Atmospheric free radicals are low concentration, relatively fast reacting species whose influence is felt throughout the atmosphere. Reactive radicals have a key role in maintaining a balanced ...atmospheric composition through their central function in controlling the oxidative capacity of the atmosphere. In this tutorial review, the chemistry of three main groups of atmospheric radicals HO(x), NO(x) and XO(x)(X = Cl, Br, I) are examined in terms of their sources, interconversions and sinks. Key examples of the chemistry are given for each group of radicals in their atmospheric context.
Is wind direction an adequate marker of air mass history? This review looks at the evolution of methods for assessing the effect of the origin and pathway of air masses on composition change and ...trends. The composition of air masses and how they evolve and the changing contribution of sources and receptors are key elements in atmospheric science. Source–receptor relationships of atmospheric composition can be investigated with back trajectory techniques, tracing forward from a defined geographical origin to arrive at measurement sites where the composition may have altered during transport.
The distinction between the use of wind sector analysis, trajectory models and dispersion models to interpret composition measurements is explained and the advantages and disadvantages of each are illustrated with examples. Historical uses of wind roses, back trajectories and dispersion models are explained as well as the methods for grouping and clustering air masses. The interface of these methods to the corresponding chemistry measured at the receptor sites is explored. The review does not detail the meteorological derivation of trajectories or the complexity of the models but focus on their application and the statistical analyses used to compare them with in situ composition measurements. A newly developed methodology for analysing atmospheric observatory composition data according to air mass pathways calculated with the NAME dispersion model is given as a detailed case study. The steps in this methodology are explained with relevance to the Weybourne Atmospheric Observatory in the UK.
► Understanding air mass origin is essential to interpreting composition measurements. ► The use of wind measurements, trajectories and dispersion models are explained. ► Methods to link meteorological measurements with composition are explored. ► An historical and practical perspective on the various methods is given. ► A case study using the NAME dispersion model illustrates one such method.
A mass spectrometry technique developed to examine gaseous organic compounds is discussed. Also explored is the history, thermodynamics and kinetics of proton transfer reactions, upon which this ...technique depends.
Speciated volatile organic compound (VOC) and carbon monoxide (CO) measurements from the Marylebone Road site in central London from 1998 through 2008 are presented. Long-term trends show ...statistically significant decreases for all the VOCs considered, ranging from −3% to −26% per year. Carbon monoxide decreased by −12% per year over the measurement period. The VOC trends observed at the kerbside site in London showed greater rates of decline relative to trends from monitoring sites in rural England (Harwell) and a remote high-altitude site (Hohenpeissenberg), which showed decreases for individual VOCs from −2% to −13% per year. Over the same 1998 through 2008 period VOC to CO ratios for London remained steady, an indication that emissions reduction measures affected the measured compounds equally. Relative trends comparing VOC to CO ratios between Marylebone Road and Hohenpeissenberg showed greater similarities than absolute trends, indicating that emissions reductions measures in urban areas are reflected by regional background locations. A comparison of VOC mixing ratios and VOC to CO ratios was undertaken for London and other global cities. Carbon monoxide and VOCs (alkanes greater than C
5, alkenes, and aromatics) were found to be strongly correlated (>0.8) in the Annex I countries, whereas only ethene and ethyne were strongly correlated with CO in the non-Annex I countries. The correlation results indicate significant emissions from traffic-related sources in Annex I countries, and a much larger influence of other sources, such as industry and LPG-related sources in non-Annex I countries. Yearly benzene to ethyne ratios for London from 2000 to 2008 ranged from 0.17 to 0.29 and compared well with previous results from US cities and three global megacities.
Long‐term atmospheric NOx/CO enhancement ratios in megacities provide evaluations of emission inventories. A fuel‐based emission inventory approach that diverges from conventional bottom‐up inventory ...methods explains 1970–2015 trends in NOx/CO enhancement ratios in Los Angeles. Combining this comparison with similar measurements in other U.S. cities demonstrates that motor vehicle emissions controls were largely responsible for U.S. urban NOx/CO trends in the past half century. Differing NOx/CO enhancement ratio trends in U.S. and European cities over the past 25 years highlights alternative strategies for mitigating transportation emissions, reflecting Europe's increased use of light‐duty diesel vehicles and correspondingly slower decreases in NOx emissions compared to the U.S. A global inventory widely used by global chemistry models fails to capture these long‐term trends and regional differences in U.S. and Europe megacity NOx/CO enhancement ratios, possibly contributing to these models' inability to accurately reproduce observed long‐term changes in tropospheric ozone.
Key Points
Measured NOx/CO enhancement ratio trends are compared to inventory emissions ratio trends in megacities
Chemistry‐climate modeling inventory fails to capture NOx/CO emission ratio trends and regional differences
Observations demonstrate divergent paths in motor vehicle emission control strategies in the U.S. versus Europe
The folate-driven one-carbon (1C) cycle is a fundamental metabolic hub in cells that enables the synthesis of nucleotides and amino acids and epigenetic modifications. This cycle might also release ...formaldehyde, a potent protein and DNA crosslinking agent that organisms produce in substantial quantities. Here we show that supplementation with tetrahydrofolate, the essential cofactor of this cycle, and other oxidation-prone folate derivatives kills human, mouse and chicken cells that cannot detoxify formaldehyde or that lack DNA crosslink repair. Notably, formaldehyde is generated from oxidative decomposition of the folate backbone. Furthermore, we find that formaldehyde detoxification in human cells generates formate, and thereby promotes nucleotide synthesis. This supply of 1C units is sufficient to sustain the growth of cells that are unable to use serine, which is the predominant source of 1C units. These findings identify an unexpected source of formaldehyde and, more generally, indicate that the detoxification of this ubiquitous endogenous genotoxin creates a benign 1C unit that can sustain essential metabolism.
Abstract
Formaldehyde (HCHO) is a toxic and carcinogenic pollutant and human metabolite that reacts with biomolecules under physiological conditions. Quantifying HCHO is essential for ongoing ...biological and biomedical research on HCHO; however, its reactivity, small size and volatility make this challenging. Here, we report a novel HCHO detection/quantification method that couples cysteamine-mediated HCHO scavenging with SPME GC–MS analysis. Our NMR studies confirm cysteamine as an efficient and selective HCHO scavenger that out-competes O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine, the most commonly used scavenger, and forms a stable thiazolidine amenable to GC–MS quantification. Validation of our GC–MS method using FDA and EMA guidelines revealed detection and quantification limits in the nanomolar and micromolar ranges respectively, while analysis of bacterial cell lysate confirmed its applicability in biological samples. Overall, our studies confirm that cysteamine scavenging coupled to SPME GC–MS analysis provides a sensitive and chemically robust method to quantify HCHO in biological samples.
Land use regression (LUR) models have been used in epidemiology to determine the fine-scale spatial variation in air pollutants such as nitrogen dioxide (NO2) in cities and larger regions. However, ...they are often limited in their temporal resolution, which may potentially be rectified by employing the synoptic coverage provided by satellite measurements. In this work a mixed-effects LUR model is developed to model daily surface NO2 concentrations over the Hong Kong SAR during the period 2005–2015. In situ measurements from the Hong Kong Air Quality Monitoring Network, along with tropospheric vertical column density (VCD) data from the OMI, GOME-2A, and SCIAMACHY satellite instruments were combined with fine-scale land use parameters to provide the spatiotemporal information necessary to predict daily surface concentrations. Cross-validation with the in situ data shows that the mixed-effects LUR model using OMI data has a high predictive power (adj. R2 = 0. 84), especially when compared with surface concentrations derived using the MACC-II reanalysis model dataset (adj. R2 = 0. 11). Time series analysis shows no statistically significant trend in NO2 concentrations during 2005–2015, despite a reported decline in NOx emissions. This study demonstrates the utility in combining satellite data with LUR models to derive daily maps of ambient surface NO2 for use in exposure studies.
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