550 research outputs found
Chemical evolution of primary and formation of secondary biomass burning aerosols during daytime and nighttime
Organic matter (OM) can constitute more than half of
fine particulate matter (PM) and affect climate and
human health. Natural and man-made biomass burning
is an important contributor to primary and secondary
OM (POA and SOA) with an increasing trend.
Aerosol mass spectrometry (AMS) and Fourier
transform infrared spectroscopy (FTIR) are two
complementary methods of identifying the complex
chemical composition of OM in terms of mass fragments
and functional groups, respectively. AMS offers a
relatively higher temporal resolution compared to FTIR
(performed on PTFE filters). However, the interpretation
of AMS mass spectra remains complicated due to the
extensive molecular fragmentation.
In this study, we used collocated AMS and FTIR
measurements to better understand the evolution of
biomass burning POA and SOA due to different
mechanisms of chemical aging (e.g., homogeneous gasphase
oxidation and heterogeneous reactions). Primary
emissions from wood and pellet stoves were injected
into a 10 m3 environmental chamber located at the
Center for Studies of Air Qualities and Climate Change (CSTACC)
at ICE-HT/FORTH. Primary emissions were aged
using hydroxyl and nitrate radicals with atmospherically
relevant exposures. PM1 was analyzed by a highresolution
time-of-flight (HR-ToF) and was also collected
on PTFE filters over 20-minute periods before and after
aging for off-line FTIR analysis.
AMS and FTIR measurements agreed well with
regards to the concentration of OM and some biomass
burning tracers (levoglucosan and lignin; Yazdani A.,
2020b) and the OM:OC ratio. Chamber wall loss rates
were estimated using AMS OM concentration and were
used to split the contribution of POA and SOA. The
estimated FTIR and AMS spectra of SOA produced by
reactions of biomass burning volatile organic compounds
(VOCs) with OH were found to have prominent acid
signatures. Organonitrates, on the other hand, appeared
to be important for SOA produced by the nitrate radical.
We found that with continued aging, SOA evolves and
becomes similar to the oxygenated OA (OOA) in the
atmosphere. We also found that POA composition also
evolves with aging. Our estimates show that up to 10 %
of POA mass undergoes aging. Biomass burning tracers
such as lignin and levoglucosan in addition to
hydrocarbons are among the POA compounds that are
lost the most in biomass burning POA (up to 6 times more
than OM decrease due to chamber wall losses; Fig. 1).
This diminution is observed for both semi-volatile
(levoglucosan and hydrocarbons) and non-volatile
(lignin) POA species, implying the importance of gasparticle
partitioning, heterogeneous reactions, and
photolysis for POA evolution in the atmosphere. This
result can be important since chemical transport models
usually do not consider POA heterogeneous reactions.
Figure 1. Trends of individual AMS mass fragments (with
contribution to OM> 0.3 %) during aging with UV
(starting from time zero). All mass fragments have been
normalized by their concentration before the with start
of aging and corrected for the chamber wall losses.
Important mass fragments are shown in color.
This work was supported by the project PyroTRACH (ERC-
2016-COG) funded from H2020-EU.1.1. - Excellent
Science - European Research Council (ERC), project ID
726165 and funding from the Swiss National Science
Foundation (200021_172923).
References
Yazdani, A., Dudani, N., Takahama, S., Bertrand, A.,
Prévôt, A. S. H., El Haddad, I., and Dillner, A. M.:
Characterization of Primary and Aged Wood Burning and
Coal Combustion Organic Aerosols in Environmental
Chamber and Its Implications for Atmospheric Aerosols,
Atmospheric Chemistry and Physics Discussions, pp. 1–
32
Differentiating between primary and secondary organic aerosols of biomass burning in an environmental chamber with FTIR and AMS
Fine particulate matter (PM) affects visibility, climate and public health. Organic matter (OM), which is hard to characterize due to its complex chemical composition, can constitute more than half of the PM. Biomass burning from residential wood burning, wildfires, and prescribed burning is a major source of OM with an ever-increasing importance.
Aerosol mass spectrometry (AMS) and Fourier transform infrared spectroscopy (FTIR) are two complementary methods of identifying the chemical composition of OM. AMS measures the bulk composition of OM with relatively high temporal resolution but provides limited parent compound information. FTIR, carried out on samples collected on Teflon filters, provides detailed functional groupinformation at the expense of relatively low temporal resolution.
In this study, we used these two methods to better understand the evolution of biomass burning OM in the atmosphere with aging. For this purpose, primary emissions from wood and pellet stoves were injected into the Center for Studies of Air Qualities and Climate Change (C-STACC) environmental chamber at ICE-HT/FORTH. Primary emissions were aged using hydroxyl and nitrate radicals (with atmospherically relevant exposures) simulating atmospheric day-time and night-time oxidation. A time-of-flight (ToF) AMS reported the composition of non-refractory PM1 every three minutes and PM1 was collected on PTFE filters over 20-minute periods before and after aging for off-line FTIR analysis.
We found that AMS and FTIR measurements agreed well in terms of measured OM mass concentration, the OM:OC ratio, and concentration of biomass burning tracers – lignin and levoglucosan. AMS OM concentration was used to estimate chamber wall loss rates which were then used separate the contribution of primary and secondary organic aerosols (POA and SOA) to the aged OM. AMS mass spectra and FTIR spectra of biomass burning SOA and estimates of bulk composition were obtained by this procedure. FTIR and AMS spectra of SOA produced by OH oxidation of biomass burning volatile organic compounds (VOCs) were dominated by acid signatures. Organonitrates, on the other hand, appeared to be important in the SOA aged by the nitrate radical. The spectra from the two instruments also indicated that the signatures of certain compounds such as levoglucosan, lignin and hydrocarbons, which are abundant in biomass burning POA, diminish with aging significantly more than what can be attributed to chamber wall losses. The latter suggests biomass burning POA chemical composition might change noticeably due to heterogeneous reactions or partitioning in the atmosphere. Therefore, the common assumption of stable POA composition is only partially true. In addition, more stable biomass burning tracers should be used to be able to identify highly aged biomass burning aerosols in the atmosphere
Chemical evolution of primary and secondary biomass burning aerosols during daytime and nighttime
Primary emissions from wood and pellet stoves were aged in an atmospheric simulation chamber under daytime and nighttime conditions. The aerosol was analyzed with the online Aerosol Mass Spectrometer (AMS) and offline Fourier transform infrared spectroscopy (FTIR). Measurements using the two techniques agreed reasonably well in terms of the organic aerosol (OA) mass concentration, OA:OC trends, and concentrations of biomass burning markers – lignin-like compounds and anhydrosugars. Based on the AMS, around 15 % of the primary organic aerosol (POA) mass underwent some form of transformation during daytime oxidation conditions after 6–10 hours of atmospheric exposure. A lesser extent of transformation was observed during the nighttime oxidation. The decay of certain semi-volatile (e.g., levoglucosan) and less volatile (e.g., lignin-like) POA components was substantial during aging, highlighting the role of heterogeneous reactions and gas-particle partitioning. Lignin-like compounds were observed to degrade under both daytime and nighttime conditions, whereas anhydrosugars degraded only under daytime conditions. Among the marker mass fragments of primary biomass burning OA (bbPOA), heavy ones (higher m/z) were relatively more stable during aging. The biomass burning secondary OA (bbSOA) became more oxidized with continued aging and resembled those of aged atmospheric organic aerosols. The bbSOA formed during daytime oxidation was dominated by acids. Organonitrates were an important product of nighttime reactions in both humid and dry conditions. Our results underline the importance of changes to both the primary and secondary biomass burning aerosols during their atmospheric aging. Heavier AMS fragments seldomly used in atmospheric chemistry can be used as more stable tracers of bbPOA and in combination with the established levoglucosan marker, can provide an indication of the extent of bbPOA aging
The RhoA transcriptional program in pre-T cells
The GTPase RhoA is essential for the development of pre-T cells in the thymus. To investigate the mechanisms used by RhoA to control thymocyte development we have used Affymetrix gene profiling to identify RhoA regulated genes in T cell progenitors. The data show that RhoA plays a specific and essential role in pre-T cells because it is required for the expression of transcription factors of the Egr-1 and AP-1 families that have critical functions in thymocyte development. Loss of RhoA function in T cell progenitors causes a developmental block that pheno-copies the consequence of losing pre-TCR expression in Recombinase gene 2 (Rag2) null mice. Transcriptional profiling reveals both common and unique gene targets for RhoA and the pre-TCR indicating that RhoA participates in the pre-TCR induced transcriptional program but also mediates pre-TCR independent gene transcription
Influence of crustal dust and sea spray supermicron particle concentrations and acidity on inorganic NO_3^- aerosol during the 2013 Southern Oxidant and Aerosol Study
Inorganic aerosol composition was measured in the southeastern United States, a region that exhibits high aerosol mass loading during the summer, as part of the 2013 Southern Oxidant and Aerosol Study (SOAS) campaign. Measurements using a Monitor for AeRosols and GAses (MARGA) revealed two periods of high aerosol nitrate (NO_^3−) concentrations during the campaign. These periods of high nitrate were correlated with increased concentrations of supermicron crustal and sea spray aerosol species, particularly Na^+ and Ca^(2+), and with a shift towards aerosol with larger (1 to 2.5 μm) diameters. We suggest this nitrate aerosol forms by multiphase reactions of HNO_3 and particles, reactions that are facilitated by transport of crustal dust and sea spray aerosol from a source within the United States. The observed high aerosol acidity prevents the formation of NH_4NO_3, the inorganic nitrogen species often dominant in fine-mode aerosol at higher pH. Calculation of the rate of the heterogeneous uptake of HNO_3 on mineral aerosol supports the conclusion that aerosol NO_3^− is produced primarily by this process, and is likely limited by the availability of mineral cation-containing aerosol surface area. Modeling of NO_3^− and HNO_3 by thermodynamic equilibrium models (ISORROPIA II and E-AIM) reveals the importance of including mineral cations in the southeastern United States to accurately balance ion species and predict gas–aerosol phase partitioning
Widefield fluorescence imaging as an auxiliary tool to select the biopsy site for actinic cheilitis diagnosis
Actinic cheilitis (AC) is considered a potentially malignant disorder that mainly affects the lower lip, and it is caused by prolonged sun exposure. Clinical diagnosis relies on visual inspection by a trained clinician, when suspected of dysplasia changes, a biopsy is required. The heteregenous characteristics of the AC, makes the choice of the biopsy site a difficult task. Fluorescence detection has been presented as a useful tool to to detect biochemical and morphological tissue features related to cancer diagnosis, but still its effectiveness to discriminate premalignant lesion is not completely defined. In this clinical study, 57 AC patients were investigated using widefield fluorescence imaging (WFI) to evaluate the efficacy of this technique as an auxiliary tool to biopsy site location. A handheld fluorescence system based on 400-450 nm LED illumination Distinct trained clinicians evaluate the patient either with the conventional examination or the WFI, and were blinded to the other evaluation. A biopsy site was chosen based on the clinical examination, and another site was chosen using the fluorescence visualization. A total of 114 punch biopsies were performed, and 93% of the tissue samples presented epithelial dysplasia. The majority of the sites that presented moderate or severe dysplasia were sites chosen by WFI, showing its efficiency to improve the diagnosis of AC.CNPq (475322/2011-8)CEPID-CePOF/FAPESP (98/14270-8
Phosphoinositide-dependent kinase 1 controls migration and malignant transformation but not cell growth and proliferation in PTEN-null lymphocytes
In normal T cell progenitors, phosphoinositide-dependent kinase l (PDK1)–mediated phosphorylation and activation of protein kinase B (PKB) is essential for the phosphorylation and inactivation of Foxo family transcription factors, and also controls T cell growth and proliferation. The current study has characterized the role of PDK1 in the pathology caused by deletion of the tumor suppressor phosphatase and tensin homologue deleted on chromosome 10 (PTEN). PDK1 is shown to be essential for lymphomagenesis caused by deletion of PTEN in T cell progenitors. However, PTEN deletion bypasses the normal PDK1-controlled signaling pathways that determine thymocyte growth and proliferation. PDK1 does have important functions in PTEN-null thymocytes, notably to control the PKB–Foxo signaling axis and to direct the repertoire of adhesion and chemokine receptors expressed by PTEN-null T cells. The results thus provide two novel insights concerning pathological signaling caused by PTEN loss in lymphocytes. First, PTEN deletion bypasses the normal PDK1-controlled metabolic checkpoints that determine cell growth and proliferation. Second, PDK1 determines the cohort of chemokine and adhesion receptors expressed by PTEN-null cells, thereby controlling their migratory capacity
Stability assessment of organic sulfur and organosulfate compounds in filter samples for quantification by Fourier- transform infrared spectroscopy
Organic sulfur and sulfate compounds, which are tracers for sources and
atmospheric processes, are not currently measured in national monitoring
networks such as the Interagency Monitoring of Protected Visual Environments
(IMPROVE). The goal of this paper is to begin to assess the stability of
organic sulfur and sulfate-containing compounds on polytetrafluoroethylene
(PTFE) filters and the suitability of Fourier-transform infrared (FT-IR)
spectroscopy to measure these compounds. Stability assessment is needed
because PTFE samples collected by IMPROVE are typically stored 6–9 months
prior to analysis. For this study, two organosulfur compounds,
methanesulfonic acid (MSA) and hydroxymethanesulfonate ion (HMS), and two
organosulfate compounds, methyl sulfate (MS) and 2-methyltetrol sulfate
(2-MTS), are collected individually on PTFE filters. Gravimetric mass
measurements are used to assess mass stability over time. FT-IR spectra are
evaluated to assess the capability of measuring the compound from PTFE
filters by assessing the compound stability or chemical changes over time.
Ion chromatography (IC) and inductively coupled plasma optical emission
spectroscopy (ICP-OES) are used as additional tools to assess stability or
chemical changes over time. MS has the highest potential to be measured by
FT-IR in IMPROVE samples. For MS, a simple organosulfate, the mass changes
are within measurement uncertainty and FT-IR spectra indicate no
compositional change over a 4-month period, suggesting that MS can be measured
using FT-IR. IC and ICP-OES support the conclusion that MS is stable on the
filter. However, for 2-MTS, the other organosulfate measured in this study,
spectral changes after a month on the filter suggest that it decomposes into
other organosulfates or an inorganic sulfate. MSA in IMPROVE samples can be
measured, but only as a lower bound, due to volatility off the filter as
indicated by FT-IR and gravimetry. FT-IR and IC both show that MSA does not
chemically change over the course of the study. Measurements by all
methods indicate that HMS is unstable on the PTFE filter, and IC and FT-IR indicate
that it likely converts to inorganic sulfate. Future work includes the
evaluation of these compounds in an ambient aerosol sample matrix to
determine any differences in stability, identifying interference that could
limit quantification, and developing calibrations to measure the compounds or
functional groups in ambient samples.</p
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