Chemical ionization tandem mass spectrometer for the in situ measurement of methyl hydrogen peroxide

A new approach for measuring gas-phase methyl hydrogen peroxide [(MHP) CH_3OOH] utilizing chemical ionization mass spectrometry is presented. Tandem mass spectrometry is used to avoid mass interferences that hindered previous attempts to measure atmospheric CH_3OOH with CF_3O− clustering chemistry. CH_3OOH has been successfully measured in situ using this technique during both airborne and ground-based campaigns. The accuracy and precision for the MHP measurement are a function of water vapor mixing ratio. Typical precision at 500 pptv MHP and 100 ppmv H_2O is ±80 pptv (2 sigma) for a 1 s integration period. The accuracy at 100 ppmv H_2O is estimated to be better than ±40%. Chemical ionization tandem mass spectrometry shows considerable promise for the determination of in situ atmospheric trace gas mixing ratios where isobaric compounds or mass interferences impede accurate measurements

Paraoxonase gene polymorphisms and haplotype analysis in a stroke population

Peer reviewedPublisher PD

Age-related decrements in cycling and running performance

Objective. This study examined age-related decrements in athletic performance during running and cycling activities. Design. The age group winning times for males aged between 18 and 70 years competing in the 1999 Argus cycle tour (103 km) and 1999 Comrades running marathon (90 km), South Africa's premier endurance cycling and running events respectively, were examined. Main outcome measures. The relationship between speed (cycling and running respectively) and age was calculated using a 4th order polynomial function. The derivative of each of these functions was determined and then the slope of the function corresponding to each age was calculated. Results. The rate of decline in running speed occurred at an earlier age (~ 32 years) during the running race compared with the cycling tour (~ 55 years). Conclusions. These findings establish a trend that there is ‘accelerated' aging during running which can perhaps be attributed to the increased weight-bearing stress on the muscles during running compared with cycling

Agricultural fires in the southeastern U.S. during SEAC^4RS: Emissions of trace gases and particles and evolution of ozone, reactive nitrogen, and organic aerosol

Emissions from 15 agricultural fires in the southeastern U.S. were measured from the NASA DC-8 research aircraft during the summer 2013 Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC^4RS) campaign. This study reports a detailed set of emission factors (EFs) for 25 trace gases and 6 fine particle species. The chemical evolution of the primary emissions in seven plumes was examined in detail for ~1.2 h. A Lagrangian plume cross-section model was used to simulate the evolution of ozone (O_3), reactive nitrogen species, and organic aerosol (OA). Observed EFs are generally consistent with previous measurements of crop residue burning, but the fires studied here emitted high amounts of SO_2 and fine particles, especially primary OA and chloride. Filter-based measurements of aerosol light absorption implied that brown carbon (BrC) was ubiquitous in the plumes. In aged plumes, rapid production of O_3, peroxyacetyl nitrate (PAN), and nitrate was observed with ΔO_3/ΔCO, ΔPAN/ΔNO_y, and Δnitrate/ΔNO_y reaching ~0.1, ~0.3, and ~0.3. For five selected cases, the model reasonably simulated O_3 formation but underestimated PAN formation. No significant evolution of OA mass or BrC absorption was observed. However, a consistent increase in oxygen-to-carbon (O/C) ratios of OA indicated that OA oxidation in the agricultural fire plumes was much faster than in urban and forest fire plumes. Finally, total annual SO_2, NO_x, and CO emissions from agricultural fires in Arkansas, Louisiana, Mississippi, and Missouri were estimated (within a factor of ~2) to be equivalent to ~2% SO_2 from coal combustion and ~1% NO_x and ~9% CO from mobile sources

Airborne measurements of western U.S. wildfire emissions: Comparison with prescribed burning and air quality implications

Wildfires emit significant amounts of pollutants that degrade air quality. Plumes from three wildfires in the western U.S. were measured from aircraft during the Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC^4RS) and the Biomass Burning Observation Project (BBOP), both in summer 2013. This study reports an extensive set of emission factors (EFs) for over 80 gases and 5 components of submicron particulate matter (PM_1) from these temperate wildfires. These include rarely, or never before, measured oxygenated volatile organic compounds and multifunctional organic nitrates. The observed EFs are compared with previous measurements of temperate wildfires, boreal forest fires, and temperate prescribed fires. The wildfires emitted high amounts of PM_1 (with organic aerosol (OA) dominating the mass) with an average EF that is more than 2 times the EFs for prescribed fires. The measured EFs were used to estimate the annual wildfire emissions of carbon monoxide, nitrogen oxides, total nonmethane organic compounds, and PM_1 from 11 western U.S. states. The estimated gas emissions are generally comparable with the 2011 National Emissions Inventory (NEI). However, our PM_1 emission estimate (1530 ± 570 Gg yr^(−1)) is over 3 times that of the NEI PM_(2.5) estimate and is also higher than the PM_(2.5) emitted from all other sources in these states in the NEI. This study indicates that the source of OA from biomass burning in the western states is significantly underestimated. In addition, our results indicate that prescribed burning may be an effective method to reduce fine particle emissions

Urban agriculture : evaluating informal and formal practices

Urban agriculture (UA) is a fast-increasing element in many settlements in the Global North. This paper reviews the diversity of UA activity, ranging from legal to illegal, formal to informal. Focusing particularly on current research on UA projects in England, including small-scale guerrilla gardening and large community projects supported by community and government funding, we look at the realities of UA. We suggest that it is under-theorised as previous research has focused on practicalities and activism. In particular, we highlight the problematic contribution of UA to food production, the wider value in terms of community development, health and wellbeing, and warn of the danger of the ‘local trap’

Quantification of hydroxyacetone and glycolaldehyde using chemical ionization mass spectrometry

Chemical ionization mass spectrometry (CIMS) enables online, rapid, in situ detection and quantification of hydroxyacetone and glycolaldehyde. Two different CIMS approaches are demonstrated employing the strengths of single quadrupole mass spectrometry and triple quadrupole (tandem) mass spectrometry. Both methods are generally capable of the measurement of hydroxyacetone, an analyte with known but minimal isobaric interferences. Tandem mass spectrometry provides direct separation of the isobaric compounds glycolaldehyde and acetic acid using distinct, collision-induced dissociation daughter ions. The single quadrupole CIMS measurement of glycolaldehyde was demonstrated during the ARCTAS-CARB (Arctic Research of the Composition of the Troposphere from Aircraft and Satellites - California Air Resources Board) 2008 campaign, while triple quadrupole CIMS measurements of glycolaldehyde and hydroxyacetone were demonstrated during the BEARPEX (Biosphere Effects on Aerosols and Photochemistry Experiment) 2009 campaign. Enhancement ratios of glycolaldehyde in ambient biomass-burning plumes are reported for the ARCTAS-CARB campaign. BEARPEX observations are compared to simple photochemical box model predictions of biogenic volatile organic compound oxidation at the site

Sources, seasonality, and trends of southeast US aerosol: an integrated analysis of surface, aircraft, and satellite observations with the GEOS-Chem chemical transport model

We use an ensemble of surface (EPA CSN, IMPROVE, SEARCH, AERONET), aircraft (SEAC4RS), and satellite (MODIS, MISR) observations over the southeast US during the summer–fall of 2013 to better understand aerosol sources in the region and the relationship between surface particulate matter (PM) and aerosol optical depth (AOD). The GEOS-Chem global chemical transport model (CTM) with 25 × 25 km^2 resolution over North America is used as a common platform to interpret measurements of different aerosol variables made at different times and locations. Sulfate and organic aerosol (OA) are the main contributors to surface PM_(2.5) (mass concentration of PM finer than 2.5 μm aerodynamic diameter) and AOD over the southeast US. OA is simulated successfully with a simple parameterization, assuming irreversible uptake of low-volatility products of hydrocarbon oxidation. Biogenic isoprene and monoterpenes account for 60 % of OA, anthropogenic sources for 30 %, and open fires for 10 %. 60 % of total aerosol mass is in the mixed layer below 1.5 km, 25 % in the cloud convective layer at 1.5–3 km, and 15 % in the free troposphere above 3 km. This vertical profile is well captured by GEOS-Chem, arguing against a high-altitude source of OA. The extent of sulfate neutralization (f = [NH_4^+]/(2[SO_4^(2−)] + [NO_3^−]) is only 0.5–0.7 mol mol^(−1) in the observations, despite an excess of ammonia present, which could reflect suppression of ammonia uptake by OA. This would explain the long-term decline of ammonium aerosol in the southeast US, paralleling that of sulfate. The vertical profile of aerosol extinction over the southeast US follows closely that of aerosol mass. GEOS-Chem reproduces observed total column aerosol mass over the southeast US within 6 %, column aerosol extinction within 16 %, and space-based AOD within 8–28 % (consistently biased low). The large AOD decline observed from summer to winter is driven by sharp declines in both sulfate and OA from August to October. These declines are due to shutdowns in both biogenic emissions and UV-driven photochemistry. Surface PM_(2.5) shows far less summer-to-winter decrease than AOD and we attribute this in part to the offsetting effect of weaker boundary layer ventilation. The SEAC4RS aircraft data demonstrate that AODs measured from space are consistent with surface PM_(2.5). This implies that satellites can be used reliably to infer surface PM_(2.5) over monthly timescales if a good CTM representation of the aerosol vertical profile is available

Electrically conductive polyimides containing silver trifluoroacetylacetonate

Polyimides with enhanced electrical conductivity are produced by adding a silver ion-containing additive to the polyamic acid resin formed by the condensation of an aromatic dianhydride with an aromatic diamine. After thermal treatment the resulting polyimides had surface conductivities in the range of 1.7.times.10.sup.-3 4.5 .OMEGA..sup.-1 making them useful in low the electronics industry as flexible, electrically conductive polymeric films and coatings