We present results from a high-resolution chemical ionization time-of-flight mass spectrometer (HRToF-CIMS), operated with two different thermal desorption inlets, designed to characterize the gas ...and aerosol composition. Data from two field campaigns at forested sites are shown. Particle volatility distributions are estimated using three different methods: thermograms, elemental formulas, and measured partitioning. Thermogram-based results are consistent with those from an aerosol mass spectrometer (AMS) with a thermal denuder, implying that thermal desorption is reproducible across very different experimental setups. Estimated volatilities from the detected elemental formulas are much higher than from thermograms since many of the detected species are thermal decomposition products rather than actual SOA molecules. We show that up to 65% of citric acid decomposes substantially in the FIGAERO–CIMS, with ∼20% of its mass detected as gas-phase CO2, CO, and H2O. Once thermal decomposition effects on the detected formulas are taken into account, formula-derived volatilities can be reconciled with the thermogram method. The volatility distribution estimated from partitioning measurements is very narrow, likely due to signal-to-noise limits in the measurements. Our findings indicate that many commonly used thermal desorption methods might lead to inaccurate results when estimating volatilities from observed ion formulas found in SOA. The volatility distributions from the thermogram method are likely the closest to the real distributions.
Secondary organic aerosol (SOA) is formed from the atmospheric oxidation of gas-phase organic compounds leading to the formation of particle mass. Gasoline- and diesel-powered motor vehicles, both ...on/off-road, are important sources of SOA precursors. They emit complex mixtures of gas-phase organic compounds that vary in volatility and molecular structurefactors that influence their contributions to urban SOA. However, the relative importance of each vehicle type with respect to SOA formation remains unclear due to conflicting evidence from recent laboratory, field, and modeling studies. Both are likely important, with evolving contributions that vary with location and over short time scales. This review summarizes evidence, research needs, and discrepancies between top-down and bottom-up approaches used to estimate SOA from motor vehicles, focusing on inconsistencies between molecular-level understanding and regional observations. The effect of emission controls (e.g., exhaust aftertreatment technologies, fuel formulation) on SOA precursor emissions needs comprehensive evaluation, especially with international perspective given heterogeneity in regulations and technology penetration. Novel studies are needed to identify and quantify “missing” emissions that appear to contribute substantially to SOA production, especially in gasoline vehicles with the most advanced aftertreatment. Initial evidence suggests catalyzed diesel particulate filters greatly reduce emissions of SOA precursors along with primary aerosol.
Volatility and viscosity are important properties of organic aerosols (OA),
affecting aerosol processes such as formation, evolution, and partitioning of
OA. Volatility distributions of ambient OA ...particles have often been
measured, while viscosity measurements are scarce. We have previously
developed a method to estimate the glass transition temperature (Tg) of
an organic compound containing carbon, hydrogen, and oxygen. Based on
analysis of over 2400 organic compounds including oxygenated organic
compounds, as well as nitrogen- and sulfur-containing organic compounds, we
extend this method to include nitrogen- and sulfur-containing compounds
based on elemental composition. In addition, parameterizations are developed
to predict Tg as a function of volatility and the atomic
oxygen-to-carbon ratio based on a negative correlation between Tg and
volatility. This prediction method of Tg is applied to ambient
observations of volatility distributions at 11 field sites. The
predicted Tg values of OA under dry conditions vary mainly from 290 to 339 K
and the predicted viscosities are consistent with the results of ambient
particle-phase-state measurements in the southeastern US and the Amazonian
rain forest. Reducing the uncertainties in measured volatility distributions
would improve predictions of viscosity, especially at low relative humidity.
We also predict the Tg of OA components identified via positive matrix
factorization of aerosol mass spectrometer (AMS) data. The predicted viscosity of
oxidized OA is consistent with previously reported viscosity of secondary organic aerosols (SOA) derived
from α-pinene, toluene, isoprene epoxydiol (IEPOX), and diesel fuel.
Comparison of the predicted viscosity based on the observed volatility
distributions with the viscosity simulated by a chemical transport model
implies that missing low volatility compounds in a global model can lead to
underestimation of OA viscosity at some sites. The relation between
volatility and viscosity can be applied in the molecular corridor or
volatility basis set approaches to improve OA simulations in chemical
transport models by consideration of effects of particle viscosity in OA
formation and evolution.
Oxygenated volatile organic compounds (OVOCs) and secondary organic aerosol (SOA) formation potential of ambient air in Guangzhou, China was investigated using a field-deployed oxidation flow reactor ...(OFR). The OFR was used to mimic hours to weeks of atmospheric exposure to hydroxyl (OH) radicals within the 2–3 min residence time. A comprehensive investigation on the variation of VOCs and OVOCs as a function of OH exposure is shown. Substantial formation of organic acids and nitrogen-containing OVOC species were observed. Maximum SOA formation in the OFR was observed following 1–4 equiv days’ OH exposure. SOA produced from known/measured VOC/IVOC precursors such as single-ring aromatics and long-chain alkanes can account for 52–75% of measured SOA under low NO x and 26–60% under high NO x conditions based on laboratory SOA yield parametrizations. To our knowledge, this is the first time that the contribution (8–20%) of long-chain (C8–C20) alkane oxidation to OFR SOA formation was quantified from direct measurement. By additionally estimating contribution from unmeasured semivolatile and intermediate volatility compounds (S/IVOCs) that are committed with C8–C20 alkanes, 64–100% of the SOA formation observed in the OFR can be explained, signifying the important contribution of S/IVOCs such as large cyclic alkanes to ambient SOA.
Evolution of brown carbon in wildfire plumes Forrister, Haviland; Liu, Jiumeng; Scheuer, Eric ...
Geophysical research letters,
16 June 2015, Letnik:
42, Številka:
11
Journal Article
Recenzirano
Odprti dostop
Particulate brown carbon (BrC) in the atmosphere absorbs light at subvisible wavelengths and has poorly constrained but potentially large climate forcing impacts. BrC from biomass burning has ...virtually unknown lifecycle and atmospheric stability. Here, BrC emitted from intense wildfires was measured in plumes transported over 2 days from two main fires, during the 2013 NASA SEAC4RS mission. Concurrent measurements of organic aerosol (OA) and black carbon (BC) mass concentration, BC coating thickness, absorption Ångström exponent, and OA oxidation state reveal that the initial BrC emitted from the fires was largely unstable. Using back trajectories to estimate the transport time indicates that BrC aerosol light absorption decayed in the plumes with a half‐life of 9 to 15 h, measured over day and night. Although most BrC was lost within a day, possibly through chemical loss and/or evaporation, the remaining persistent fraction likely determines the background BrC levels most relevant for climate forcing.
Key Points
Biomass burning brown carbon has unknown lifecycle and atmospheric stability
Brown carbon and aerosol properties from two fires are measured for 50 h
Wildfire brown carbon lifetime was 9–15 h, but a small fraction is stable
Emissions from gasoline and diesel vehicles are predominant anthropogenic sources of reactive gas-phase organic carbon and key precursors to secondary organic aerosol (SOA) in urban areas. Their ...relative importance for aerosol formation is a controversial issue with implications for air quality control policy and public health. We characterize the chemical composition, mass distribution, and organic aerosol formation potential of emissions from gasoline and diesel vehicles, and find diesel exhaust is seven times more efficient at forming aerosol than gasoline exhaust. However, both sources are important for air quality; depending on a region’s fuel use, diesel is responsible for 65% to 90% of vehicular-derived SOA, with substantial contributions from aromatic and aliphatic hydrocarbons. Including these insights on source characterization and SOA formation will improve regional pollution control policies, fuel regulations, and methodologies for future measurement, laboratory, and modeling studies.
While a third of the world carries the burden of tuberculosis, disease control has been hindered by a lack of tools, including a rapid, point-of-care diagnostic and a protective vaccine. In many ...infectious diseases, antibodies (Abs) are powerful biomarkers and important immune mediators. However, in Mycobacterium tuberculosis (Mtb) infection, a discriminatory or protective role for humoral immunity remains unclear. Using an unbiased antibody profiling approach, we show that individuals with latent tuberculosis infection (Ltb) and active tuberculosis disease (Atb) have distinct Mtb-specific humoral responses, such that Ltb infection is associated with unique Ab Fc functional profiles, selective binding to FcγRIII, and distinct Ab glycosylation patterns. Moreover, compared to Abs from Atb, Abs from Ltb drove enhanced phagolysosomal maturation, inflammasome activation, and, most importantly, macrophage killing of intracellular Mtb. Combined, these data point to a potential role for Fc-mediated Ab effector functions, tuned via differential glycosylation, in Mtb control.
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•Individuals with latent and active TB infection have divergent humoral signatures•Antibodies in latent TB infection have enhanced Fc effector profiles•Antibody glycosylation patterns can discriminate between latent and active TB•Antibodies in latent TB infection drive macrophages to kill intracellular bacteria
Individuals with active and latent tuberculosis (TB) infections can be distinguished by the type of antibodies they produce, pointing toward an important and unappreciated contribution from humoral immunity in controlling chronic TB.
The chemical complexity of atmospheric organic aerosol (OA) has caused substantial uncertainties in understanding its origins and environmental impacts. Here, we provide constraints on OA origins ...through compositional characterization with molecular-level details. Our results suggest that secondary OA (SOA) from monoterpene oxidation accounts for approximately half of summertime fine OA in Centreville, AL, a forested area in the southeastern United States influenced by anthropogenic pollution. We find that different chemical processes involving nitrogen oxides, during days and nights, play a central role in determining the mass of monoterpene SOA produced. These findings elucidate the strong anthropogenic–biogenic interaction affecting ambient aerosol in the southeastern United States and point out the importance of reducing anthropogenic emissions, especially under a changing climate, where biogenic emissions will likely keep increasing.
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