The review discusses the potential relationship between hypoxia resistance and longevity, the influence of carbon dioxide on the mechanisms of aging of the mammalian organism, and intermittent ...hypercapnic–hypoxic effects on the signaling pathways of aging mechanisms. In the article, we focused on the potential mechanisms of the gero-protective efficacy of carbon dioxide when combined with hypoxia. The review summarizes the possible influence of intermittent hypoxia and hypercapnia on aging processes in the nervous system. We considered the perspective variants of the application of hypercapnic–hypoxic influences for achieving active longevity and the prospects for the possibilities of developing hypercapnic–hypoxic training methods.
Measurements of the fraction of contemporary carbon (
f
C) in organic carbon (OC) of ambient aerosols are presented using radiocarbon (
14C). This value directly represents the biogenic contribution ...to OC, as the biosphere releases organic compounds with the present
14C/
12C level (
f
C=1), whereas
14C has become extinct in anthropogenic emissions of fossil carbon (
f
C=0). This simple model assumes biomass burning to be negligible. Daytime and nighttime samples were collected at an urban location in Zürich (Switzerland) in August 2002. Measured
f
C values ranged from 0.51 to 0.80, which indicates a major biogenic influence. This demonstrates that carbonaceous aerosol at this site is more dominated by the rural vicinity of Zürich rather than direct urban sources. Furthermore, this investigation enabled an insight into the processes of particle formation, accumulation, and deposition for biogenic and anthropogenic emission sources. On the one hand, biogenic OC depends on the activity of plants to emit reactive volatile species like monoterpenes and on atmospheric oxidants that promote secondary organic aerosol formation. On the other hand, anthropogenic OC correlates with black carbon or elemental carbon.
Aerosol samples were collected in Zurich, Switzerland, at an urban background site and were analyzed with size exclusion chromatography (SEC) and laser/desorption ionization mass spectrometry ...(LDI‐MS) for water‐soluble organic compounds with high molecular weight. Daily samples were collected during two campaigns in winter and summer, for 1 month each. The concentration of high‐molecular‐weight compounds (humic‐like substances (HULIS)) was between 0.4 and 4 μg/m3 in winter and summer. The most intense signals in the LDI‐MS mass spectra were measured between m/z150 and 500, comparing well with the mode of the two main high mass peaks determined with SEC corresponding to masses between 200 and 600 Da. For the maximum molecular weight, however, different results were obtained by the two techniques: whereas a maximum molecular weight between 1300 and 3300 Da was found with SEC, hardly any peaks above m/z700 were measured with LDI‐MS. During summer the maximum molecular weight of HULIS (determined with SEC) correlates positively with several parameters such as ozone and increased temperature indicative of enhanced atmospheric photo‐oxidation. The HULIS concentration also correlates positively with the oxalic acid concentration in the particles. This suggests that HULIS are generated by secondary processes in summer. The lack of such correlations during winter suggests that other sources and processes might be important during colder seasons.
We present results from two field deployments of a unique tandem differential mobility analyzer (TDMA) configuration with two primary capabilities: identifying alternative stable or meta-stable ...ambient aerosol hydration states associated with hysteresis in aerosol hydration behavior and determining the actual Ambient hydration State (AS-TDMA). This data set is the first to fully classify the ambient hydration state of aerosols despite recognition that hydration state significantly impacts the roles of aerosols in climate, visibility and heterogeneous chemistry. The AS-TDMA was installed at a site in eastern Tennessee on the border of Great Smoky Mountains National Park for projects during the summer of 2006 and winter of 2007–2008. During the summer, 12% of the aerosols sampled in continuous AS-TDMA measurements were found to posses two possible hydration states under ambient conditions. In every case, the more hydrated of the possible states was occupied. The remaining 88% did not posses multiple possible states. In continuous measurements during the winter, 49% of the aerosols sampled possessed two possible ambient hydration states; the remainder possessed only one. Of those aerosols with multiple possible ambient hydration states, 65% occupied the more hydrated state; 35% occupied the less hydrated state. This seasonal contrast is supported by differences in the fine particulate (PM2.5) composition and ambient RH as measured during the two study periods. In addition to seasonal summaries, this work includes case studies depicting the variation of hydration state with changing atmospheric conditions.
Fresh and atmospherically aged
biomass-burning (BB) aerosol mass is mostly comprised of strongly
light-absorbing black carbon (BC) and of organic carbon (OC) with its
light-absorbing fraction – brown ...carbon (BrC). There is a lack of data on
the physical and chemical properties of atmospheric BB aerosols, leading to
high uncertainties in estimates of the BB impact on air quality and climate,
especially for BrC. The polarity of chemical compounds influences their fate
in the atmosphere including wet/dry deposition and chemical and physical
processing. So far, most of the attention has been given to the water-soluble
(polar) fraction of BrC, while the non-polar BrC fraction has been largely
ignored. In the present study, the light absorption properties of polar and
non-polar fractions of fresh and aged BB emissions were examined to estimate
the contribution of different-polarity organic compounds to the light
absorption properties of BB aerosols. In our experiments, four globally and regionally important fuels were burned
under flaming and smoldering conditions in the Desert Research Institute
(DRI)
combustion chamber. To mimic atmospheric oxidation processes (5–7 days), BB
emissions were aged using an oxidation flow reactor (OFR). Fresh and OFR-aged
BB aerosols were collected on filters and extracted with water and hexane to
study absorption properties of polar and non-polar organic species. Results
of spectrophotometric measurements (absorption weighted by the solar spectrum
and normalized to mass of fuel consumed) over the 190 to 900 nm wavelength
range showed that the non-polar (hexane-soluble) fraction is 2–3 times more
absorbing than the polar (water-soluble) fraction. However, for emissions
from fuels that undergo flaming combustion, an increased absorbance was
observed for the water extracts of oxidized/aged emissions while the
absorption of the hexane extracts was lower for the aged emissions for the
same type of fuels. Absorption Ångström exponent (AAE) values,
computed based on absorbance values from spectrophotometer measurements, were
changed with aging and the nature of this change was fuel dependent. The
light absorption by humic-like substances (HULIS) was found to be higher in fuels characteristic of the
southwestern USA. The absorption of the HULIS fraction was lower for OFR-aged
BB emissions. Comparison of the light absorption properties of
different-polarity extracts (water, hexane, HULIS) provides insight into the
chemical nature of BB BrC and its transformation during oxidation processes.
The surface air warming over the Arctic has been almost twice as much as the global average in recent decades. In this region, unprecedented amounts of smoldering peat fires have been identified as a ...major emission source of climate-warming agents. While much is known about greenhouse gas emissions from these fires, there is a knowledge gap on the nature of particulate emissions and their potential role in atmospheric warming. Here, we show that aerosols emitted from burning of Alaskan and Siberian peatlands are predominantly brown carbon (BrC) – a class of visible light-absorbing organic carbon (OC) – with a negligible amount of black carbon content. The mean fuel-based emission factors for OC aerosols ranged from 3.8 to 16.6 g kg−1. Their mass absorption efficiencies were in the range of 0.2–0.8 m2 g−1 at 405 nm (violet) and dropped sharply to 0.03–0.07 m2 g−1 at 532 nm (green), characterized by a mean Ångström exponent of ≈ 9. Electron microscopy images of the particles revealed their morphologies to be either single sphere or agglomerated “tar balls”. The shortwave top-of-atmosphere aerosol radiative forcing per unit optical depth under clear-sky conditions was estimated as a function of surface albedo. Only over bright surfaces with albedo greater than 0.6, such as snow cover and low-level clouds, the emitted aerosols could result in a net warming (positive forcing) of the atmosphere.
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