16 research outputs found
Multi-model study of mercury dispersion in the atmosphere: vertical and interhemispheric distribution of mercury species
Atmospheric chemistry and transport of mercury play a key role in the global mercury cycle. However, there are still considerable knowledge gaps concerning the fate of mercury in the atmosphere. This is the second part of a model intercomparison study investigating the impact of atmospheric chemistry and emissions on mercury in the atmosphere. While the first study focused on ground-based observations of mercury concentration and deposition, here we investigate the vertical and interhemispheric distribution and speciation of mercury from the planetary boundary layer to the lower stratosphere. So far, there have been few model studies investigating the vertical distribution of mercury, mostly focusing on single aircraft campaigns. Here, we present a first comprehensive analysis based on various aircraft observations in Europe, North America, and on intercontinental flights.
The investigated models proved to be able to reproduce the distribution of total and elemental mercury concentrations in the troposphere including interhemispheric trends. One key aspect of the study is the investigation of mercury oxidation in the troposphere. We found that different chemistry schemes were better at reproducing observed oxidized mercury patterns depending on altitude. High concentrations of oxidized mercury in the upper troposphere could be reproduced with oxidation by bromine while elevated concentrations in the lower troposphere were better reproduced by OH and ozone chemistry. However, the results were not always conclusive as the physical and chemical parameterizations in the chemistry transport models also proved to have a substantial impact on model results
The impact of the chemical production of methyl nitrate from the NO + CH3O2 reaction on the global distributions of alkyl nitrates, nitrogen oxides and tropospheric ozone: a global modelling study
The impact of the chemical production of methyl nitrate from the NO + CH3O2 reaction on the global distributions of alkyl nitrates, nitrogen oxides and tropospheric ozone: a global modelling study
NO and NOy in the upper troposphere: Nine years of CARIBIC measurements onboard a passenger aircraft
Nitrogen oxide (NO and NOy) measurements were performed onboard an in-service aircraft within the
framework of CARIBIC (Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument
Container). A total of 330 flights were completed from May 2005 through April 2013 between
Frankfurt/Germany and destination airports in Canada, the USA, Brazil, Venezuela, Chile, Argentina,
Colombia, South Africa, China, South Korea, Japan, India, Thailand, and the Philippines. Different regions
show differing NO and NOy mixing ratios. In the mid-latitudes, observed NOy and NO generally shows
clear seasonal cycles in the upper troposphere with a maximum in summer and a minimum in winter.
Mean NOy mixing ratios vary between 1.36 nmol/mol in summer and 0.27 nmol/mol in winter. Mean NO
mixing ratios range between 0.05 nmol/mol and 0.22 nmol/mol. Regions south of 40°N show no
consistent seasonal dependence. Based on CO observations, low, median and high CO air masses were
defined. According to this classification, more data was obtained in high CO air masses in the regions
south of 40°N compared to the midlatitudes. This indicates that boundary layer emissions are more
important in these regions. In general, NOy mixing ratios are highest when measured in high CO air
masses. This dataset is one of the most comprehensive NO and NOy dataset available today for the upper
troposphere and is therefore highly suitable for the validation of atmosphere-chemistry-models
Preparation and antifouling properties of PVDF ultrafiltration membranes with polyaniline (PANI) nanofibers and hydrolysed PSMA (H-PSMA) as additives
Polyaniline (PANI) nanofibers were used as hydrophilic additives to study their effect on the performance of polyvinylidene fluoride (PVDF) ultrafiltration (UF) membranes. PVDF UP membranes were prepared by the phase inversion method with hydrolyzed polystyrene-co-maleic anhydride (H-PSMA) and PANI nanofibers as additives. PANI nanofibers were synthesized by rapid mixing reaction and were used as a hydrophilic modifying agent with varying concentrations (0-1.5 wt.%) in the membranes. The synthesized PANI nanofibers were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM) analysis. Hydrolyzed PSMA was prepared by the hydrolysis of PSMA and was used as a novel pore forming additive. The addition of PANI nanofibers into the membranes increased the membrane hydrophilicity, porosity, water uptake and permeability. The membranes also showed good antifouling nature during BSA (bovine serum albumin) filtration when compared to the pristine membrane without PANI nanofibers. Membrane with 1.0 wt.% PANI content showed highest permeability among the synthesized membranes. The membrane having highest permeability was subjected to heavy metal ion rejection which showed high rejection of 98.52% and 9738% for heavy metal ions Pb2+ and Cd2+ respectively
NO- and NOy Measurements - A New Contribution to the CARIBIC Observations; Instrumental Set-Up and First Measurements
Origin of aerosol particles in the mid-latitude and subtropical upper troposphere and lowermost stratosphere from cluster analysis of CARIBIC data
The origin of aerosol particles in the upper troposphere
and lowermost stratosphere over the Eurasian continent
was investigated by applying cluster analysis methods
to in situ measured data. Number concentrations of submicrometer
aerosol particles and trace gas mixing ratios derived
by the CARIBIC (Civil Aircraft for Regular Investigation
of the Atmosphere Based on an Instrument Container) measurement
system on flights between Germany and South-East
Asia were used for this analysis. Four cluster analysis methods
were applied to a test data set and their capability of separating
the data points into scientifically reasonable clusters
was assessed. The best method was applied to seasonal data
subsets for summer and winter resulting in five cluster or air
mass types: stratosphere, tropopause, free troposphere, high
clouds, and boundary layer influenced. Other source clusters,
like aircraft emissions could not be resolved in the present
data set with the used methods. While the cluster separation
works satisfactory well for the summer data, in winter interpretation
is more difficult, which is attributed to either different
vertical transport pathways or different chemical lifetimes
in both seasons. The geographical distribution of the
clusters together with histograms for nucleation and Aitken
mode particles within each cluster are presented. Aitken
mode particle number concentrations show a clear vertical
gradient with the lowest values in the lowermost stratosphere
(750�2820 particles/cm3 STP, minimum of the two 25% �
and maximum of the two 75%-percentiles of both seasons)
and the highest values for the boundary-layer-influenced air
(4290�22 760 particles/cm3 STP). Nucleation mode particles
are also highest in the boundary-layer-influenced air (1260�
29 500 particles/cm3 STP), but are lowest in the free troposphere
(0�450 particles/cm3 STP). The given submicrometer
particle number concentrations represent the first large-scale
seasonal data sets for the upper troposphere and lowermost
stratosphere over the Eurasian continen