A novel fast gas chromatography method for higher time resolution measurements of speciated monoterpenes in air

Biogenic emissions supply the largest fraction of non-methane volatile organic compounds (VOC) from the biosphere to the atmospheric boundary layer, and typically comprise a complex mixture of reactive terpenes. Due to this chemical complexity, achieving comprehensive measurements of biogenic VOC (BVOC) in air within a satisfactory time resolution is analytically challenging. To address this, we have developed a novel, fully automated Fast Gas Chromatography (Fast-GC) based technique to provide higher time resolution monitoring of monoterpenes (and selected other C₉-C₁₅ terpenes) during plant emission studies and in ambient air. To our knowledge, this is the first study to apply a Fast-GC based separation technique to achieve quantification of terpenes in ambient air. Three chromatography methods have been developed for atmospheric terpene analysis under different sampling scenarios. Each method facilitates chromatographic separation of selected BVOC within a significantly reduced analysis time compared to conventional GC methods, whilst maintaining the ability to quantify individual monoterpene structural isomers. Using this approach, the C₉-C₁₅ BVOC composition of single plant emissions may be characterised within a 14.5 min analysis time. Moreover, in-situ quantification of 12 monoterpenes in unpolluted ambient air may be achieved within an 11.7 min chromatographic separation time (increasing to 19.7 min when simultaneous quantification of multiple oxygenated C₉-C₁₀ terpenoids is required, and/or when concentrations of anthropogenic VOC are significant). These analysis times potentially allow for a twofold to fivefold increase in measurement frequency compared to conventional GC methods. Here we outline the technical details and analytical capability of this chromatographic approach, and present the first in-situ Fast-GC observations of 6 monoterpenes and the oxygenated BVOC (OBVOC) linalool in ambient air. During this field deployment within a suburban forest ~30 km west of central Tokyo, Japan, the Fast-GC limit of detection with respect to monoterpenes was 4–5 ppt, and the agreement between Fast-GC and PTR-MS derived total monoterpene mixing ratios was consistent with previous GC/PTR-MS comparisons. The measurement uncertainties associated with the Fast-GC quantification of monoterpenes are ≤ 12%, while larger uncertainties (up to ~25%) are associated with the OBVOC and sesquiterpene measurements

Sensitivity analyses of OH missing sinks over Tokyo metropolitan area in the summer of 2007

OH reactivity is one of key indicators which reflect impacts of photochemical reactions in the atmosphere. An observation campaign has been conducted in the summer of 2007 at the heart of Tokyo metropolitan area to measure OH reactivity. The total OH reactivity measured directly by the laser-induced pump and probe technique was higher than the sum of the OH reactivity calculated from concentrations and reaction rate coefficients of individual species measured in this campaign. And then, three-dimensional air quality simulation has been conducted to evaluate the simulation performance on the total OH reactivity including "missing sinks", which correspond to the difference between the measured and calculated total OH reactivity. The simulated OH reactivity is significantly underestimated because the OH reactivity of volatile organic compounds (VOCs) and missing sinks are underestimated. When scaling factors are applied to input emissions and boundary concentrations, a good agreement is observed between the simulated and measured concentrations of VOCs. However, the simulated OH reactivity of missing sinks is still underestimated. Therefore, impacts of unidentified missing sinks are investigated through sensitivity analyses. In the cases that unknown secondary products are assumed to account for unidentified missing sinks, they tend to suppress formation of secondary aerosol components and enhance formation of ozone. In the cases that unidentified primary emitted species are assumed to account for unidentified missing sinks, a variety of impacts may be observed, which could serve as precursors of secondary organic aerosols (SOA) and significantly increase SOA formation. Missing sinks are considered to play an important role in the atmosphere over Tokyo metropolitan area

Isoprene oxidation products are a significant atmospheric aerosol component

International audienceGlycolaldehyde, hydroxyacetone, and methylglyoxal, which are known isoprene oxidation products, were collected during two field experiments using an annular denuder sampling system and compared to a model calculation. The compounds in gas and aerosol phases were determined during both experiments. Global variation and distribution of the aerosol mass contribution of the compounds were predicted using the measurements, the box model results, and gas-phase concentrations and humidity simulated by a global 3-D model. Here we report the estimates of a global annual contribution of 35 (10?120) Tg of aerosol organic matter from isoprene

Seasonal variation of carbon monoxide in northern Japan: Fourier transform IR measurements and source-labeled model calculations

Tropospheric carbon monoxide (CO) was measured throughout 2001 using groundbased Fourier transform IR (FTIR) spectrometers at Moshiri 44.4N and Rikubetsu 43.5N) observatories in northern Japan, which are separated by 150 km. Seasonal and day-to-day variations of CO are studied using these data, and contributions from various CO sources are evaluated using three-dimensional global chemistry transport model (GEOS-CHEM) calculations. Seasonal maximum and minimum FTIR-derived tropospheric CO amounts occurred in April and September, respectively. The ratio of partial column amounts between the 0–4 and 0–12 km altitude ranges is found to be slightly greater in early spring. The GEOS-CHEM model calculations generally reproduce these observed features. Source-labeled CO model calculations suggest that the observed seasonal variation is caused by seasonal contributions from various sources, in addition to a seasonal change in chemical CO loss by OH. Changes in meteorological fields largely control the relative importance of various source contributions. The contributions from fossil fuel (FF) combustion in Asia and photochemical CO production have the greatest yearly averaged contribution at 1 km among the CO sources (31% each). The Asian FF contribution increases from winter to summer, because weak southwesterly wind in summer brings more Asian pollutants to the observation sites. The seasonal variation from photochemical CO production is small (±17% at 1 km), likely because of concurrent increases (decreases) of photochemical production and loss rates in summer (winter), with the largest contribution between August and December. The contribution from intercontinental transport of European FF combustion CO is found to be comparable to that of Asian FF sources in winter. Northwesterly wind around the Siberian high in this season brings pollutants from Europe directly to Japan, in addition to southward transport of accumulated pollution from higher latitudes. The influences are generally greater at lower altitudes, resulting in a vertical gradient in the CO profile during winter. The model underestimates total CO by 12–14% between March and June. Satellite-derived fire-count data and the relationship between FTIR-derived HCN and CO amounts are generally consistent with biomass burning influences, which could have been underestimated by the model calculations

Technical Note: Formal blind intercomparison of HO₂ measurements in the atmosphere simulation chamber SAPHIR during the HOxComp campaign

Hydroperoxy radical (HO₂) concentrations were measured during the formal blind intercomparison campaign HOxComp carried out in Jülich, Germany, in 2005. Three instruments detected HO₂ via chemical conversion to hydroxyl radicals (OH) and subsequent detection of the sum of OH and HO₂ by laser induced fluorescence (LIF). All instruments were based on the same detection and calibration scheme. Because measurements by a MIESR instrument failed during the campaign, no absolute reference measurement was available, so that the accuracy of individual instruments could not be addressed. Instruments sampled ambient air for three days and were attached to the atmosphere simulation chamber SAPHIR during the second part of the campaign. Six experiments of one day each were conducted in SAPHIR, where air masses are homogeneously mixed, in order to investigate the performance of instruments and to determine potential interferences of measurements under well-controlled conditions. Linear correlation coefficients (<i>R</i>²) between measurements of the LIF instruments are generally high and range from 0.82 to 0.98. However, the agreement between measurements is variable. The regression analysis of the entire data set of measurements in SAPHIR yields slopes between 0.69 to 1.26 and intercepts are smaller than typical atmospheric daytime concentrations (less than 1 pptv). The quality of fit parameters improves significantly, when data are grouped into data subsets of similar water vapor concentrations. Because measurements of LIF instruments were corrected for a well-characterized water dependence of their sensitivities, this indicates that an unknown factor related to water vapor affected measurements in SAPHIR. Measurements in ambient air are also well-correlated, but regression parameters differ from results obtained from SAPHIR experiments. This could have been caused by differences in HO₂ concentrations in the sampled air at the slightly different locations of instruments

First direct measurements of formaldehyde flux via eddy covariance: implications for missing in-canopy formaldehyde sources

We report the first observations of formaldehyde (HCHO) flux measured via eddy covariance, as well as HCHO concentrations and gradients, as observed by the Madison Fiber Laser-Induced Fluorescence Instrument during the BEACHON-ROCS 2010 campaign in a rural, Ponderosa Pine forest northwest of Colorado Springs, CO. A median noon upward flux of ~80 &amp;mu;g m&lt;sup&gt;&amp;minus;2&lt;/sup&gt; h&lt;sup&gt;&amp;minus;1&lt;/sup&gt; (~24 ppt&lt;sub&gt;v&lt;/sub&gt; m s&lt;sup&gt;&amp;minus;1&lt;/sup&gt;) was observed with a noon range of 37 to 131 &amp;mu;g m&lt;sup&gt;&amp;minus;2&lt;/sup&gt; h&lt;sup&gt;&amp;minus;1&lt;/sup&gt;. Enclosure experiments were performed to determine the HCHO branch (3.5 &amp;mu;g m&lt;sup&gt;-2&lt;/sup&gt; h&lt;sup&gt;&amp;minus;1&lt;/sup&gt;) and soil (7.3 &amp;mu;g m&lt;sup&gt;&amp;minus;2&lt;/sup&gt; h&lt;sup&gt;&amp;minus;1&lt;/sup&gt;) direct emission rates in the canopy. A zero-dimensional canopy box model, used to determine the apportionment of HCHO source and sink contributions to the flux, underpredicted the observed HCHO flux by a factor of 6. Simulated increases in concentrations of species similar to monoterpenes resulted in poor agreement with measurements, while simulated increases in direct HCHO emissions and/or concentrations of species similar to 2-methyl-3-buten-2-ol best improved model/measurement agreement. Given the typical diurnal variability of these BVOC emissions and direct HCHO emissions, this suggests that the source of the missing flux is a process with both a strong temperature and radiation dependence

Placental syncytiotrophoblast constitutes a major barrier to vertical transmission of Listeria monocytogenes.

Listeria monocytogenes is an important cause of maternal-fetal infections and serves as a model organism to study these important but poorly understood events. L. monocytogenes can infect non-phagocytic cells by two means: direct invasion and cell-to-cell spread. The relative contribution of each method to placental infection is controversial, as is the anatomical site of invasion. Here, we report for the first time the use of first trimester placental organ cultures to quantitatively analyze L. monocytogenes infection of the human placenta. Contrary to previous reports, we found that the syncytiotrophoblast, which constitutes most of the placental surface and is bathed in maternal blood, was highly resistant to L. monocytogenes infection by either internalin-mediated invasion or cell-to-cell spread. Instead, extravillous cytotrophoblasts-which anchor the placenta in the decidua (uterine lining) and abundantly express E-cadherin-served as the primary portal of entry for L. monocytogenes from both extracellular and intracellular compartments. Subsequent bacterial dissemination to the villous stroma, where fetal capillaries are found, was hampered by further cellular and histological barriers. Our study suggests the placenta has evolved multiple mechanisms to resist pathogen infection, especially from maternal blood. These findings provide a novel explanation why almost all placental pathogens have intracellular life cycles: they may need maternal cells to reach the decidua and infect the placenta

Missing peroxy radical sources within a summertime ponderosa pine forest

Organic peroxy (RO₂) and hydroperoxy (HO₂) radicals are key intermediates in the photochemical processes that generate ozone, secondary organic aerosol and reactive nitrogen reservoirs throughout the troposphere. In regions with ample biogenic hydrocarbons, the richness and complexity of peroxy radical chemistry presents a significant challenge to current-generation models, especially given the scarcity of measurements in such environments. We present peroxy radical observations acquired within a ponderosa pine forest during the summer 2010 Bio-hydro-atmosphere interactions of Energy, Aerosols, Carbon, H₂O, Organics and Nitrogen – Rocky Mountain Organic Carbon Study (BEACHON-ROCS). Total peroxy radical mixing ratios reach as high as 180 pptv (parts per trillion by volume) and are among the highest yet recorded. Using the comprehensive measurement suite to constrain a near-explicit 0-D box model, we investigate the sources, sinks and distribution of peroxy radicals below the forest canopy. The base chemical mechanism underestimates total peroxy radicals by as much as a factor of 3. Since primary reaction partners for peroxy radicals are either measured (NO) or underpredicted (HO₂ and RO₂, i.e., self-reaction), missing sources are the most likely explanation for this result. A close comparison of model output with observations reveals at least two distinct source signatures. The first missing source, characterized by a sharp midday maximum and a strong dependence on solar radiation, is consistent with photolytic production of HO₂. The diel profile of the second missing source peaks in the afternoon and suggests a process that generates RO₂ independently of sun-driven photochemistry, such as ozonolysis of reactive hydrocarbons. The maximum magnitudes of these missing sources (~120 and 50 pptv min⁻¹, respectively) are consistent with previous observations alluding to unexpectedly intense oxidation within forests. We conclude that a similar mechanism may underlie many such observations