Browsing by Subject "BOUNDARY-LAYER"

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  • Oswald, R.; Ermel, M.; Hens, K.; Novelli, A.; Ouwersloot, H. G.; Paasonen, Pauli; Petäjä, Tuukka; Sipilä, Mikko; Keronen, Petri; Bäck, Jaana; Konigstedt, R.; Beygi, Z. Hosaynali; Fischer, H.; Bohn, B.; Kubistin, D.; Harder, H.; Martinez, M.; Williams, J.; Hoffmann, T.; Trebs, I.; Soergel, M. (2015)
  • Mazon, Stephany Buenrostro; Kontkanen, Jenni; Manninen, Hanna E.; Nieminen, Tuomo; Kerminen, Veli-Matti; Kulmala, Markku (2016)
    New particle formation (NPF) events are typically observed during daytime when photochemical oxidation takes place. However, nighttime nucleation mode particles have been observed across various locations only sporadically. We present 11 years (2003-2013) of air ion number size distribution data from the SMEAR II station in Hyytiala, Finland, where during a third of the nights a sub-3 nm negative (n = 1324 days) and positive (n = 1174 days) ion events took place. To investigate nocturnal clustering at sizes above the constant small ion pool, we defined cluster events (CE) as a nocturnal event with 2-3 nm ion concentrations reaching 70 cm-3 between 18:00 and 24:00 local time. CE (n = 221 days) were characterized by a rapid, 10-fold increase in the median 2-3 nm ion concentration from the start (similar to 10 cm(-3)) to the event peak (similar to 100 cm(-3)). Furthermore, small and intermediate ions during the CE, NPF events and nonevents were compared: while concentrations of 1.5-2 nm ions were the highest during CE (median 235 cm(-3)), as compared with the NPF events (96 cm(-3)) or the daytime and nighttime nonevents (similar to 20 cm(-3)), 3-7 nm ion concentrations increased notably only during NPF events (median 52 cm(-3)). Specifically, ion concentrations during CE decreased for sizes above-2.4 nm (<10 cm(-3)). In addition, 90% of CE proceeded either a NPF event (55%) or a undefined day (35%), and only 10% of them proceeded a daytime non-event. This study suggests a build-up of 0.9-2.4 nm ion clusters during CE nights (18:00-24:00) that equals or exceeds the ion concentration levels during daytime NPF, but unlike the latter, CE fail to activate and grow clusters > 3 nm in diameter in nighttime Hyytiald.
  • Vakkari, Ville; Manninen, Antti J.; O'Connor, Ewan; Schween, Jan H.; Van Zyl, Pieter G.; Marinou, Eleni (2019)
    Commercially available Doppler lidars have now been proven to be efficient tools for studying winds and turbulence in the planetary boundary layer. However, in many cases low signal-to-noise ratio is still a limiting factor for utilising measurements by these devices. Here, we present a novel post-processing algorithm for Halo Stream Line Doppler lidars, which enables an improvement in sensitivity of a factor of 5 or more. This algorithm is based on improving the accuracy of the instrumental noise floor and it enables longer integration times or averaging of high temporal resolution data to be used to obtain signals down to -32 dB. While this algorithm does not affect the measured radial velocity, it improves the accuracy of radial velocity uncertainty estimates and consequently the accuracy of retrieved turbulent properties. Field measurements using three different Halo Doppler lidars deployed in Finland, Greece and South Africa demonstrate how the new post-processing algorithm increases data availability for turbulent retrievals in the planetary boundary layer, improves detection of high-altitude cirrus clouds and enables the observation of elevated aerosol layers.
  • Paton, Mark; Harri, Ari-Matti; Vierkens, Oliver; Savijärvi, Hannu (2019)
    As spacecraft missions return ever more data from Mars, additional tools will be required to explore and analyse these datasets efficiently. To streamline research into the atmosphere of Mars, a user-orientated modelling capability is developed that enables automatic initialisation and running of a column model. As a demonstration we utilise the modelling framework to provide additional verification for the University of Helsinki and Finnish Meteorological Institute Mars column model temperature profiles above the height of typical lander meteorological measurements, i.e. above 2 m. We utilise the framework at landing site locations that are well characterised to understand the model's applicability and to identify future opportunities for modifications to the framework. We do this by using the framework to compare the column model to temperature soundings made by the Mars Reconnaissance Orbiter. We find that the column model, without any modification, is able to reproduce the observed lapse rates and average temperatures closely in most cases except for a 20-60 K increase over the northern hemisphere mid-winter. We can reproduce this discrepancy by incorporating an adiabatic heating term into the column model. Fitting of the modified column model to the observations results in estimated maximum downward vertical wind velocities of similar to 10 cm s(-1) at altitudes of 15-20 km over the winter solstice at the VL-1 and VL-2 sites. The approach developed here may possibly provide a way to independently estimate or observe the vertical motion in the Martian atmosphere. However, even though the magnitude of the vertical wind speed appears reasonable, it is not clear at this point how much the atmospheric heating is due to other mechanisms such as advection. We have introduced new application software that can quickly find and display the requested data and can be immediately analysed using the included tools. We have demonstrated the potential of this type of software application with a glimpse into the upper atmosphere of Mars.
  • Rannik, Ullar; Zhou, Luxi; Zhou, Putian; Gierens, Rosa; Mammarella, Ivan; Sogachev, Andrey; Boy, Michael (2016)
    A 1-D atmospheric boundary layer (ABL) model coupled with a detailed atmospheric chemistry and aerosol dynamical model, the model SOSAA, was used to predict the ABL and detailed aerosol population (characterized by the number size distribution) time evolution. The model was applied over a period of 10 days in May 2013 to a pine forest site in southern Finland. The period was characterized by frequent new particle formation events and simultaneous intensive aerosol transformation. The aim of the study was to analyze and quantify the role of aerosol and ABL dynamics in the vertical transport of aerosols. It was of particular interest to what extent the fluxes above the canopy deviate from the particle dry deposition on the canopy foliage due to the above-mentioned processes. The model simulations revealed that the particle concentration change due to aerosol dynamics frequently exceeded the effect of particle deposition by even an order of magnitude or more. The impact was, however, strongly dependent on particle size and time. In spite of the fact that the timescale of turbulent transfer inside the canopy is much smaller than the timescales of aerosol dynamics and dry deposition, leading us to assume well-mixed properties of air, the fluxes at the canopy top frequently deviated from deposition inside the forest. This was due to transformation of aerosol concentration throughout the ABL and resulting complicated pattern of vertical transport. Therefore we argue that the comparison of timescales of aerosol dynamics and deposition defined for the processes below the flux measurement level do not unambiguously describe the importance of aerosol dynamics for vertical transport above the canopy. We conclude that under dynamical conditions reported in the current study the micrometeorological particle flux measurements can significantly deviate from the dry deposition into the canopy. The deviation can be systematic for certain size ranges so that the time-averaged particle fluxes can be also biased with respect to deposition sink.
  • Shen, Yicheng; Virkkula, Aki; Ding, Aijun; Wang, Jiaping; Chi, Xuguang; Nie, Wei; Qi, Ximeng; Huang, Xin; Liu, Qiang; Zheng, Longfei; Xu, Zheng; Petäjä, Tuukka; Aalto, Pasi P.; Fu, Congbin; Kulmala, Markku (2018)
    Aerosol optical properties (AOPs) and supporting parameters-particle number size distributions, PM2 : 5 mass concentrations, and the concentrations of trace gases (NOx and NOy) - were measured at SORPES, a regional background station in Nanjing, China from June 2013 to May 2015. The aerosol was highly scattering: the average scattering coefficient was sigma(sp) =403 +/- 314Mm 1, the absorption coefficient sigma(ap) =26 +/- 19Mm 1, and the single-scattering albedo SS Lambda =0.93 +/- 0.03 for green light. The SSA in Nanjing appears to be slightly higher than published values from several other sites in China and elsewhere. The average Angstrom exponent of absorption (AAE) for the wavelength range 370-950 nm was 1.04 and the AAE range was 0.7-1.4. These AAE values can be explained with different amounts of non-absorbing coating on pure black carbon (BC) cores and different core sizes rather than contribution by brown carbon. The AOPs had typical seasonal cycles with high sigma(sp) and sigma(ap) in winter and low ones in summer: the averages were sigma(sp) =544 +/- 422 and sigma(ap) =36 +/- 24Mm 1 in winter and sigma(sp) =342 +/- 281 and sigma(ap) =20 +/- 13Mm 1 in summer. The intensive AOPs had no clear seasonal cycles, the variations in them were rather related to the evolution of pollution episodes. The diurnal cycles of the intensive AOPs were clear and in agreement with the cycle of the particle number size distribution. The diurnal cycle of SSA was similar to that of the air photochemical age, suggesting that the darkest aerosol originated from fresh traffic emissions. A Lagrangian retroplume analysis showed that the potential source areas of high sigma(sp) and sigma(ap) are mainly in eastern China. Synoptic weather phenomena dominated the cycle of AOPs on a temporal scale of 3-7 days. During pollution episodes, modeled boundary layer height decreased, whereas PM2.5 concentrations and sigma(sp) and sigma(ap) typically increased gradually and remained high during several days but decreased faster, sometimes by even more than an order of magnitude within some hours. During the growth phase of the pollution episodes the intensive AOPs evolved clearly. The mass scattering efficiency MSE of PM2.5 grew during the extended pollution episodes from similar to 4 to similar to 6m(2) g(-1) and the mass fraction of BCe decreased from similar to 10 to similar to 3% during the growth phase of the episodes. Particle growth resulted in the backscatter fraction decreasing from more than 0.16 to less than 0.10, SSA growing from less than 0.9 to more than 0.95, and radiative forcing efficiency (RFE) changing from less than -26Wm(-2) to more than 24Wm(-2), which means that the magnitude of RFE decreased. The RFE probability distribution at SORPES was clearly narrower than at a clean background site which is in agreement with a published RFE climatology.
  • Chu, Biwu; Kerminen, Veli-Matti; Bianchi, Federico; Yan, Chao; Petäjä, Tuukka; Kulmala, Markku (2019)
    New particle formation (NPF) studies in China were summarized comprehensively in this paper. NPF frequency, formation rate, and particle growth rate were closely compared among the observations carried out at different types of sites in different regions of China in different seasons, with the aim of exploring the nucleation and particle growth mechanisms. The interactions between air pollution and NPF are discussed, emphasizing the properties of NPF under heavy pollution conditions. The current understanding of NPF cannot fully explain the frequent occurrence of NPF at high aerosol loadings in China, and possible reasons for this phenomenon are proposed. The effects of NPF and some aspects of NPF research requiring further investigation are also summarized in this paper.
  • Gordon, Hamish; Kirkby, Jasper; Baltensperger, Urs; Bianchi, Federico; Breitenlechner, Martin; Curtius, Joachim; Dias, Antonio; Dommen, Josef; Donahue, Neil M.; Dunne, Eimear M.; Duplissy, Jonathan; Ehrhart, Sebastian; Flagan, Richard C.; Frege, Carla; Fuchs, Claudia; Hansel, Armin; Hoyle, Christopher R.; Kulmala, Markku; Kurten, Andreas; Lehtipalo, Katrianne; Makhmutov, Vladimir; Molteni, Ugo; Rissanen, Matti P.; Stozkhov, Yuri; Trostl, Jasmin; Tsagkogeorgas, Georgios; Wagner, Robert; Williamson, Christina; Wimmer, Daniela; Winkler, Paul M.; Yan, Chao; Carslaw, Ken S. (2017)
    New particle formation has been estimated to produce around half of cloud-forming particles in the present-day atmosphere, via gas-to-particle conversion. Here we assess the importance of new particle formation (NPF) for both the present-day and the preindustrial atmospheres. We use a global aerosol model with parametrizations of NPF from previously published CLOUD chamber experiments involving sulfuric acid, ammonia, organic molecules, and ions. We find that NPF produces around 67% of cloud condensation nuclei at 0.2% supersaturation (CCN0.2%) at the level of low clouds in the preindustrial atmosphere (estimated uncertainty range 45-84%) and 54% in the present day (estimated uncertainty range 38-66%). Concerning causes, we find that the importance of biogenic volatile organic compounds (BVOCs) in NPF and CCN formation is greater than previously thought. Removing BVOCs and hence all secondary organic aerosol from our model reduces low-cloud-level CCN concentrations at 0.2% supersaturation by 26% in the present-day atmosphere and 41% in the preindustrial. Around three quarters of this reduction is due to the tiny fraction of the oxidation products of BVOCs that have sufficiently low volatility to be involved in NPF and early growth. Furthermore, we estimate that 40% of preindustrial CCN0.2% are formed via ion-induced NPF, compared with 27% in the present day, although we caution that the ion-induced fraction of NPF involving BVOCs is poorly measured at present. Our model suggests that the effect of changes in cosmic ray intensity on CCN is small and unlikely to be comparable to the effect of large variations in natural primary aerosol emissions. Plain Language Summary New particle formation in the atmosphere is the process by which gas molecules collide and stick together to form atmospheric aerosol particles. Aerosols act as seeds for cloud droplets, so the concentration of aerosols in the atmosphere affects the properties of clouds. It is important to understand how aerosols affect clouds because they reflect a lot of incoming solar radiation away from Earth's surface, so changes in cloud properties can affect the climate. Before the Industrial Revolution, aerosol concentrations were significantly lower than they are today. In this article, we show using global model simulations that new particle formation was a more important mechanism for aerosol production than it is now. We also study the importance of gases emitted by vegetation, and of atmospheric ions made by radon gas or cosmic rays, in preindustrial aerosol formation. We find that the contribution of ions and vegetation to new particle formation was also greater in the preindustrial period than it is today. However, the effect on particle formation of variations in ion concentration due to changes in the intensity of cosmic rays reaching Earth was small.
  • Li, Dan; Katul, Gabriel G.; Zilitinkevich, Sergej S. (2016)
    Two recently proposed turbulence closure schemes are compared against the conventional Mellor-Yamada (MY) model for stably stratified atmospheric flows. The Energy and Flux-Budget (EFB) approach solves the budgets of turbulent momentum and heat fluxes and turbulent kinetic and potential energies. The Cospectral Budget (CSB) approach is formulated in wavenumber space and integrated across all turbulent scales to obtain flow variables in physical space. Unlike the MY model, which is subject to a "critical gradient Richardson number," both EFB and CSB models allow turbulence to exist at any gradient Richardson number R-t and predict a saturation of flux Richardson number (R-f -> R-fm) at sufficiently large R-i. The CSB approach further predicts the value of Rim and reveals a unique expression linking the Rotta and von Karman constants. Hence, all constants in the CSB model are nontunable and stability independent. All models agree that the dimensionless sensible heat flux decays with increasing R-i. However, the decay rate and subsequent cutoff in the MY model appear abrupt. The MY model further exhibits an abrupt cutoff in the turbulent stress normalized by vertical velocity variance, while the CSB and EFB models display increasing trends. The EFB model produces a rapid increase in the ratio of turbulent potential energy and vertical velocity variance as Rim is approached, suggesting a strong self-preservation mechanism. Vertical anisotropy in the turbulent kinetic energy is parameterized in different ways in MY and EFB, but this consideration is not required in CSB. Differences between EFB and CSB model predictions originate from how the vertical anisotropy is specified in the EFB model.
  • Nikandrova, Anna; Tabakova, Ksenia; Manninen, Antti J.; Väänänen, Riikka; Petäjä, Tuukka; Kulmala, Markku; Kerminen, Veli-Matti; O'Connor, Ewan (2018)
    Understanding the distribution of aerosol layers is important for determining long-range transport and aerosol radiative forcing. In this study we combine airborne in situ measurements of aerosol with data obtained by a ground-based high spectral resolution lidar (HSRL) and radiosonde profiles to investigate the temporal and vertical variability of aerosol properties in the lower troposphere. The HSRL was deployed in Hyytiala, southern Finland, from January to September 2014 as a part of the U.S. DOE ARM (Atmospheric Radiation Measurement) mobile facility during the BAECC (Biogenic Aerosols - Effects on Cloud and Climate) Campaign. Two flight campaigns took place in April and August 2014 with instruments measuring the aerosol size distribution from 10 nm to 5 mu m at altitudes up to 3800 m. Two case studies with several aerosol layers present were selected from the flight campaigns for further investigation: one clear-sky and one partly cloudy case. During the clear-sky case, turbulent mixing ensured small temporal and spatial variability in the measured aerosol size distribution in the boundary layer, whereas mixing was not as homogeneous in the boundary layer during the partly cloudy case. The elevated layers exhibited larger temporal and spatial variability in aerosol size distribution, indicating a lack of mixing. New particle formation was observed in the boundary layer during the clear-sky case, and nucleation mode particles were also seen in the elevated layers that were not mixing with the boundary layer. Interpreting local measurements of elevated layers in terms of long-range transport can be achieved using back trajectories from Lagrangian models, but care should be taken in selecting appropriate arrival heights, since the modelled and observed layer heights did not always coincide. We conclude that higher confidence in attributing elevated aerosol layers to their air mass origin is attained when back trajectories are combined with lidar and radiosonde profiles.
  • Huang, Xin; Zhou, Luxi; Ding, Aijun; Qi, Ximeng; Nie, Wei; Wang, Minghuai; Chi, Xuguang; Petäjä, Tuukka; Kerminen, Veli-Matti; Roldin, Pontus; Rusanen, Anton; Kulmala, Markku; Boy, Michael (2016)
    New particle formation (NPF) has been investigated intensively during the last 2 decades because of its influence on aerosol population and the possible contribution to cloud condensation nuclei. However, intensive measurements and modelling activities on this topic in urban metropolitan areas in China with frequent high-pollution episodes are still very limited. This study provides results from a comprehensive modelling study on the occurrence of NPF events in the western part of the Yangtze River Delta (YRD) region, China. The comprehensive modelling system, which combines the WRF-Chem (the Weather Research and Forecasting model coupled with Chemistry) regional chemical transport model and the MALTE-BOX sectional box model (the model to predict new aerosol formation in the lower troposphere), was shown to be capable of simulating atmospheric nucleation and subsequent growth. Here we present a detailed discussion of three typical NPF days, during which the measured air masses were notably influenced by either anthropogenic activities, biogenic emissions, or mixed ocean and continental sources. Overall, simulated NPF events were generally in good agreement with the corresponding measurements, enabling us to get further insights into NPF processes in the YRD region. Based on the simulations, we conclude that biogenic organic compounds, particularly monoterpenes, play an essential role in the initial condensational growth of newly formed clusters through their low-volatility oxidation products. Although some uncertain-ties remain in this modelling system, this method provides a possibility to better understand particle formation and growth processes.
  • Zhou, L.; Gierens, R.; Sogachev, A.; Mogensen, D.; Ortega, J.; Smith, J. N.; Harley, P. C.; Prenni, A. J.; Levin, E. J. T.; Turnipseed, A.; Rusanen, A.; Smolander, S.; Guenther, A. B.; Kulmala, Markku; Karl, T.; Boy, M. (2015)
    New particle formation (NPF) is an important atmospheric phenomenon. During an NPF event, particles first form by nucleation and then grow further in size. The growth step is crucial because it controls the number of particles that can become cloud condensation nuclei. Among various physical and chemical processes contributing to particle growth, condensation by organic vapors has been suggested as important. In order to better understand the influence of biogenic emissions on particle growth, we carried out modeling studies of NPF events during the BEACHON-ROCS (Biohydro-atmosphere interactions of Energy, Aerosol, Carbon, H2O, Organics & Nitrogen - Rocky Mountain Organic Carbon Study) campaign at Manitou Experimental Forest Observatory in Colorado, USA. The site is representative of the semi-arid western USA. With the latest Criegee intermediate reaction rates implemented in the chemistry scheme, the model underestimates sulfuric acid concentration by 50 %, suggesting either missing sources of atmospheric sulfuric acid or an overestimated sink term. The results emphasize the contribution from biogenic volatile organic compound emissions to particle growth by demonstrating the effects of the oxidation products of monoterpenes and 2-Methyl-3-buten-2-ol (MBO). Monoterpene oxidation products are shown to influence the nighttime particle loadings significantly, while their concentrations are insufficient to grow the particles during the day. The growth of ultrafine particles in the daytime appears to be closely related to the OH oxidation products of MBO.
  • Afonso, Marco Martins; Muratore-Ginanneschi, Paolo; Gama, Silvio M. A.; Mazzino, Andrea (2018)
    We investigate the large-scale transport properties of quasi-neutrally-buoyant inertial particles carried by incompressible zero-mean periodic or steady ergodic flows. We show howto compute large-scale indicators such as the inertial-particle terminal velocity and eddy diffusivity from first principles in a perturbative expansion around the limit of added-mass factor close to unity. Physically, this limit corresponds to the case where the mass density of the particles is constant and close in value to the mass density of the fluid, which is also constant. Our approach differs from the usual over-damped expansion inasmuch as we do not assume a separation of time scales between thermalization and small-scale convection effects. For a general flow in the class of incompressible zero-mean periodic velocity fields, we derive closed-form cell equations for the auxiliary quantities determining the terminal velocity and effective diffusivity. In the special case of parallel flows these equations admit explicit analytic solution. We use parallel flows to show that our approach sheds light onto the behavior of terminal velocity and effective diffusivity for Stokes numbers of the order of unity.
  • Rondo, L.; Ehrhart, S.; Kuerten, A.; Adamov, A.; Bianchi, F.; Breitenlechner, M.; Duplissy, J.; Franchin, A.; Dommen, J.; Donahue, N. M.; Dunne, E. M.; Flagan, R. C.; Hakala, J.; Hansel, A.; Keskinen, H.; Kim, J.; Jokinen, T.; Lehtipalo, K.; Leiminger, M.; Praplan, A.; Riccobono, F.; Rissanen, M. P.; Sarnela, N.; Schobesberger, S.; Simon, M.; Sipilä, M.; Smith, J. N.; Tome, A.; Trostl, J.; Tsagkogeorgas, G.; Vaattovaara, P.; Winkler, P. M.; Williamson, C.; Wimmer, D.; Baltensperger, U.; Kirkby, J.; Kulmala, M.; Petäjä, T.; Worsnop, D. R.; Curtius, J. (2016)
    Sulfuric acid is widely recognized as a very important substance driving atmospheric aerosol nucleation. Based on quantum chemical calculations it has been suggested that the quantitative detection of gas phase sulfuric acid (H2SO4) by use of Chemical Ionization Mass Spectrometry (CIMS) could be biased in the presence of gas phase amines such as dimethylamine (DMA). An experiment (CLOUD7 campaign) was set up at the CLOUD (Cosmics Leaving OUtdoor Droplets) chamber to investigate the quantitative detection of H2SO4 in the presence of dimethylamine by CIMS at atmospherically relevant concentrations. For the first time in the CLOUD experiment, the monomer sulfuric acid concentration was measured by a CIMS and by two CI-APi-TOF (Chemical Ionization-Atmospheric Pressure interface-Time Of Flight) mass spectrometers. In addition, neutral sulfuric acid clusters were measured with the CI-APi-TOFs. The CLOUD7 measurements show that in the presence of dimethylamine (
  • Kuerten, Andreas; Bianchi, Federico; Almeida, Joao; Kupiainen-Määttä, Oona; Dunne, Eimear M.; Duplissy, Jonathan; Williamson, Christina; Barmet, Peter; Breitenlechner, Martin; Dommen, Josef; Donahue, Neil M.; Flagan, Richard C.; Franchin, Alessandro; Gordon, Hamish; Hakala, Jani; Hansel, Armin; Heinritzi, Martin; Ickes, Luisa; Jokinen, Tuija; Kangasluoma, Juha; Kim, Jaeseok; Kirkby, Jasper; Kupc, Agnieszka; Lehtipalo, Katrianne; Leiminger, Markus; Makhmutov, Vladimir; Onnela, Antti; Ortega, Ismael K.; Petäjä, Tuukka; Praplan, Arnaud P.; Riccobono, Francesco; Rissanen, Matti P.; Rondo, Linda; Schnitzhofer, Ralf; Schobesberger, Siegfried; Smith, James N.; Steiner, Gerhard; Stozhkov, Yuri; Tome, Antonio; Trostl, Jasmin; Tsagkogeorgas, Georgios; Wagner, Paul E.; Wimmer, Daniela; Ye, Penglin; Baltensperger, Urs; Carslaw, Ken; Kulmala, Markku; Curtius, Joachim (2016)
    Binary nucleation of sulfuric acid and water as well as ternary nucleation involving ammonia are thought to be the dominant processes responsible for new particle formation (NPF) in the cold temperatures of the middle and upper troposphere. Ions are also thought to be important for particle nucleation in these regions. However, global models presently lack experimentally measured NPF rates under controlled laboratory conditions and so at present must rely on theoretical or empirical parameterizations. Here with data obtained in the European Organization for Nuclear Research CLOUD (Cosmics Leaving OUtdoor Droplets) chamber, we present the first experimental survey of NPF rates spanning free tropospheric conditions. The conditions during nucleation cover a temperature range from 208 to 298K, sulfuric acid concentrations between 5x10(5) and 1x10(9)cm(-3), and ammonia mixing ratios from zero added ammonia, i.e., nominally pure binary, to a maximum of -1400 parts per trillion by volume (pptv). We performed nucleation studies under pure neutral conditions with zero ions being present in the chamber and at ionization rates of up to 75ion pairs cm(-3)s(-1) to study neutral and ion-induced nucleation. We found that the contribution from ion-induced nucleation is small at temperatures between 208 and 248K when ammonia is present at several pptv or higher. However, the presence of charges significantly enhances the nucleation rates, especially at 248K with zero added ammonia, and for higher temperatures independent of NH3 levels. We compare these experimental data with calculated cluster formation rates from the Atmospheric Cluster Dynamics Code with cluster evaporation rates obtained from quantum chemistry.
  • Arriga, Nicola; Rannik, Ullar; Aubinet, Marc; Carrara, Arnaud; Vesala, Timo; Papale, Dario (2017)
    Footprint models, which simulate source area for scalar fluxes, are fundamental tools for a correct interpretation of micromoeteorological flux measurements and ecosystem exchange inferred from such data. Over the last two decades models of varying complexity have been developed, but all of them suffer from a significant lack of experimental validation. In this study two different experimental tests have been conducted with the aim of offering validation: a manipulation of the vegetation cover and an artificial tracer emission. In the first case the extension of the flux source has been changed progressively by successive cuts of vegetation, while in the second case by varying the distance of a tracer emission line respect to the measurement point. Results have been used to validate two analytical and a numerical footprint models. The experimental data show a good agreement with footprint models and indicate a limited extension of the flux source area, with approximately 75% of the sources confined within a range of 10-20 times the effective measurement height, i.e. the measurement height above the zero plane displacement. Another interesting result was the strong dependence on the surface roughness of both experimental estimates and numerical simulations of footprint. The effect of surface roughness on experimental results and models outputs was comparable to the effect of atmospheric stability. This indicates that surface roughness and turbulence conditions may play a significant role in source area location, in particular above inhomogeneous surfaces with change in roughness, as in the case of the manipulation experiment. Consequently a careful site specific quantification of these parameters seems to be fundamental to obtain realistic footprint estimates and significantly improve eddy covariance flux interpretation at complex sites.
  • Li, Mingge; Wang, Lili; Liu, Jingda; Gao, Wenkang; Song, Tao; Sun, Yang; Li, Liang; Li, Xingru; Wang, Yonghong; Liu, Lili; Dällenbach, Kaspar; Paasonen, Pauli J.; Kerminen, Veli-Matti; Kulmala, Markku; Wang, Yuesi (2020)
    In the last decade, North China (NC) has been one of the most populated and polluted regions in the world. The regional air pollution has had a serious impact on people's health; thus, all levels of government have implemented various pollution prevention measures since 2013. Based on multi-city in situ environmental and meteorological data, as well as the meteorological reanalysis dataset from 2013 to 2017, regional pollution characteristics and meteorological formation mechanisms were analyzed to provide a more comprehensive understanding of the evolution of PM2.5 in NC. The domain-averaged PM2.5 was 79 +/- 17 mu g m(-3) from 2013 to 2017, with a decreasing rate of 10 mu g m(-3) yr(-1). Two automatic computer algorithms were established to identify 6 daily regional pollution types (DRPTs) and 48 persistent regional pollution events (PRPEs) over NC during 2014-2017. The average PM2.5 concentration for the Large-Region-Pollution type (including the Large-Moderate-Region-Pollution and Large-Severe-Region-Pollution types) was 113 +/- 40 mu g m(-3), and more than half of Large-Region-Pollution days and PRPEs occurred in winter. The PRPEs in NC mainly developed from the area south of Hebei. The number of Large-Region-Pollution days decreased notably from 2014 to 2017, the annual number of days varying between 194 and 97 days, whereas a slight decline was observed in winter. In addition, the averaged PM2.5 concentrations and the numbers and durations of the PRPEs decreased. Lamb-Jenkinson weather typing was used to reveal the impact of synoptic circulations on PM2.5 across NC. Generally, the contributions of the variations in circulation to the reduction in PM2.5 levels over NC between 2013 and 2017 were 64% and 45% in summer and winter, respectively. The three most highly polluted weather types were types C, S and E, with an average PM2.5 concentration of 137 +/- 40 mu g m(-3) in winter. Furthermore, three typical circulation dynamics were categorized in the peak stage of the PRPEs, namely, the southerly airflow pattern, the northerly airflow pattern and anticyclone pattern; the averaged relative humidity, recirculation index, wind speed and boundary layer height were 63%, 0.33, 2.0 m s(-1) and 493 m, respectively. Our results imply that additional emission reduction measures should be implemented under unfavorable meteorological situations to attain ambient air quality standards in the future.
  • Yan, Chao; Tham, Yee Jun; Zha, Qiaozhi; Wang, Xinfeng; Xue, Likun; Dai, Jianing; Wang, Zhe; Wang, Tao (2019)
    Nitrate radical (NO3) and dinitrogen pentoxide (N2O5) play crucial roles in the nocturnal atmosphere. To quantify their impacts, we deployed a thermal-dissociation chemical ionization mass spectrometry (TD-CIMS), to measure their concentration, as well as ClNO2 at a coastal background site in the southern of China during the late autumn of 2012. Moderate levels of NO3, N2O5 and high concentration of ClNO2 were observed during the study period, indicating active NOx-O-3 chemistry in the region. Distinct features of NO3, N2O5 and ClNO2 mixing ratios were observed in different airmasses. Further analysis revealed that the N2O5 heterogeneous reaction was the dominant loss of N2O5 and NO3, which showed higher loss rate compared to that in other coastal sites. Especially, the N2O5 loss rates could reach up to 0.0139 s(-1) when airmasses went across the sea. The fast heterogeneous loss of N2O5 led to rapid NOx loss which could be comparable to the daytime process through NO2 oxidization by OH, and on the other hand, to rapid nitrate aerosol formation. In summary, our results revealed that the N2O5 hydrolysis could play significant roles in regulating the air quality by reducing NOx but forming nitrate aerosols. (C) 2019 Published by Elsevier B.V.
  • Lee, Ben H.; Lopez-Hilfiker, Felipe D.; Veres, Patrick R.; McDuffie, Erin E.; Fibiger, Dorothy L.; Sparks, Tamara L.; Ebben, Carlena J.; Green, Jaime R.; Schroder, Jason C.; Campuzano-Jost, Pedro; Iyer, Siddharth; D'Ambro, Emma L.; Schobesberger, Siegfried; Brown, Steven S.; Wooldridge, Paul J.; Cohen, Ronald C.; Fiddler, Marc N.; Bililign, Solomon; Jimenez, Jose L.; Kurten, Theo; Weinheimer, Andrew J.; Jaegle, Lyatt; Thornton, Joel A. (2018)
    We describe the University of Washington airborne high-resolution time-of-flight chemical ionization mass spectrometer (HRToF-CIMS) and evaluate its performance aboard the NCAR-NSF C-130 aircraft during the recent Wintertime INvestigation of Transport, Emissions and Reactivity (WINTER) experiment in February-March of 2015. New features include (i) a computer-controlled dynamic pinhole that maintains constant mass flow-rate into the instrument independent of altitude changes to minimize variations in instrument response times; (ii) continuous addition of low flow-rate humidified ultrahigh purity nitrogen to minimize the difference in water vapor pressure, hence instrument sensitivity, between ambient and background determinations; (iii) deployment of a calibration source continuously generating isotopically labeled dinitrogen pentoxide ((N2O5)-N-15) for in-flight delivery; and (iv) frequent instrument background determinations to account for memory effects resulting from the interaction between sticky compounds and instrument surface following encounters with concentrated air parcels. The resulting improvements to precision and accuracy, along with the simultaneous acquisition of these species and the full set of their isotopologues, allow for more reliable identification, source attribution, and budget accounting, for example, by speciating the individual constituents of nocturnal reactive nitrogen oxides (NOz=ClNO2+2xN(2)O(5)+HNO3+etc.). We report on an expanded set of species quantified using iodide-adduct ionization such as sulfur dioxide (SO2), hydrogen chloride (HCl), and other inorganic reactive halogen species including hypochlorous acid, nitryl chloride, chlorine, nitryl bromide, bromine, and bromine chloride (HOCl, ClNO2, Cl-2, BrNO2, Br-2, and BrCl, respectively).
  • Wimmer, Daniela; Mazon, Stephany Buenrostro; Manninen, Hanna Elina; Kangasluoma, Juha; Franchin, Alessandro; Nieminen, Tuomo; Backman, John; Wang, Jian; Kuang, Chongai; Krejci, Radovan; Brito, Joel; Morais, Fernando Goncalves; Martin, Scot Turnbull; Artaxo, Paulo; Kulmala, Markku; Kerminen, Veli-Matti; Petäjä, Tuukka (2018)
    We investigated atmospheric new particle formation (NPF) in the Amazon rainforest using direct measurement methods. To our knowledge this is the first direct observation of NPF events in the Amazon region. However, previous observations elsewhere in Brazil showed the occurrence of nucleation-mode particles. Our measurements covered two field sites and both the wet and dry season. We measured the variability of air ion concentrations (0.8-12 nm) with an ion spectrometer between September 2011 and January 2014 at a rainforest site (T0t). Between February and October 2014, the same measurements were performed at a grassland pasture site (T3) as part of the GoAmazon 2014/5 experiment, with two intensive operating periods (IOP1 and IOP2 during the wet and the dry season, respectively). The GoAmazon 2014/5 experiment was designed to study the influence of anthropogenic emissions on the changing climate in the Amazon region. The experiment included basic aerosol and trace gas measurements at the ground, remote sensing instrumentation, and two aircraft-based measurements. The results presented in this work are from measurements performed at ground level at both sites. The site inside the rainforest (T0t) is located 60 km NNW of Manaus and influenced by pollution about once per week. The pasture (T3) site is located 70 km downwind from Manaus and influenced by the Manaus pollution plume typically once per day or every second day, especially in the afternoon. No NPF events were observed inside the rainforest (site T0t) at ground level during the measurement period. However, rain-induced ion and particle bursts (hereafter, "rain events") occurred frequently (643 of 1031 days) at both sites during the wet and dry season, being most frequent during the wet season. During the rain events, the ion concentrations in three size ranges (0.8-2, 2-4, and 4-12 nm) increased up to about 10(4)-10(5) cm(-3). This effect was most pronounced in the intermediate and large size ranges, for which the background ion concentrations were about 10-15 cm(-3) compared with 700 cm(-3) for the cluster ion background. We observed eight NPF events at the pasture site during the wet season. We calculated the growth rates and formation rates of neutral particles and ions for the size ranges 2-3 and 3-7 nm using the ion spectrometer data. The observed median growth rates were 0.8 and 1.6 nm h(-1) for 2-3 nm sized ions and particles, respectively, with larger growth rates (13.3 and 7.9 nm h(-1)) in the 3-7 nm size range. The measured nucleation rates were of the order of 0.2 cm(-3) s(-1) for particles and 4-9 x 10(-3) cm(-3) s(-1) for ions. There was no clear difference in the sulfuric acid concentrations between the NPF event days and nonevent days (similar to 9 x 10(5) cm(-3)). The two major differences between the NPF days and nonevent days were a factor of 1.8 lower condensation sink on NPF event days (1.8 x 10(-3) s(-1)) compared to nonevents (3.2 x 10(-3) s(-1)) and different air mass origins. To our knowledge, this is the first time that results from ground-based sub-3 nm aerosol particle measurements have been obtained from the Amazon rainforest.