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Journal Articles
Elementa: Science of the Anthropocene (2020) 8: 46.
Published: 25 August 2020
Abstract
To understand the characteristics of air quality in the Seoul Metropolitan Area, intensive measurements were conducted under the Korea-United States Air Quality (KORUS-AQ) campaign. Trace gases such as O 3 , NO x , NO y , SO 2 , CO, and volatile organic compounds (VOCs), photochemical byproducts such as H 2 O 2 and HCHO, aerosol species, and meteorological variables including planetary boundary layer height were simultaneously measured at Olympic Park in Seoul. During the measurement period, high O 3 episodes that exceeded the 90 ppbv hourly maximum occurred on 14 days under four distinct synoptic meteorological conditions. Furthermore, local circulation such as land–sea breeze and diurnal evolution of the boundary layer were crucial in determining the concentrations of precursor gases, including NO x and VOC as well as O 3 . During such episodes, the nighttime NO x and VOC and daytime UV levels were higher compared to non-episode days. The overall precursor levels and photochemical activity were represented fairly well by variations in the HCHO, which peaked in the morning during the high O 3 episodes. This study revealed that toluene was the most abundant VOC in Seoul, and its concentration increased greatly with NO x due to the large local influence under stagnant conditions. When O 3 was highly elevated concurrently with PM 2.5 under dominant westerlies, NO x and VOCs were relatively lower and CO was noticeably higher than in other episodes. Additionally, the O 3 production efficiency was the highest due to a low NO x with the highest NO z /NO y ratio among the four episodes. When westerlies were dominant in transport-south episode, the nighttime concentration of O 3 remained as high as 40~50 ppbv due to the minimum level of NO x titration. Overall, the Seoul Metropolitan Area is at NO x -saturated and VOC-limited conditions, which was diagnosed by indicator species and VOC/NO x ratios.
Includes: Supplementary data
Journal Articles
Elementa: Science of the Anthropocene (2020) 8: 45.
Published: 24 August 2020
Abstract
Many ecosystems are experiencing an increase in drought conditions as a consequence of climate warming and changing precipitation patterns. The stress imposed by these environmental changes can affect ecosystem processes such as the extracellular enzymatic degradation of carbon-containing leaf litter by soil microbial communities. However, the magnitude of these impacts may depend on the composition and metabolism of the microbial community. Based on the hypothesis of local adaptation, microbial communities native to warm-dry ecosystems should display a greater capacity to degrade leaf litter polymers with extracellular enzymes following exposure to warm-dry conditions. To test this hypothesis, we performed a microcosm study in which we monitored extracellular enzyme activity and respiration of microbial communities from five ecosystems along a southern California climate gradient, ranging from warmer, drier desert to wetter, cooler subalpine forest. To simulate drought and rewetting, we subjected microcosms to periods of high temperature and low moisture followed by a water pulse. We found that enzyme activity of wet-cool communities generally exceeded that of warm-dry communities across enzyme types for the five sites we considered. Additionally, we observed a significant decrease in respiration for all communities after longer durations of drought exposure. Although these findings did not align with our expectations of local adaptation, they suggest litter-inhabiting microbial communities are able to retain metabolic functioning in environmental conditions different from those of their native ecosystems. These results may imply that factors such as litter chemistry impose greater constraints than climate on community metabolic function. Overall, despite differences in local climates, microbial communities from semiarid regions may be metabolically adapted to maintain functioning in the face of drought.
Includes: Supplementary data
Journal Articles
Elementa: Science of the Anthropocene (2020) 8: 44.
Published: 20 August 2020
Abstract
Mercury (Hg) contamination is an environmental concern as a by-product of legacy mining in Australia. Here we investigate the spatial and temporal distribution of Hg in the Molonglo River system in New South Wales, Australia, and assess the physical and chemical factors influencing that distribution. Mercury concentrations in sediment cores were measured in conjunction with 210 Pb and 137 Cs dating to establish historical contamination. This was done at the source mine site of Captains Flat, New South Wales, and the system’s sink in Lake Burley Griffin, Australian Capital Territory. Additionally, surficial sediment Hg concentrations along the Molonglo River were analyzed to determine the spatial distribution of Hg. Analytical results showed the primary physical and chemical factors influencing Hg dispersion to be distance, total organic matter, and the presence of iron oxides and oxyhydroxides. The highest Hg concentrations were near the mine site at Captains Flat and decreased significantly with distance. Sediment core analyses in both Captains Flat and the lake showed reductions in Hg concentrations toward surficial sediment layers. It is suggested government-funded rehabilitation programs are playing a part in reducing the release of metal contamination.
Includes: Supplementary data
Journal Articles
Elementa: Science of the Anthropocene (2020) 8: 37.
Published: 11 August 2020
Abstract
The Korea-United States Air Quality Study (KORUS-AQ) took place in spring 2016 to better understand air pollution in Korea. In support of KORUS-AQ, 2554 whole air samples (WAS) were collected aboard the NASA DC-8 research aircraft and analyzed for 82 C 1 –C 10 volatile organic compounds (VOCs) using multi-column gas chromatography. Together with fast-response measurements from other groups, the air samples were used to characterize the VOC composition in Seoul and surrounding regions, determine which VOCs are major ozone precursors in Seoul, and identify the sources of these reactive VOCs. (1) The WAS VOCs showed distinct signatures depending on their source origins. Air collected over Seoul had abundant ethane, propane, toluene and n -butane while plumes from the Daesan petrochemical complex were rich in ethene, C 2 –C 6 alkanes and benzene. Carbonyl sulfide (COS), CFC-113, CFC-114, carbon tetrachloride (CCl 4 ) and 1,2-dichloroethane were good tracers of air originating from China. CFC-11 was also elevated in air from China but was surprisingly more elevated in air over Seoul. (2) Methanol, isoprene, toluene, xylenes and ethene were strong individual contributors to OH reactivity in Seoul. However methanol contributed less to ozone formation based on photochemical box modeling, which better accounts for radical chemistry. (3) Positive Matrix Factorization (PMF) and other techniques indicated a mix of VOC source influences in Seoul, including solvents, traffic, biogenic, and long-range transport. The solvent and traffic sources were roughly equal using PMF, and the solvents source was stronger in the KORUS-AQ emission inventory. Based on PMF, ethene and propene were primarily associated with traffic, and toluene, ethylbenzene and xylenes with solvents, especially non-paint solvents for toluene and paint solvents for ethylbenzene and xylenes. This suggests that VOC control strategies in Seoul could continue to target vehicle exhaust and paint solvents, with additional regulations to limit the VOC content in a variety of non-paint solvents.
Includes: Supplementary data
Journal Articles
Elementa: Science of the Anthropocene (2020) 8: 32.
Published: 13 July 2020
Abstract
Twelve next generation emission measurement (NGEM) technologies completed single-blind testing at the Methane Emissions Technology Evaluation Center in 2018. This is the first series of tests to evaluate a wide variety of NGEM solutions including handheld, mobile, and continuous monitoring methods using comparable, repeatable protocols. Results assess performance of detection, localization and quantification, albeit with limited statistical significance due to a low number of tests. Overall, a higher detection rate is observed for handheld and mobile solutions than for continuous monitoring solutions. Compared to when a single emission source is present, a decline in detection rate is observed across all methods when multiple, steady emission sources are present. Localization by handheld and mobile solutions is more accurate than continuous monitoring solutions. These results support the common perception that detections by continuous monitoring systems will need to be confirmed and pinpointed by a follow-up inspection. Finally, this and other controlled release experiments, have been performed across a limited range of environmental conditions. To develop robust probability of detection curves needed for demonstrating emission reduction potential of leak detection and repair programs, new protocols are needed to evaluate methods across a wide range of metrological conditions and emission scenarios in a cost-effective manner.
Includes: Supplementary data
Journal Articles
Elementa: Science of the Anthropocene (2020) 8: 29.
Published: 03 July 2020
Abstract
Mercury (Hg) sources to estuaries (natural and anthropogenic) as well as Hg concentrations in Australian nearshore marine environment fish are reviewed herein. The question of whether Australian estuaries have a Hg contamination problem is addressed. The Hg concentrations in fish, excluding sharks, tuna, barramundi and some stingrays, in estuaries and near-shore ecosystems with no discernable pollution sources are typically below 0.5 mg/kg wet weight, the level of health concern. There is no relationship of Hg concentration with fish size or age nor any evidence of biomagnification. In locations with historic large discrete Hg input sources (e.g. Derwent Estuary, Tasmania, Princess Royal Harbour WA, Port Phillip Bay Vic, Sydney sewage outfalls NSW), Hg concentrations in some sediment-dwelling fish such as flatheads exceed the health limit of 0.5 mg/kg. In this paper, we also review, within an Australian context, the biogeochemical processes controlling the formation and accumulation of methyl mercury (MeHg). On entering waterways, Hg rapidly partitions to particulate matter and deposits into sediments. The remobilisation of Hg from sediment is dependent on the formation of MeHg by bacteria and ultimately the interplay of S, Fe and Se cycling. Fish species that move and feed in different areas have Hg concentrations that do not reflect the sediment Hg concentrations where they are caught, i.e. there is an uncoupling of diet and potential Hg exposure. Concluding remarks focus on management interventions: source reduction, preventing eutrophication and promoting system biodiversity and biodiverse diets to mediate the accumulation of Hg in marine organisms and limit the intake of Hg by humans when consuming fish.
Includes: Supplementary data
Journal Articles
Elementa: Science of the Anthropocene (2020) 8: 28.
Published: 01 July 2020
Abstract
The Korea – United States Air Quality Study (May – June 2016) deployed instrumented aircraft and ground-based measurements to elucidate causes of poor air quality related to high ozone and aerosol concentrations in South Korea. This work synthesizes data pertaining to aerosols (specifically, particulate matter with aerodynamic diameters <2.5 micrometers, PM 2.5 ) and conditions leading to violations of South Korean air quality standards (24-hr mean PM 2.5 < 35 µg m –3 ). PM 2.5 variability from AirKorea monitors across South Korea is evaluated. Detailed data from the Seoul vicinity are used to interpret factors that contribute to elevated PM 2.5 . The interplay between meteorology and surface aerosols, contrasting synoptic-scale behavior vs. local influences, is presented. Transboundary transport from upwind sources, vertical mixing and containment of aerosols, and local production of secondary aerosols are discussed. Two meteorological periods are probed for drivers of elevated PM 2.5 . Clear, dry conditions, with limited transport (Stagnant period), promoted photochemical production of secondary organic aerosol from locally emitted precursors. Cloudy humid conditions fostered rapid heterogeneous secondary inorganic aerosol production from local and transported emissions (Transport/Haze period), likely driven by a positive feedback mechanism where water uptake by aerosols increased gas-to-particle partitioning that increased water uptake. Further, clouds reduced solar insolation, suppressing mixing, exacerbating PM 2.5 accumulation in a shallow boundary layer. The combination of factors contributing to enhanced PM 2.5 is challenging to model, complicating quantification of contributions to PM 2.5 from local versus upwind precursors and production. We recommend co-locating additional continuous measurements at a few AirKorea sites across South Korea to help resolve this and other outstanding questions: carbon monoxide/carbon dioxide (transboundary transport tracer), boundary layer height (surface PM 2.5 mixing depth), and aerosol composition with aerosol liquid water (meteorologically-dependent secondary production). These data would aid future research to refine emissions targets to further improve South Korean PM 2.5 air quality.
Includes: Supplementary data
Journal Articles
Elementa: Science of the Anthropocene (2020) 8: 27.
Published: 29 June 2020
Abstract
Terrestrial air-surface exchange of mercury (Hg) forms an important component of the global Hg cycle, with drivers varying across spatial and temporal scales. These drivers include substrate properties, atmospheric chemistry, and meteorological factors. Vegetation uptake represents the dominant pathway of atmospheric Hg deposition to terrestrial surfaces. This study investigated the drivers of net ecosystem exchange of gaseous elemental mercury (Hg 0 ) across multiple seasons in order to gain an understanding of the influence of vegetation and other environmental parameters on the Hg 0 air-surface exchange. Measurements were made continuously using a micrometeorological aerodynamic flux gradient method at a low-vegetated background site in south-eastern Australia, over 14 months. Mean Hg fluxes and atmospheric concentrations across the entire study period were 0.002 ng m –2 h –1 (SD ± 14.23 ng m 2 h –1 ) and 0.68 ng m –3 (SD ± 0.22 ng m –3 ), respectively. Variability was observed across seasons, with the highest average rate of emissions occurring in austral summer (December, January, February) (0.69 ng m –2 h –1 ) and the highest rate of deposition observed in autumn (March, April, May) (–0.50 ng m –2 h –1 ). Vegetation uptake dominated Hg flux during the winter and spring when meteorological conditions were cold and light levels were low. This is supported by CO 2 flux data, with a daytime winter mean of 0.80 µmol m –2 h –1 and a spring daytime mean of 1.54 µmol m –2 h –1 . Summer Hg fluxes were dominantly emission due to higher solar radiation and temperature. Climatic conditions at Oakdale allowed plant production to occur year-round, however the hot dry conditions observed in the warmer months increased evasion, allowing this site to be a small net source of Hg 0 to the atmosphere.
Includes: Supplementary data
Journal Articles
Elementa: Science of the Anthropocene (2020) 8: 23.
Published: 08 June 2020
Abstract
Extracting globally representative trend information from lower tropospheric ozone observations is extremely difficult due to the highly variable distribution and interannual variability of ozone, and the ongoing shift of ozone precursor emissions from high latitudes to low latitudes. Here we report surface ozone trends at 27 globally distributed remote locations (20 in the Northern Hemisphere, 7 in the Southern Hemisphere), focusing on continuous time series that extend from the present back to at least 1995. While these sites are only representative of less than 25% of the global surface area, this analysis provides a range of regional long-term ozone trends for the evaluation of global chemistry-climate models. Trends are based on monthly mean ozone anomalies, and all sites have at least 20 years of data, which improves the likelihood that a robust trend value is due to changes in ozone precursor emissions and/or forced climate change rather than naturally occurring climate variability. Since 1995, the Northern Hemisphere sites are nearly evenly split between positive and negative ozone trends, while 5 of 7 Southern Hemisphere sites have positive trends. Positive trends are in the range of 0.5–2 ppbv decade –1 , with ozone increasing at Mauna Loa by roughly 50% since the late 1950s. Two high elevation Alpine sites, discussed by previous assessments, exhibit decreasing ozone trends in contrast to the positive trend observed by IAGOS commercial aircraft in the European lower free-troposphere. The Alpine sites frequently sample polluted European boundary layer air, especially in summer, and can only be representative of lower free tropospheric ozone if the data are carefully filtered to avoid boundary layer air. The highly variable ozone trends at these 27 surface sites are not necessarily indicative of free tropospheric trends, which have been overwhelmingly positive since the mid-1990s, as shown by recent studies of ozonesonde and aircraft observations.
Includes: Supplementary data
Journal Articles
Elementa: Science of the Anthropocene (2020) 8: 18.
Published: 08 May 2020
Abstract
The Eagle Ford Shale in southern Texas remains one of the most productive oil and gas regions in the US. Like the Permian Basin and Bakken Shale, ubiquitous natural gas flaring serves as an uncertain source of trace gas emissions within the Eagle Ford. A lack of ambient air quality data, especially in the western shale, impedes a thorough understanding of trace gas emissions within the shale and the subsequent local/regional air quality impacts. Meteorological and trace gas instrumentation was deployed to Shape Ranch in southwestern Dimmit County, near the US/Mexico border, from April to November of 2015. Mixing ratios of CO, NO x , O 3 , and VOCs did not exceed ambient air quality standards and were generally lower than mixing ratios measured in US cities, with the exception of alkanes. A non-negative matrix factorization demonstrated the dominance of oil and gas-sector emission sources in local trace gas variability, with combustion processes and transport of continental air also present. An analysis of NO x /CO and NO x /CO 2 ratios during periods of O 3 titration, identified by the ambient NO x /O 3 ratio, suggested that combustion and biospheric sources contributed to emissions of NO x , CO, and CO 2 . In-plume NO x /CO 2 ratios indicated relatively low-temperature combustion sources, with median NO x /CO 2 ratios close to that expected for natural gas flaring (0.54 ppb/ppm), and much lower than emission ratios for internal combustion engines (>10 ppb/ppm). However, the NO x /CO 2 ratio within these plumes exhibited a large variability, spanning more than an order of magnitude. Future research should focus on improving flaring emission factors and flaring volume estimates such that their air quality impacts can be better understood.
Includes: Supplementary data
Journal Articles
Elementa: Science of the Anthropocene (2020) 8: 15.
Published: 16 April 2020
Abstract
Urban areas are recognised as a significant source of greenhouse gas emissions (GHG), such as carbon dioxide (CO 2 ) and methane (CH 4 ). The total amount of urban GHG emissions, especially for CH 4 , however, is not well quantified. Here we report on airborne in situ measurements using a Picarro G1301-m analyser aboard the DLR Cessna Grand Caravan to study GHG emissions downwind of the German capital Berlin. In total, five aircraft-based mass balance experiments were conducted in July 2018 within the Urban Climate Under Change [UC] 2 project. The detection and isolation of the Berlin plume was often challenging because of comparatively small GHG signals above variable atmospheric background concentrations. However, on July 20 th enhancements of up to 4 ppm CO 2 and 21 ppb CH 4 were observed over a horizontal extent of roughly 45 to 65 km downwind of Berlin. These enhanced mixing ratios are clearly distinguishable from the background and can partly be assigned to city emissions. The estimated CO 2 emission flux of 1.39 ± 0.76 t s –1 is in agreement with current inventories, while the CH 4 emission flux of 5.20 ± 1.70 kg s –1 is almost two times larger than the highest reported value in the inventories. We localized the source area with HYSPLIT trajectory calculations and the global/regional nested chemistry climate model MECO(n) (down to ~1 km), and investigated the contribution from sewage-treatment plants and waste deposition to CH 4 , which are treated differently by the emission inventories. Our work highlights the importance of strong CH 4 sources in the vicinity of Berlin and shows, that there is limited understanding of CH 4 emissions from urban regions, even for major cities in highly developed countries like Germany. Furthermore, we show that a detailed knowledge of GHG inflow mixing ratios is necessary to suitably estimate emission rates for Berlin.
Includes: Supplementary data
Journal Articles
Elementa: Science of the Anthropocene (2020) 8: 13.
Published: 24 March 2020
Abstract
The first Tropospheric Ozone Assessment Report (TOAR) provides information on present-day distributions and long-term trends of ozone metrics relevant for climate change, human health, and vegetation. However, only few results are available in TOAR for China due to limited long-term ozone observations. Here, we present an integrated analysis of long-term measurements of surface ozone from eight sites distributed in the North China Plain (NCP) and Yangtze River Delta (YRD), the relatively underdeveloped region Northeast China, and the remote regions in Northwest and Southwest China. Trends and present-day values for seven annual and five seasonal ozone metrics were calculated following the TOAR methodologies. We compare the seasonal and diurnal cycles of ozone concentrations as well as the present-day values of ozone among sites and discuss the long-term trends in the ozone metrics. Large and significant increases of ozone are detected at the background site in the NCP, moderate increases at the global baseline site in western China, significant decreases at the northwestern edge of China, and nearly no trend at other sites. Extremely high values of ozone occurred in the NCP and YRD, particularly in warmer seasons. The present-day levels of summer ozone metrics in the NCP are much higher than the thresholds set in TOAR for the highest value groups of ozone metrics. The summer ozone metrics at the Shangdianzi background site in the NCP indicate increases at rates of more than 2%/yr during 2004–2016. In contrast, ozone at the Lin’an background site in the YRD was constant over the period 2006–2016. Our results fill some knowledge gaps in spatiotemporal changes of ozone in China and may be of useful in the assessment of ozone impacts on human health and vegetation.
Includes: Supplementary data
Journal Articles
Elementa: Science of the Anthropocene (2020) 8: 7.
Published: 20 February 2020
Abstract
The Canadian federal government and the Province of Alberta (the dominant oil and gas producing province) have released competing methane regulations for the oil and gas sector intended to take effect between January 2020–2023. Provisions in Canadian law could allow the provincial regulations to take precedent, but only if they are deemed to be equivalent in effect. This paper presents a comprehensive technical comparison of these upcoming regulations by considering potential site-by-site mitigation impacts on active oil and gas facilities in Alberta in 2018. This analysis was made possible by first creating a detailed inventory using recent pneumatic device count data and current production and activity data, which allowed detailed site-level calculations of regulatory impacts on a monthly basis as required by the regulations. The federal regulations are found to be stronger, achieving ~26% more methane mitigation at full implementation. Key differences are in limits on pneumatic pump emissions, vented emissions, and expected reductions in fugitive emissions through leak detection and repair surveys. The full analysis was repeated using production and inventory data for 2012 and 2017 to examine sensitivities to changing production patterns and facilitate comparisons to the 2012 baseline referenced in federal policy targets for methane reduction. The results were robust in all scenarios. Through a “Potential to Emit” threshold, the federal regulations also impact slightly fewer sites overall by exempting small sites handling limited gas volumes, while achieving greater overall methane reductions. Relative to a 2012 baseline, if fully implemented in 2018 the federal regulations would just reach the bottom of the 40–45% methane reduction target through a combination of past reductions (13%) and additional regulated mitigation (27%). However, recent trends in emissions from mined oil sands operations in particular (which are not affected by these regulations) suggests the 40–45% reduction goal for the overall sector may not be achieved by the 2025 target. Different scenarios to make the regulations equivalent are briefly discussed where the contrast in achieved mitigations for different key sources is important case study data for design of effective and efficient methane regulations.
Includes: Supplementary data
Journal Articles
Elementa: Science of the Anthropocene (2020) 8: 4.
Published: 10 February 2020
Abstract
The rise of hydraulic fracturing techniques has fostered rapid growth of oil and natural gas (O&NG) extraction in areas across the United States. In the Denver-Julesburg Basin (DJB), which mostly overlaps with Weld County in the Northern Colorado Front Range (NCFR) north of the City of Denver Metropolitan Area (DMA), the well drilling has increasingly approached, and in many instances moved into urban residential areas. During the same time, the region has also experienced steady population growth. The DMA – NCFR has been in exceedance of the ozone U.S. National Ambient Air Quality Standard (NAAQS) and was designated a non-attainment area of the standard in 2007. Despite State efforts to curb precursors, ozone has consistently remained above the standard. A growing number of atmospheric studies has provided an ever increasing body of literature for assessing influences from O&NG industry emissions on air quality in the DMA-NCFR. This paper provides 1. An overview of available literature on O&NG influences on the regional air quality, 2. A summary of the pertinent findings presented in these works, 3. An assessment of the most important pollutants and air quality impacts, 4. Identification of knowledge and monitoring gaps, and 5. Recommendations for future research and policy.
Includes: Supplementary data
Journal Articles
Elementa: Science of the Anthropocene (2020) 8: 3.
Published: 13 January 2020
Abstract
The Seoul Metropolitan Area (SMA) has a population of 24 million and frequently experiences unhealthy levels of ozone (O 3 ). In this work, measurements taken during the Korea-United States Air Quality Study (KORUS-AQ, 2016) are used to explore regional gradients in O 3 and its chemical precursors, and an observationally-constrained 0-D photochemical box model is used to quantify key aspects of O 3 production including its sensitivity to precursor gases. Box model performance was evaluated by comparing modeled concentrations of select secondary species to airborne measurements. These comparisons indicate that the steady state assumption used in 0-D box models cannot describe select intermediate species, highlighting the importance of having a broad suite of trace gases as model constraints. When fully constrained, aggregated statistics of modeled O 3 production rates agreed with observed changes in O 3 , indicating that the box model was able to represent the majority of O 3 chemistry. Comparison of airborne observations between urban Seoul and a downwind receptor site reveal a positive gradient in O 3 coinciding with a negative gradient in NO x , no gradient in CH 2 O, and a slight positive gradient in modeled rates of O 3 production. Together, these observations indicate a radical-limited (VOC-limited) O 3 production environment in the SMA. Zero-out simulations identified C 7+ aromatics as the dominant VOC contributors to O 3 production, with isoprene and anthropogenic alkenes making smaller but appreciable contributions. Simulations of model sensitivity to decreases in NO x produced results that were not spatially uniform, with large increases in O 3 production predicted for urban Seoul and decreases in O 3 production predicted for far-outlying areas. The policy implications of this work are clear: Effective O 3 mitigation strategies in the SMA must focus on reducing local emissions of C 7+ aromatics, while reductions in NO x emissions may increase O 3 in some areas but generally decrease the regional extent of O 3 exposure.
Includes: Supplementary data
Journal Articles
Elementa: Science of the Anthropocene (2020) 8: 2.
Published: 10 January 2020
Abstract
Peak levels of ozone (O 3 )—quantified by concentration metrics such as accumulated O 3 exposure over a threshold of 40 ppb (AOT40) and the sigmoidal-weighted cumulative exposure (W126)—have decreased over large parts of the United States and Europe in the last several decades. Past studies have suggested that these improvements in AOT40 and W126 indicate reductions in plant injury, even though it is widely recognized that O 3 flux into leaves, not ambient O 3 concentration, is the cause of plant damage. Using a new dataset of O 3 uptake into plants derived from eddy covariance flux towers, we test whether AOT40, W126, or summer mean O 3 are useful indicators of trends in the cumulative uptake of O 3 into leaves, which is the phytotoxic O 3 dose (POD or POD y , where y is a detoxification threshold). At 32 sites in the United States and Europe, we find that the AOT40 and W126 concentration metrics decreased over 2005–2014 at most sites: 25 and 28 sites, respectively. POD 0 , however, increased at a majority (18) of the sites. Multiple statistical tests demonstrate that none of the concentration metrics—AOT40, W126, and mean O 3 —are good predictors of POD 0 temporal trends or variability ( R 2 ≤ 0.15). These results are insensitive to using a detoxification threshold (POD 3 ). The divergent trends for O 3 concentration and plant uptake are due to stomatal control of flux, which is shaped by environmental variability and plant factors. As a result, there has been no widespread, clear improvement in POD over 2005–2014 at the sites we can assess. Decreases in concentration metrics, therefore, give an overly optimistic and incomplete picture of the direction and magnitude of O 3 impacts on vegetation. Because of this lack of relation between O 3 flux and concentration, flux metrics should be preferred over concentration metrics in assessments of plant injury from O 3 .
Includes: Supplementary data
Journal Articles
Elementa: Science of the Anthropocene (2019) 7: 58.
Published: 30 December 2019
Abstract
The cryosphere, which comprises a large portion of Earth’s surface, is rapidly changing as a consequence of global climate change. Ice, snow, and frozen ground in the polar and alpine regions of the planet are known to directly impact atmospheric composition, which for example is observed in the large influence of ice and snow on polar boundary layer chemistry. Atmospheric inputs to the cryosphere, including aerosols, nutrients, and contaminants, are also changing in the anthropocene thus driving cryosphere-atmosphere feedbacks whose understanding is crucial for understanding future climate. Here, we present the Cryosphere and ATmospheric Chemistry initiative (CATCH) which is focused on developing new multidisciplinary research approaches studying interactions of chemistry, biology, and physics within the coupled cryosphere – atmosphere system and their sensitivity to environmental change. We identify four key science areas: (1) micro-scale processes in snow and ice, (2) the coupled cryosphere-atmosphere system, (3) cryospheric change and feedbacks, and (4) improved decisions and stakeholder engagement. To pursue these goals CATCH will foster an international, multidisciplinary research community, shed light on new research needs, support the acquisition of new knowledge, train the next generation of leading scientists, and establish interactions between the science community and society.
Includes: Supplementary data
Journal Articles
Elementa: Science of the Anthropocene (2019) 7: 56.
Published: 27 December 2019
Abstract
We examine O 3 production and its sensitivity to precursor gases and boundary layer mixing in Korea by using a 3-D global chemistry transport model and extensive observations during the KORea-US cooperative Air Quality field study in Korea, which occurred in May–June 2016. During the campaign, observed aromatic species onboard the NASA DC-8 aircraft, especially toluene, showed high mixing ratios of up to 10 ppbv, emphasizing the importance of aromatic chemistry in O 3 production. To examine the role of VOCs and NO x in O 3 chemistry, we first implement a detailed aromatic chemistry scheme in the model, which reduces the normalized mean bias of simulated O 3 mixing ratios from –26% to –13%. Aromatic chemistry also increases the average net O 3 production in Korea by 37%. Corrections of daytime PBL heights, which are overestimated in the model compared to lidar observations, increase the net O 3 production rate by ~10%. In addition, increasing NO x emissions by 50% in the model shows best performance in reproducing O 3 production characteristics, which implies that NO x emissions are underestimated in the current emissions inventory. Sensitivity tests show that a 30% decrease in anthropogenic NO x emissions in Korea increases the O 3 production efficiency throughout the country, making rural regions ~2 times more efficient in producing O 3 per NO x consumed. Simulated O 3 levels overall decrease in the peninsula except for urban and other industrial areas, with the largest increase (~6 ppbv) in the Seoul Metropolitan Area (SMA). However, with simultaneous reductions in both NO x and VOCs emissions by 30%, O 3 decreases in most of the country, including the SMA. This implies the importance of concurrent emission reductions for both NO x and VOCs in order to effectively reduce O 3 levels in Korea.
Includes: Supplementary data
Journal Articles
Elementa: Science of the Anthropocene (2019) 7: 57.
Published: 27 December 2019
Abstract
In an environment with many local, remote, persistent, and episodic sources of pollution, meteorology is the primary factor that drives periods of unhealthy air quality and reduced visibility. The 2016 Korea-United States Air Quality (KORUS-AQ) field study provides a unique opportunity to examine the impact of meteorology on the relative influence of local and transboundary pollution. Much of the KORUS-AQ campaign can be grouped into four distinct research periods based on observed synoptic meteorology, including a period of complex aerosol vertical profiles driven by dynamic meteorology, stagnation under a persistent anticyclone, low-level transport and haze development, and a blocking pattern. These episodes are examined using a diverse archive of ground, airborne, and satellite data. While frontal boundaries are recognized as the primary mechanism driving pollution transport in eastern Asia, results show that they are not always related to sustained periods of hazardous air quality and reduced visibility at the surface. Significant long-range transport of pollution and dust was constrained to a few short events, suggesting that the majority of pollutants sampled during KORUS-AQ originated from local sources. A severe regional pollution episode is examined in detail, featuring dense haze and significant secondary particle formation within a shallow moist boundary layer. Observations during KORUS-AQ also highlight a rapid, 40 ppbv increase in ozone pollution as a strong sea breeze front traversed the Seoul Metropolitan Area. Representativeness of meteorology and pollution conditions measured by KORUS-AQ is considered by comparison with climatology. This analysis is an essential step toward improved local and regional forecasting of air quality and visibility.
Includes: Supplementary data
Journal Articles
Elementa: Science of the Anthropocene (2019) 7: 49.
Published: 06 December 2019
Abstract
Germany and the United Kingdom have domestic shale gas reserves which they may exploit in the future to complement their national energy strategies. However gas production releases volatile organic compounds (VOC) and nitrogen oxides (NO x ), which through photochemical reaction form ground-level ozone, an air pollutant that can trigger adverse health effects e.g. on the respiratory system. This study explores the range of impacts of a potential shale gas industry in these two countries on local and regional ambient ozone. To this end, comprehensive emission scenarios are used as the basis for input to an online-coupled regional chemistry transport model (WRF-Chem). Here we simulate shale gas scenarios over summer (June, July, August) 2011, exploring the effects of varying VOC emissions, gas speciation, and concentration of NO x emissions over space and time, on ozone formation. An evaluation of the model setup is performed, which exhibited the model’s ability to predict surface meteorological and chemical variables well compared with observations, and consistent with other studies. When different shale gas scenarios were employed, the results show a peak increase in maximum daily 8-hour average ozone from 3.7 to 28.3 μg m –3 . In addition, we find that shale gas emissions can force ozone exceedances at a considerable percentage of regulatory measurement stations locally (up to 21% in Germany and 35% in the United Kingdom) and in distant countries through long-range transport, and increase the cumulative health-related metric SOMO35 (maximum percent increase of ~28%) throughout the region. Findings indicate that VOC emissions are important for ozone enhancement, and to a lesser extent NO x , meaning that VOC regulation for a future European shale gas industry will be of especial importance to mitigate unfavorable health outcomes. Overall our findings demonstrate that shale gas production in Europe can worsen ozone air quality on both the local and regional scales.
Includes: Supplementary data