, comparison of predicted and measured H2SO4 concentrations showed a satisfactory agreement. The simulation results indicated that at a certain transitional particle diameter (2–7 nm), organic molecules can begin to contribute significantly to the growth rate compared to sulphuric acid. At even larger particle sizes, organic molecules can dominate the growth rate on days with significant monoterpene concentrations. The intraday vertical evolution of newly formed clusters and particles in two different size ranges resulted in two maxima at the ground. These particles grow around noon to the detectable size range and agree well with measured vertical profiles.
- ItemComparison of NLC particle sizes derived from SCIAMACHY/Envisat observations with ground-based LIDAR measurements at ALOMAR (69° N)(München : European Geopyhsical Union, 2009) von Savigny, C.; Robert, C.E.; Baumgarten, G.; Bovensmann, H.; Burrows, J.P.SCIAMACHY, the Scanning Imaging Absorption spectroMeter for Atmospheric CHartographY has provided measurements of limb-scattered solar radiation in the 220 nm to 2380 nm wavelength range since summer of 2002. Measurements in the UV spectral range are well suited for the retrieval of particle sizes of noctilucent clouds (NLCs) and have been used to compile the largest existing satellite data base of NLC particle sizes. This paper presents a comparison of SCIAMACHY NLC size retrievals with the extensive NLC particle size data set based on ground-based LIDAR measurements at the Arctic LIDAR Observatory for Middle Atmosphere Research (ALOMAR, 69° N, 16° E) for the Northern Hemisphere NLC seasons 2003 to 2007. Most of the presented SCIAMACHY NLC particle size retrievals are based on cylindrical particles and a Gaussian particle size distribution with a fixed width of 24 nm. If the differences in spatial as well as vertical resolution between SCIAMACHY and the ALOMAR LIDAR are taken into account, very good agreement is found. The mean particle size derived from SCIAMACHY limb observations for the ALOMAR overpasses in 2003 to 2007 is 56.2 nm with a standard deviation of 12.5 nm, and the LIDAR observations yield a value of 54.2 nm with a standard deviation of 17.4 nm.
- ItemA comprehensive laboratory study on the immersion freezing behavior of illite NX particles: A comparison of 17 ice nucleation measurement techniques(München : European Geopyhsical Union, 2015) Hiranuma, N.; Augustin-Bauditz, S.; Bingemer, H.; Budke, C.; Curtius, J.; Danielczok, A.; Diehl, K.; Dreischmeier, K.; Ebert, M.; Frank, F.; Hoffmann, N.; Kandler, K.; Kiselev, A.; Koop, T.; Leisner, T.; Möhler, O.; Nillius, B.; Peckhaus, A.; Rose, D.; Weinbruch, S.; Wex, H.; Boose, Y.; DeMott, P.J.; Hader, J.D.; Hill, T.C.J.; Kanji, Z.A.; Kulkarn, G.; Levin, E.J.T.; McCluskey, C.S.; Murakami, M.; Murray, B.J.; Niedermeier, D.; Petters, M.D.; O'Sullivan, D.; Saito, A.; Schill, G.P.; Tajiri, T.; Tolbert, M.A.; Welti, A.; Whale, T.F.; Wright, T.P.; Yamashita, K.Immersion freezing is the most relevant heterogeneous ice nucleation mechanism through which ice crystals are formed in mixed-phase clouds. In recent years, an increasing number of laboratory experiments utilizing a variety of instruments have examined immersion freezing activity of atmospherically relevant ice-nucleating particles. However, an intercomparison of these laboratory results is a difficult task because investigators have used different ice nucleation (IN) measurement methods to produce these results. A remaining challenge is to explore the sensitivity and accuracy of these techniques and to understand how the IN results are potentially influenced or biased by experimental parameters associated with these techniques. Within the framework of INUIT (Ice Nuclei Research Unit), we distributed an illite-rich sample (illite NX) as a representative surrogate for atmospheric mineral dust particles to investigators to perform immersion freezing experiments using different IN measurement methods and to obtain IN data as a function of particle concentration, temperature (T), cooling rate and nucleation time. A total of 17 measurement methods were involved in the data intercomparison. Experiments with seven instruments started with the test sample pre-suspended in water before cooling, while 10 other instruments employed water vapor condensation onto dry-dispersed particles followed by immersion freezing. The resulting comprehensive immersion freezing data set was evaluated using the ice nucleation active surface-site density, ns, to develop a representative ns(T) spectrum that spans a wide temperature range (−37 °C < T < −11 °C) and covers 9 orders of magnitude in ns. In general, the 17 immersion freezing measurement techniques deviate, within a range of about 8 °C in terms of temperature, by 3 orders of magnitude with respect to ns. In addition, we show evidence that the immersion freezing efficiency expressed in ns of illite NX particles is relatively independent of droplet size, particle mass in suspension, particle size and cooling rate during freezing. A strong temperature dependence and weak time and size dependence of the immersion freezing efficiency of illite-rich clay mineral particles enabled the ns parameterization solely as a function of temperature. We also characterized the ns(T) spectra and identified a section with a steep slope between −20 and −27 °C, where a large fraction of active sites of our test dust may trigger immersion freezing. This slope was followed by a region with a gentler slope at temperatures below −27 °C. While the agreement between different instruments was reasonable below ~ −27 °C, there seemed to be a different trend in the temperature-dependent ice nucleation activity from the suspension and dry-dispersed particle measurements for this mineral dust, in particular at higher temperatures. For instance, the ice nucleation activity expressed in ns was smaller for the average of the wet suspended samples and higher for the average of the dry-dispersed aerosol samples between about −27 and −18 °C. Only instruments making measurements with wet suspended samples were able to measure ice nucleation above −18 °C. A possible explanation for the deviation between −27 and −18 °C is discussed. Multiple exponential distribution fits in both linear and log space for both specific surface area-based ns(T) and geometric surface area-based ns(T) are provided. These new fits, constrained by using identical reference samples, will help to compare IN measurement methods that are not included in the present study and IN data from future IN instruments.