82 research outputs found
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An overview of the ACE-2 clear sky column closure experiment (CLEARCOLUMN)
As 1 of 6 focused ACE-2 activities, a clear sky column closure experiment (CLEARCOLUMN)
took place in June/July 1997 at the southwest corner of Portugal, in the Canary Islands, and
over the eastern Atlantic Ocean surrounding and linking those sites. Overdetermined sets of
volumetric, vertical profile and columnar aerosol data were taken from the sea surface to~5 km
asl by samplers and sensors at land sites (20–3570 m asl), on a ship, and on 4 aircraft. In
addition, 5 satellites measured upwelling radiances used to derive properties of the aerosol
column. Measurements were made in a wide range of conditions and locations (e.g., the marine
boundary layer with and without continental pollution, the free troposphere with and without
African dust). Numerous tests of local and column closure, using unidisciplinary and multidisciplinary
approaches, were conducted. This paper summarizes the methodological approach, the
experiment sites and platforms, the types of measurements made on each, the types of analyses
conducted, and selected key results, as a guide to the more complete results presented in other
papers in this special issue and elsewhere. Example results include determinations of aerosol
single scattering albedo by several techniques, measurements of hygroscopic effects on particle
light scattering and size, and a wide range in the degree of agreement found in closure tests. In
general, the smallest discrepancies were found in comparisons among (1) different techniques
to measure an optical property of the ambient, unperturbed aerosol (e.g., optical depth, extinction,
or backscatter by sunphotometer, lidar, and/or satellite) or (2) different techniques to
measure an aerosol that had passed through a common sampling process (e.g., nephelometer
and size spectrometer measurements with the same or similar inlets, humidities and temperatures).
Typically, larger discrepancies were found between techniques that measure the ambient,
unperturbed aerosol and those that must reconstruct the ambient aerosol by accounting for
(a) processes that occur during sampling (e.g., aerodynamic selection, evaporation of water and
other volatile material) or ( b) calibrations that depend on aerosol characteristics (e.g., sizedependent
density or refractive index). A primary reason for the discrepancies in such cases is
the lack of validated hygroscopic growth models covering the necessary range of particle sizes
and compositions. Other common reasons include (1) using analysis or retrieval techniques
that assume aerosol properties (e.g., density, single scattering albedo, shape) that do not apply
in all cases and (2) using surface measurements to estimate column properties. Taken together,
the ACE-2 CLEARCOLUMN data set provides a large collection of new information on the
properties of the aerosol over the northeast Atlantic Ocean. CLEARCOLUMN studies have
also pointed to improved techniques for analyzing current and future data sets (including
satellite data sets) which will provide a more accurate and comprehensive description of the
Atlantic–European–African aerosol. Thus they set the stage for an improved regional quantification
of radiative forcing by anthropogenic aerosols
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The atmospheric aerosol over Siberia, as seen from the 300 m ZOTTO tower
This report describes a unique setup for aerosol measurements at the new long-term Tall Tower monitoring facility near Zotino, Siberia (ZOTTO). Through two inlets at 50 and 300 m aerosol particle number size distributions are measured since September 2006 in the size range 15–835 nanometer dry diameter. Until the end of May 2007 total number (N300) concentrations at 300 m height ranged between 400 cm-3 (5%) and 4000 cm-3 (95%) with a median of 1200 cm-3, which is rather high for a nearly uninhabited boreal forest region during the low productivity period of the year.
Fitting 1-h average distributions with a maximum of four lognormal functions yielded frequent ultrafine modes below 20 nm at 50 m height than at 300 m, whereas the latter height more frequently showed an aged nucleation mode near 30 nm. The positions of Aitken (≈80 nm) and accumulation modes (≈210 nm) were very similar at both inlet heights, the very sharp latter one being the most frequent of all modes. The encouraging first results let us expect exciting newfindings during the summer period with frequent forest fires and secondary particle sources from vegetation emissions
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Marine nanogels as a source of atmospheric nanoparticles in the high Arctic
The high Arctic (north of 80°N) in summer is a region characterized by clean air and low abundances of preexisting particles. Marine colloidal nanogels i.e., assembled dissolved organic carbohydrate polymer networks have recently been confirmed to be present in both airborne particles and cloud water over the Arctic pack ice area. A novel route to atmospheric nanoparticles that appears to be operative in the high Arctic is suggested. It involves the injection of marine granular nanogels into the air from evaporating fog and cloud droplets, and is supported by observational and theoretical evidence obtained from a case study. Statistical analysis of the aerosol size distribution data recorded in the years 1991, 1996, 2001, and 2008 classified 75 nanoparticle events - covering 17% of the observed time period - as nanogel-type events, characterized by the spontaneous appearance of several distinct size bands below 200 nm diameter
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Aerosol pollution maps and trends over Germany with hourly data at four rural background stations from 2009 to 2018
A total of 10 years of hourly aerosol and gas data at four rural German stations have been combined with hourly back trajectories to the stations and inventories of the European Emissions Database for Global Atmospheric Research (EDGAR), yielding pollution maps over Germany of PM10, particle number concentrations, and equivalent black carbon (eBC). The maps reflect aerosol emissions modified with atmospheric processes during transport between sources and receptor sites. Compared to emission maps, strong western European emission centers do not dominate the downwind concentrations because their emissions are reduced by atmospheric processes on the way to the receptor area. PM10, eBC, and to some extent also particle number concentrations are rather controlled by emissions from southeastern Europe from which pollution transport often occurs under drier conditions. Newly formed particles are found in air masses from a broad sector reaching from southern Germany to western Europe, which we explain with gaseous particle precursors coming with little wet scavenging from this region.
Annual emissions for 2009 of PM10, BC, SO2, and NOx were accumulated along each trajectory and compared with the corresponding measured time series. The agreement of each pair of time series was optimized by varying monthly factors and annual factors on the 2009 emissions. This approach yielded broader summer emission minima than published values that were partly displaced from the midsummer positions. The validity of connecting the ambient concentration and emission of particulate pollution was tested by calculating temporal changes in eBC for subsets of back trajectories passing over two separate prominent emission regions, region A to the northwest and B to the southeast of the measuring stations. Consistent with reported emission data the calculated emission decreases over region A are significantly stronger than over region B
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Occurrence of an ultrafine particle mode less than 20 nm in diameter in the marine boundary layer during Arctic summer and autumn
The International Arctic Ocean Expedition 1991 (IAOE-91) provided a platform to study the occurrence and size distributions of ultrafine particles in the marine boundary layer (MBL) during Arctic summer and autumn. Measurements of both aerosol physics, and gas/particulate chemistry were taken aboard the Swedish icebreaker Oden. Three separate submicron aerosol modes were found: an ultrafine mode (Dp 100 nm). We evaluated correlations between ultrafine particle number concentrations and mean diameter with the entire measured physical, chemical, and meteorological data set. Multivariate statistical methods were then used to make these comparisons. A principal component (PC) analysis indicated that the observed variation in the data could be explained by the influence from several types of air masses. These were characterised by contributions from the open sea or sources from the surrounding continents and islands. A partial least square (PLS) regression of the ultrafine particle concentration was also used. These results implied that the ultrafine particles were produced above or in upper layers of the MBL and mixed downwards. There were also indications that the open sea acted as a source of the precursors for ultrafine particle production. No anti-correlation was found between the ultrafine and accumulation particle number concentrations, thus indicating that the sources were in separate air masses
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New insights in sources of the sub-micrometre aerosol at Mt. Zeppelin observatory (Spitsbergen) in the year 2015
In order to evaluate the potential impact of the Arctic anthropogenic emission sources it is essential to understand better the natural aerosol sources of the inner Arctic and the atmospheric processing of the aerosols during their transport in the Arctic atmosphere. A 1-year time series of chemically specific measurements of the sub-micrometre aerosol during 2015 has been taken at the Mt. Zeppelin observatory in the European Arctic. A source apportionment study combined measured molecular tracers as source markers, positive matrix factorization, analysis of the potential source distribution and auxiliary information from satellite data and ground-based observations. The annual average sub-micrometre mass was apportioned to regional background secondary sulphate (56%), sea spray (17%), biomass burning (15%), secondary nitrate (5.8%), secondary marine biogenic (4.5%), mixed combustion (1.6%), and two types of marine gel sources (together 0.7%). Secondary nitrate aerosol mainly contributed towards the end of summer and during autumn. During spring and summer, the secondary marine biogenic factor reached a contribution of up to 50% in some samples. The most likely origin of the mixed combustion source is due to oil and gas extraction activities in Eastern Siberia. The two marine polymer gel sources predominantly occurred in autumn and winter. The small contribution of the marine gel sources at Mt. Zeppelin observatory in summer as opposed to regions closer to the North Pole is attributed to differences in ocean biology, vertical distribution of phytoplankton, and the earlier start of the summer season
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Saharan Mineral Dust Experiments SAMUM-1 and SAMUM-2: What have we learned?
Two comprehensive field campaigns were conducted in 2006 and 2008 in the framework of the Saharan Mineral Dust Experiment (SAMUM) project. The relationship between chemical composition, shape morphology, size distribution and optical effects of the dust particles was investigated. The impact of Saharan dust on radiative transfer and the feedback of radiative effects upon dust emission and aerosol transport were studied. Field observations (ground-based, airborne and remote sensing) and modelling results were compared within a variety of dust closure experiments with a strong focus on vertical profiling. For the first time, multiwavelength Raman/polarization lidars and an airborne high spectral resolution lidar were involved in major dust field campaigns and provided profiles of the volume extinction coefficient of the particles at ambient conditions (for the full dust size distribution), of particle-shape-sensitive optical properties at several wavelengths, and a clear separation of dust and smoke profiles allowing for an estimation of the single-scattering albedo of the biomass-burning aerosol. SAMUM–1 took place in southern Morocco close to the Saharan desert in the summer of 2006, whereas SAMUM–2 was conducted in Cape Verde in the outflow region of desert dust and biomass-burning smoke from western Africa in the winter of 2008. This paper gives an overview of the SAMUM concept, strategy and goals, provides snapshots (highlights) of SAMUM–2 observations and modelling efforts, summarizes main findings of SAMUM–1 and SAMUM–2 and finally presents a list of remaining problems and unsolved questions
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Arctic haze over Central Europe
An extraordinary aerosol situation over Leipzig, Germany in April 2002 was investigated with a comprehensive
set of ground-based volumetric and columnar aerosol data, combined with aerosol profiles
from lidar, meteorological data from radiosondes and air mass trajectory calculations. Air masses
were identified to stem from the Arctic, partly influenced by the greater Moscow region. An evaluation
of ground-based measurements of aerosol size distributions during these periods showed that
the number concentrations below about 70 nm in diameter were below respective long-term average
data, while number, surface and volume concentrations of the particles larger than about 70 nm in
diameter were higher than the long-term averages. The lidar aerosol profiles showed that the imported
aerosol particles were present up to about 3 km altitude. The particle optical depth was up to 0.45 at
550 nm wavelength. With a one-dimensional spectral radiative transfer model top of the atmosphere
(TOA) radiative forcing of the aerosol layer was estimated for a period with detailed vertical information.
Solar aerosol radiative forcing values between −23 and −38 W m−2 were calculated, which are
comparable to values that have been reported in heavily polluted continental plumes outside the respective
source regions. The present report adds weight to previous findings of aerosol import to Europe,
pointing to the need for attributing the three-dimensional aerosol burden to natural and anthropogenic
sources as well as to aerosol imports from adjacent or distant source regions. In the present case, the
transport situation is further complicated by forward trajectories, indicating that some of the observed
Arctic haze may have originated in Central Europe. This aerosolwas transported to the European Arctic
before being re-imported in the modified and augmented form to its initial source region
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An optical particle size spectrometer for aircraft-borne measurements in IAGOS-CARIBIC
The particle number size distribution is an important parameter to characterize the atmospheric aerosol and its influence on the Earth's climate. Here we describe a new optical particle size spectrometer (OPSS) for measurements of the accumulation mode particle number size distribution in the tropopause region on board a passenger aircraft (IAGOS-CARIBIC observatory: In-service Aircraft for a Global Observing System – Civil Aircraft for Regular Investigation of the Atmosphere Based on an Instrument Container). A modified KS93 particle sensor from RION Co., Ltd., together with a new airflow system and a dedicated data acquisition system, is the key component of the CARIBIC OPSS. The instrument records individual particle pulse signal curves in the particle size range 130–1110 nm diameter (for a particle refractive index of 1.47-i0.006) together with a time stamp and thus allows the post-flight choice of the time resolution and the size distribution bin width. The CARIBIC OPSS has a 50 % particle detection diameter of 152 nm and a maximum asymptotic counting efficiency of 98 %. The instrument's measurement performance shows no pressure dependency and no particle coincidence for free tropospheric conditions. The size response function of the CARIBIC OPSS was obtained by a polystyrene latex calibration in combination with model calculations. Particle number size distributions measured with the new OPSS in the lowermost stratosphere agreed within a factor of 2 in concentration with balloon-borne measurements over western North America. Since June 2010 the CARIBIC OPSS is deployed once per month in the IAGOS-CARIBIC observatory
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