1,721,139 research outputs found
A global analysis of climate-relevant aerosol properties retrieved from the network of Global Atmosphere Watch (GAW) near-surface observatories
Get PDFAerosol particles are essential constituents of the Earth's atmosphere, impacting the earth radiation balance directly by scattering and absorbing solar radiation, and indirectly by acting as cloud condensation nuclei. In contrast to most greenhouse gases, aerosol particles have short atmospheric residence times, resulting in a highly heterogeneous distribution in space and time. There is a clear need to document this variability at regional scale through observations involving, in particular, the in situ near-surface segment of the atmospheric observation system. This paper will provide the widest effort so far to document variability of climate-relevant in situ aerosol properties (namely wavelength dependent particle light scattering and absorption coefficients, particle number concentration and particle number size distribution) from all sites connected to the Global Atmosphere Watch network. High-quality data from almost 90 stations worldwide have been collected and controlled for quality and are reported for a reference year in 2017, providing a very extended and robust view of the variability of these variables worldwide. The range of variability observed worldwide for light scattering and absorption coefficients, single-scattering albedo, and particle number concentration are presented together with preliminary information on their long-term trends and comparison with model simulation for the different stations. The scope of the present paper is also to provide the necessary suite of information, including data provision procedures, quality control and analysis, data policy, and usage of the ground-based aerosol measurement network. It delivers to users of the World Data Centre on Aerosol, the required confidence in data products in the form of a fully characterized value chain, including uncertainty estimation and requirements for contributing to the global climate monitoring syste
Coal-based reducing agents in ferroalloys and silicon production
No full textManganese, chromium, and silicon ferroalloys are typical examples of alloys that are produced using carbon materials to remove oxygen from the raw materials. A majority of such alloys are currently produced in electric furnaces. The carbon material is chosen based on cost and properties such as content of trace elements and their physical strength. In addition, properties such as CO2 and SiO reactivity may affect the consumption of carbon and energy. Slag reactivity may also affect the quality of the final product, whereas the electrical resistivity of the carbon materials at high temperature will have an effect on the distribution of the temperature in the furnace and the stability of the operation. Finally, the environmental footprint of the operation will be indirectly affected by the carbon materials through CO2, SO2, and trace element emission
Global analysis of continental boundary layer new particle formation based on long-term measurements
Get PDFAtmospheric new particle formation (NPF) is an
important phenomenon in terms of global particle number
concentrations. Here we investigated the frequency of NPF,
formation rates of 10 nm particles, and growth rates in the
size range of 10–25 nm using at least 1 year of aerosol number
size-distribution observations at 36 different locations
around the world. The majority of these measurement sites
are in the Northern Hemisphere. We found that the NPF frequency
has a strong seasonal variability. At the measurement
sites analyzed in this study, NPF occurs most frequently in
March–May (on about 30% of the days) and least frequently
in December–February (about 10% of the days). The median
formation rate of 10 nm particles varies by about 3 orders of
magnitude (0.01–10 cm3 s1) and the growth rate by about
an order of magnitude (1–10 nm h1). The smallest values of
both formation and growth rates were observed at polar sites
and the largest ones in urban environments or anthropogenically
influenced rural sites. The correlation between the NPF
event frequency and the particle formation and growth rate
was at best moderate among the different measurement sites,
as well as among the sites belonging to a certain environmental
regime. For a better understanding of atmospheric NPF
and its regional importance, we would need more observational
data from different urban areas in practically all parts
of the world, from additional remote and rural locations in
North America, Asia, and most of the Southern Hemisphere
(especially Australia), from polar areas, and from at least a
few locations over the ocean
An overview of the first decade of PollyNET: an emerging network of automated Raman-polarization lidars for continuous aerosol profiling
No full textA global vertically resolved aerosol data set covering
more than 10 years of observations at more than 20 measurement
sites distributed from 63 N to 52 S and 72 W to
124 E has been achieved within the Raman and polarization
lidar network PollyNET. This network consists of portable,
remote-controlled multiwavelength-polarization-Raman lidars
(Polly) for automated and continuous 24/7 observations
of clouds and aerosols. PollyNET is an independent,
voluntary, and scientific network. All Polly lidars feature
a standardized instrument design with different capabilities
ranging from single wavelength to multiwavelength systems,
and now apply unified calibration, quality control, and data
analysis. The observations are processed in near-real time
without manual intervention, and are presented online at
polly.tropos.de. The paper gives an overview of the observations
on four continents and two research vessels obtained
with eight Polly systems. The specific aerosol types at these
locations (mineral dust, smoke, dust-smoke and other dusty
mixtures, urban haze, and volcanic ash) are identified by
their Ångström exponent, lidar ratio, and depolarization ratio.
The vertical aerosol distribution at the PollyNET locations
is discussed on the basis of more than 55 000 automatically
retrieved 30 min particle backscatter coefficient profiles at
532 nm as this operating wavelength is available for all Polly
lidar systems. A seasonal analysis of measurements at selected
sites revealed typical and extraordinary aerosol conditions
as well as seasonal differences. These studies show the
potential of PollyNET to support the establishment of a global
aerosol climatology that covers the entire troposphere
Submicrometer aerosols and excess CO as tracers for biomass burning air mass transport over southern Africa
No full textThis paper links surface measurements of biomass burning aerosols and trace gases with
trajectory analysis to determine transport pathways for air masses with high and low concentrations. We
interpret the long-term atmospheric monitoring record from a remote monitoring station in central southern
Africa (North West Province, South Africa). Trace gas analyzers and a Differential Mobility Particle Sizer were
used to measure ground level trace gas and submicron aerosol concentrations. Fire signatures were
identified based on excess CO above average tropospheric levels, and episodes of enhanced particulate
matter concentrations in the 10 to 840 nm size range. Thirty-six biomass burning plumes were reported;
7 had strong signals of excess CO, with ratios between 0.41 and 0.64, while 29 had weak signals ranging
between 0.07 and 0.32. Pathways identifi ed for the long-range transport of biomass burning aerosols were
as follows: easterly (39% frequency), southwesterly (31%), recirculation (22%), and northerly (8%) flow
patterns. CO and Aitken-mode aerosol number strengths were larger for fire emissions arriving in the
easterly and southwesterly air masses than for recirculation and northerly air masses. Easterly and
southwesterly flows were dominated by Aitken-mode aerosol, whereas accumulation-mode particles
dominated in the recirculation and northerly flows. Findings identify biomass burning as a major source
of Aitken-mode aerosols. Enhanced CO concentrations, combined with Aitken- and accumulation-mode
particle number size distributions, are shown to provide a useful signature of plumes originating over
regional biomass combustion event
The composition of ambient and fresh biomass burning aerosols at a savannah site, South Africa
Get PDFAtmospheric aerosols play a key role in climate change, and have adverse effects on human health. Given
South Africa’s status as a rapidly-developing country with increasing urbanisation and industrial growth,
information on the quality of ambient air is important. In this study, the chemical composition of ambient
particles and the particles in fresh biomass burning plumes were studied at a savannah environment in
Botsalano, South Africa. The results showed that Botsalano was regularly affected by air masses that had
passed over several large point sources. Air masses that had passed over the coal-fired Matimba power
station in the Waterberg, or over the platinum group metal smelters in the western Bushveld Igneous Complex,
contained high sulfate concentrations in the submicron ranges. These concentrations were 14 to 37 times
higher compared with air masses that had passed only over rural areas. Because of the limited nature of this
type of data in literature for the interior regions of southern Africa, our report serves as a valuable reference
for future studies. In addition, our biomass burning study showed that potassium in the fresh smoke of
burning savannah grass was likely to take the form of KCl. Clear differences were found in the ratios for
potassium and levoglucosan in the smouldering and flaming phases. Our findings highlight the need for more
comprehensive chamber experiments on various fuel types used in southern Africa, to confirm the ratio of
important biomass burning tracer species that can be used in source apportionment studies in the futur
Observations of ozone formation in southern African savanna and grassland fire plumes
No full textOpen biomass burning is one of the largest sources of aerosols and reactive trace gases into the atmosphere, having a significant effect on earth's radiative budget and air quality. Biomass burning degrades air quality by increasing both particulate matter and ozone levels. Unlike aerosols, ozone is not directly emitted in fires but it is frequently formed in ageing plumes. This is not surprising, as many of the reactive trace gases emitted in biomass burning including nitrogen oxides, carbon monoxide and volatile organic compounds, act as precursors for ozone formation. Geographically, Africa is the most significant source region of biomass burning emissions. Here, we report rapid ozone formation in daytime savanna and grassland fire plumes observed in South Africa. We observed higher ozone production in more flaming cases for plumes fresher than 1.5h. However, in plumes aged >1.5h combustion characteristics have no effect, but ozone production is positively correlated with nitrogen oxides. Furthermore, the plumes with highest ozone production also had the strongest secondary aerosol formation during plume ageing. Additionally, we report emission factors of nitric oxide and sulphur dioxide for southern African savanna and grassland fires. SO2 emission factor was on average 1.1 g kg−1, which is two to three times higher than previous observations for savanna and grassland. On the other hand, the average NO emission factor (2.6 g kg−1) agrees well with previous observation
Observing continental boundary-layer structure and evolution over the South African savannah using a ceilometer
No full textThe atmospheric boundary layer (BL) is the atmospheric layer coupled to the Earth’s surface at relatively short timescales. A key quantity is the BL depth, which is important in many applied areas of weather and climate such as air-quality forecasting. Studying BLs in climates and biomes across the globe is important, particularly in the under-sampled southern hemisphere. The present study is based on a grazed grassland-savannah area in northwestern South Africa during October 2012–August 2014. Ceilometers are probably the cheapest method for measuring continuous aerosol profiles up to several kilometers above ground and are thus an ideal tool for long-term studies of BLs. A ceilometer-estimated BL depth is based on profiles of attenuated backscattering coefficients from atmospheric aerosols; the sharpest drop often occurs at BL top. Based on this, we developed a new method for layer detection that we call the signal-limited layer method. The new algorithm was applied to ceilometer profiles which thus classified BL into classic regime types: daytime convective mixing, and a double layer at night of surface-based stable with a residual layer above it. We employed wavelet fitting to increase successful BL estimation for noisy profiles. The layer-detection algorithm was supported by an eddy-flux station, rain gauges, and manual inspection. Diurnal cycles were often clear, with BL depth detected for 50% of the daytime typically being 1–3 km, and for 80% of the night-time typically being a few hundred meters. Variability was also analyzed with respect to seasons and years. Finally, BL depths were compared with ERA-Interim estimates of BL depth to show reassuring agreemen
Temporal and source assessments of organic and elemental carbon at sites in the northern South African interior
No full textParticulate matter (PM) can affect climate, air quality, human health, acid deposition and visibility, and contain a significant fraction of organic (OC) and elemental carbon (EC). Southern Africa is an important source region for OC and EC, however, little OC and EC data have been published for this region. This paper presents a multi-year, multi-site (an urban-industrial site in the Vaal Triangle, UI-VT; an industrially influenced site at Amerfoort, iI-AF; and two regional background sites at Skukuza and Louis Trichardt, RR-SK and RR-LT) PM with an aerodynamic diameter ≤ 2.5 μm (PM2.5) OC and EC dataset for South Africa. The median OC (9.3) and EC (3.2 μg.m−3) concentrations at UI-VT were 1.3 to 2.5 and 2.7 to 4.4 times higher, if compared to the other sites. OC/EC ratios indicated that sources in close proximity to UI-VT were likely the main contributors, while sources that are more distant contributed fractionally more at the other sites. Household combustion for space heating and regional open biomass burning contributed to elevated levels during the cold and dry months at UI-VT. Regional open biomass burning also lead to higher OC and EC concentrations during the dry season at the industrially influenced site (iI-AF) and one of the regional background sites (RR-SK). From the seasonal concentration patterns, it seemed as if household combustion for space heating also contributed at these two sites during the cold months, but this could not be proven, even if only samples with limited influence of open biomass burning were considered. Such biomass burning influences were semi-quantified by considering MODIS fire pixels occurring within the air mass fetch region for each sample. For the remaining regional background site (RR-LT) the results suggesed that only regional open biomass burning contributed to elevated levels of OC and EC in the dry season and that household combustion for space heating did not contribute significantl
Modelling new particle formation events in the South African savannah
Get PDFAfrica is one of the less studied continents with respect to atmospheric aerosols. Savannahs are complex
dynamic systems sensitive to climate and land-use changes, but the interaction of these systems with the
atmosphere is not well understood. Atmospheric particles, called aerosols, affect the climate on regional
and global scales, and are an important factor in air quality. In this study, measurements from a relatively
clean savannah environment in South Africa were used to model new particle formation and growth. There
already are some combined long-term measurements of trace gas concentrations together with aerosol and
meteorological variables available, but to our knowledge this is the first detailed simulation that includes
all the main processes relevant to particle formation. The results show that both of the particle formation
mechanisms investigated overestimated the dependency of the formation rates on sulphuric acid. From
the two particle formation mechanisms tested in this work, the approach that included low volatile organic
compounds to the particle formation process was more accurate in describing the nucleation events than the
approach that did not. To obtain a reliable estimate of aerosol concentration in simulations for larger scales,
nucleation mechanisms would need to include organic compounds, at least in southern Africa. This work
is the first step in developing a more comprehensive new particle formation model applicable to the unique
environment in southern Africa. Such a model will assist in better understanding and predicting new particle
formation – knowledge which could ultimately be used to mitigate impacts of climate change and air qualityFinnish Center of Excellence in Physics,
Chemistry, Biology and Meteorology of Atmospheric Composition and
Climate Change, Helsinki University Centre for Environment (HENVI).
The CSC–IT Center for Science Lt
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