The multiscale, complex challenges at the nexus of food, energy, and water systems (FEWS) demand approaches to graduate education beyond traditional disciplinary training. Here, we present a vision for training FEWS leaders developed by faculty and students from interdisciplinary graduate training programs focused on the FEWS nexus. We discuss the imperative to create interdisciplinary, next-generation FEWS leaders and the core skills and proficiencies such leaders need: employ systems thinking, thrive in interdisciplinary teams, communicate effectively, and engage diverse stakeholders and communities. These skills will prepare students to connect science to innovative, actionable solutions and to successfully lead across a variety of careers. Graduate training that integrates these approaches must, on the one hand, overcome structural, cultural, and financial barriers in higher education, but on the other hand, will help develop a community of practice capable of developing sustainable solutions for the FEWS nexus and other vexing environmental challenges.

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.

Changing complexity in the increasingly integrated human, natural, and built systems within which our infrastructures are designed and operated make it necessary to examine how the role of engineering requires new competencies for satisficing. Several long-term trends appear to be shifting our infrastructures further away from the complicated domain where optimization and efficiency were the core approaches, to the domain of complexity, where rapidly changing environments and fragmentation of goals require fundamentally new approaches. While complexity in infrastructure has always existed in some form, making infrastructures agile and flexible for the Anthropocene will require us to acknowledge and work with the fact that infrastructure change now appears to be a wicked and complex process. Wicked complexity is the result of three competing forces that are inimical to rapid and sustained change of infrastructures in a future marked by acceleration and uncertainty: wicked problems, technical complexity including lock-in, and social complexity. The combination of these factors raises serious questions about whether rapidly changing demands, technologies, and perturbations (such as climate change, or cyber attacks) will affect our infrastructure’s capacity to provide services. What infrastructure managers need to do today is very different than in the past. Increased presence and polarization of viewpoints is becoming more common, where solutions are dictated not by technical performance measures but instead by “acceptable enough” to all parties. Adaptive management practices and associated competencies that have proven successful in managing complex socio-ecological systems may provide some guidance for how to manage infrastructure change. These competencies are i) promoting a shared understanding of what infrastructures can do, ii) managing infrastructures as systems with changing demands, iii) emphasizing experimentation over conventional approaches, and, iv) restructuring education and training for a complexity mindset that emphasizes what can be over what is, and relies on satisficing, not optimization.

Data from ground-based ozone (O 3 ) vertical profiling platforms operated during the FRAPPE/DISCOVER-AQ campaigns in summer 2014 were used to characterize key processes responsible for establishing O 3 profile development in the boundary layer in the Northern Colorado Front Range. Morning mixing from the upper boundary layer and lower free troposphere into the lower boundary layer was the key process establishing the mid-morning boundary layer O 3 mixing ratio. Photochemical O 3 production throughout the boundary layer builds on the mid-morning profile. From late morning to mid-afternoon the continuing O 3 increase was nearly uniform through the depth of the profile measured by the tethersonde (~400 m). Ozonesondes flown on a near daily schedule over a four week period with multiple profiles on a number of days captured the full 1500 to 2000 m vertical extent of O 3 enhancements in the mixed boundary layer confirming O 3 production throughout the entire boundary layer. Continuous O 3 measurements from the Boulder Atmospheric Observatory (BAO) tall tower at 6 m and 300 m showed hourly O 3 at the 6 m level ≥75 ppb on 15% of the days. The diurnal variation on these days followed a pattern similar to that seen in the tethersonde profiles. The association of high O 3 days at the BAO tower with transport from sectors with intense oil and natural gas production toward the northeast suggests emissions from this industry were an important source of O 3 precursors and are crucial in producing peak O 3 events in the NCFR. Higher elevation locations to the west of the NCFR plains regularly experience higher O 3 values than those in the lower elevation NCFR locations. Exposure of populations in these areas is not captured by the current regulatory network, and likely underestimated in population O 3 exposure assessments.

The total solar eclipse on August 21, 2017, provided a rare opportunity to observe and test our understanding of atmospheric dynamics and photochemical dependency on solar irradiance. Here, we utilize observations from the continuous monitoring of both slow and fast photochemically reacting trace gases near Boulder, Colorado, for evaluating the unique dynamic and photochemical forcings on the eclipse day. The monitoring station saw a 93% solar obstruction during the peak of the eclipse. Eclipse day data are contrasted with the full month’s record from this site. The loss of irradiance caused cooling of the surface air by ~3°C, and weakened convective and turbulent mixing. This resulted in a buildup of slow photoreactive gases (methane, short-chain non-methane hydrocarbons), as well as total nitrogen oxides (the sum of nitric oxide (NO) + nitrogen dioxide (NO 2 )) in the surface layer. In contrast, ozone (O 3 ) declined by ~15 ppb during the first phase of the eclipse compared to median August diurnal mixing ratios. Similar O 3 signatures were observed at a series of network stations along the Northern Colorado Front Range. With the loss of irradiance, the initial ratio of NO/(NO + NO 2 ) of ~0.2 dropped steadily, bottoming out at <0.01, but rebounded to approximately two times above August median levels for this time of day towards the end of the eclipse. Above average O 3 enhancements were seen in the afternoon hours following the eclipse at this and a series of other nearby surface O 3 monitoring sites. The contrasting behavior of these slow and fast photoreactive gases, and comparison with other published eclipse data, allow characterizing these responses as more typical for an urban/polluted environment.

In 2016, the Denver Metro Area (DMA)/Northern Colorado Front Range (NCFR) was reclassified from a Marginal to a Moderate O 3 Non-Attainment Area due to the prevalence of high summer ozone (O 3 ) occurrences. Hourly surface O 3 data collected during 2000–2015 from a total of 80 monitoring sites in the State of Colorado were investigated for geographical features in O 3 behavior and O 3 changes over time. We particularly focus on summer O 3 (June, July, August), which is the time when most exceedances of the O 3 National Ambient Air Quality Standard (NAAQS) have been recorded. Variables investigated include the statistical (5 th , 50 th (median), and 95 th percentile) distribution of O 3 mixing ratios, diurnal amplitudes, and their trends. Trend analyses were conducted for 20 site records that had at least ten years of data. The majority of Colorado ozone monitoring sites show an increase of the 5 th (16 total; 11 of these are statistically significant (p-value ≤ 0.05) trends) and 50 th (15 total; 4 statistically significant trends) percentile values. Changes for the 95 th percentile values were smaller and less consistent. One site showed a statistically significant declining trend, and one site an increasing trend; the majority of other sites had slightly negative, albeit not statistically significant declining O 3 . Ozone changes at the two highest elevations sites (>2500 m asl) are all negative, contrasting increasing O 3 at U.S. West Coast sites. NCFR urban sites do not show the rate of decreasing higher percentile O 3 as seen for the majority of urban areas across the U.S. during the past 1–2 decades. The amplitudes of diurnal O 3 cycles were studied as a proxy for nitrogen oxides (NO x ) emissions and the diurnal O 3 production chemistry. The majority of sites show a decrease in the median summer O 3 diurnal amplitude (19 total/10 statistically significant). This is mostly driven by the increase in nighttime O 3 minima, which is most likely a sign for a declining rate of nighttime O 3 loss from titration with nitric oxide (NO), indicating a change in O 3 behavior from declining NO x emissions. Since median and upper percentile surface O 3 values in the DMA have not declined at the rates seen in other western U.S. regions, thus far the reduction in NO x has had a more pronounced effect on the lower percentile O 3 distribution than on high O 3 occurrences that primarily determine air quality. An assessment of the influence of oil and gas emissions on Colorado, and in particular DMA O 3 , is hampered by the sparsity of monitoring within oil and gas basins. Continuous, long-term, high quality, and co-located O 3 , NO x , and VOC monitoring are recommended for elucidating the geographical heterogeneity of O 3 precursors, their changing emissions, and for evaluation of the effectiveness of O 3 air quality regulations.

In support of the first Tropospheric Ozone Assessment Report (TOAR) a relational database of global surface ozone observations has been developed and populated with hourly measurement data and enhanced metadata. A comprehensive suite of ozone data products including standard statistics, health and vegetation impact metrics, and trend information, are made available through a common data portal and a web interface. These data form the basis of the TOAR analyses focusing on human health, vegetation, and climate relevant ozone issues, which are part of this special feature. Cooperation among many data centers and individual researchers worldwide made it possible to build the world’s largest collection of in-situ hourly surface ozone data covering the period from 1970 to 2015. By combining the data from almost 10,000 measurement sites around the world with global metadata information, new analyses of surface ozone have become possible, such as the first globally consistent characterisations of measurement sites as either urban or rural/remote. Exploitation of these global metadata allows for new insights into the global distribution, and seasonal and long-term changes of tropospheric ozone and they enable TOAR to perform the first, globally consistent analysis of present-day ozone concentrations and recent ozone changes with relevance to health, agriculture, and climate. Considerable effort was made to harmonize and synthesize data formats and metadata information from various networks and individual data submissions. Extensive quality control was applied to identify questionable and erroneous data, including changes in apparent instrument offsets or calibrations. Such data were excluded from TOAR data products. Limitations of a posteriori data quality assurance are discussed. As a result of the work presented here, global coverage of surface ozone data for scientific analysis has been significantly extended. Yet, large gaps remain in the surface observation network both in terms of regions without monitoring, and in terms of regions that have monitoring programs but no public access to the data archive. Therefore future improvements to the database will require not only improved data harmonization, but also expanded data sharing and increased monitoring in data-sparse regions.

Ten-year observations of trace gases at Pico Mountain Observatory (PMO), a free troposphere site in the central North Atlantic, were classified by transport patterns using the Lagrangian particle dispersion model, FLEXPART. The classification enabled identifying trace gas mixing ratios associated with background air and long- range transport of continental emissions, which were defined as chemical signatures. Comparison between the chemical signatures revealed the impacts of natural and anthropogenic sources, as well as chemical and physical processes during long transport,on air composition in the remote North Atlantic. Transport of North American anthropogenic emissions(NA-Anthro) and summertime wildfire plumes (Fire) significantly enhanced CO and O 3 at PMO. Summertime CO enhancements caused by NA-Anthro were found to have been decreasing by a rate of 0.67 ± 0.60 ppbv/year in the ten-year period, due possibly to reduction of emissions in North America. Downward mixing from the upper troposphere and stratosphere due to the persistent Azores-Bermuda anticyclone causes enhanced O 3 and nitrogen oxides. The d [O 3 ]/ d [CO] value was used to investigate O 3 sources and chemistry in different transport patterns. The transport pattern affected by Fire had the lowest d [O 3 ]/ d [CO], which was likely due to intense CO production and depressed O 3 production in wildfire plumes. Slightly enhanced O 3 and d [O 3 ]/ d [CO] were found in the background air, suggesting that weak downward mixing from the upper troposphere is common at PMO. Enhancements of both butane isomers were found during upslope flow periods, indicating contributions from local sources. The consistent ratio of butane isomers associated with the background air and NA-anthro implies no clear difference in the oxidation rates of the butane isomers during long transport. Based on observed relationships between non-methane hydrocarbons, the averaged photochemical age of the air masses at PMO was estimated to be 11 ± 4 days.

Instrumented aircraft measuring air composition in the Uinta Basin, Utah, during February 2012 and January-February 2013 documented dramatically different atmospheric ozone (O 3 ) mole fractions. In 2012 O 3 remained near levels of ∼40 ppb in a well-mixed 500–1000 m deep boundary layer while in 2013, O 3 mole fractions >140 ppb were measured in a shallow (∼200 m) boundary layer. In contrast to 2012 when mole fractions of emissions from oil and gas production such as methane (CH 4 ), non-methane hydrocarbons (NMHCs) and combustion products such as carbon dioxide (CO 2 ) were moderately elevated, in winter 2013 very high mole fractions were observed. Snow cover in 2013 helped produce and maintain strong temperature inversions that capped a shallow cold pool layer. In 2012, O 3 and CH 4 and associated NMHCs mole fractions were not closely related. In 2013, O 3 mole fractions were correlated with CH 4 and a suite of NMHCs identifying the gas field as the primary source of the O 3 precursor NMHC emissions. In 2013 there was a strong positive correlation between CH 4 and CO 2 suggesting combustion from oil and natural gas processing activities. The presence of O 3 precursor NMHCs through the depth of the boundary layer in 2013 led to O 3 production throughout the layer. In 2013, O 3 mole fractions increased over the course of the week-long episodes indicating O 3 photochemical production was larger than dilution and deposition rates, while CH 4 mole fractions began to level off after 3 days indicative of some air being mixed out of the boundary layer. The plume of a coal-fired power plant located east of the main gas field was not an important contributor to O 3 or O 3 precursors in the boundary layer in 2013.

Trace gas measurements from whole air samples collected weekly into glass flasks at background monitoring sites within the NOAA Global Greenhouse Gas Reference Network program (with most of the sites also being World Meteorological Organization (WMO) Global Atmospheric Watch (GAW) stations) were used to investigate the variability-lifetime relationship for site characterization and to estimate regional and seasonal OH concentrations. Chemical species considered include the atmospheric trace gases CO, H 2 , and CH 4 , as well as the non-methane hydrocarbons (NMHC) ethane (C 2 H 6 ), propane (C 3 H 8 ), i -butane ( i -C 4 H 10 ), and n -butane ( n -C 4 H 10 ). The correlation between atmospheric variability and lifetime was applied on a global scale spanning 42 sites with observations covering a period of 5 years. More than 50,000 individual flask measurement results were included in this analysis, making this the most extensive study of the variability-lifetime relationship to date. Regression variables calculated from the variability-lifetime relationship were used to assess the “remoteness” of sampling sites and to estimate the effect of local pollution on the measured distribution of atmospheric trace gases. It was found that this relationship yields reasonable results for description of the site remoteness and local pollution influences. Comparisons of seasonal calculated OH concentrations ([OH]) from the variability-lifetime relationships with six direct station measurements yielded variable agreement, with deviations ranging from ∼20% to a factor of ∼2–3 for locations where [OH] monitoring results had been reported. [OH] calculated from the variability-lifetime relationships was also compared to outputs from a global atmospheric model. Resutls were highly variable, with approximately half of the sites yielding agreement to within a factor of 2–3, while others showed deviations of up to an order of magnitude, especially during winter.

Electric power is required to produce, treat, distribute, and recycle water while water is required to generate and consume electricity. Naturally, this energy-water nexus is most evident in multi-utilities that provide electricity and water but still exists when the nexus has distinct organizations as owners and operators. Therefore, the sustainability question that arises from energy-water trade-offs and synergies is very much tied to the potential for economies of scope. Furthermore, in the Middle East and North Africa (MENA) region, multi-utilities are not only common, but also the nexus is particularly exacerbated by the high energy intensity of the water supply due to limited fresh water resources. The goal of this paper is to identify and motivate several opportunities for enhanced integrated operations management and planning in the energy-water nexus in multi-utilities in the MENA. It proceeds in four parts. First, an exposition of the energy-water nexus especially as it applies to the MENA is given. This discussion focuses on the electric power system, the potable water distribution system, and thirdly, the wastewater distribution system. Second, the paper shifts to opportunities in integrated operations management highlighted by an energy-water nexus supply- side economic dispatch illustration. Thirdly, the discussion shifts to planning opportunities for the energy-water nexus for the sustainable development of water and energy resources. A concluding section summarizes the policy implications of the identified opportunities.

Long-term observations of reactive gases in the troposphere are important for understanding trace gas cycles and the oxidation capacity of the atmosphere, assessing impacts of emission changes, verifying numerical model simulations, and quantifying the interactions between short-lived compounds and climate change. The World Meteorological Organization’s (WMO) Global Atmosphere Watch (GAW) program coordinates a global network of surface stations some of which have measured reactive gases for more than 40 years. Gas species included under this umbrella are ozone, carbon monoxide, nitrogen oxides, and volatile organic compounds (VOCs). There are many challenges involved in setting-up and maintaining such a network over many decades and to ensure that data are of high quality, regularly updated and made easily accessible to users. This overview describes the GAW surface station network of reactive gases, its unique quality management framework, and discusses the data that are available from the central archive. Highlights of data use from the published literature are reviewed, and a brief outlook into the future of GAW is given. This manuscript constitutes the overview of a special feature on GAW reactive gases observations with individual papers reporting on research and data analysis of particular substances being covered by the program.

A record spanning ten years of non-methane hydrocarbon (NMHC) data from the Pico Mountain Observatory (PMO), Pico Island, Azores, Portugal, was analyzed for seasonal NMHC behavior, atmospheric processing, and trends, focusing on ethane and propane. The location of this site in the central North Atlantic, at an elevation of 2225 m asl, allows these data to be used to investigate the background conditions and pollution transport events occurring in the lower free North Atlantic troposphere. The quantity ln([propane]/[ethane]) was used as an indicator of both photochemical processing and a marker for the occurrence of pollution transport events detected at the station. The Pico data were compared with three other continuous NMHC data sets from sites bordering the North Atlantic, i.e. the Global Atmospheric Watch (GAW) stations at Summit, Greenland, Hohenpeisssenberg, Germany, and Cape Verde, using ln([propane]/[ethane]) results as an indicator for the degree of photochemical processing (‘aging’) seen in the data. Comparisons of these three data sets showed some significant differences in the seasonal background and range of observed values. The statistical distribution of binned monthly data was determined, and individual sample events were then scaled to the monthly median observed value. Back trajectories, determined by the HYSPLIT model were used to investigate the geographic origin of the observed trace gases as a function of the degree of photochemical processing. Results show that PMO samples have been subjected to a diversity of air transport and aging, from highly processed air to freshly emitted air throughout the year, and in particular during summer months. The predominant air transport is from North America, with only occasional influence from continental areas located east and southeast (Europe and Africa). The available record was found to be too variable and still too short to allow deciphering NMHC trends from the data. Ethane and propane measurements at the PMO were compared with the MOZART-4 atmospheric chemistry and transport model at the appropriate time and location. The model was found to yield good agreement in the description of the lower range of atmospheric mole fractions observed, of the seasonal cycle, and the regional oxidation chemistry. However, ethane and propane enhancements in transport events were underestimated, indicating that after the ≥ 3 days of synoptic transport to PMO the spatial extent of plumes frequently is smaller than the 2.8°x2.8° (∼300 km) model grid resolution.

The Northern Front Range (NFR) region of Colorado has experienced rapid expansion of oil and gas extraction from shale and tight sands reservoirs in recent years due to advances in hydraulic fracturing technology, with over 25,000 wells currently in operation. This region has also been designated as a federal ozone non-attainment area by the U.S. EPA. High ozone levels are a significant health concern, as are potential health impacts from chronic exposure to primary emissions of non-methane hydrocarbons (NMHC) for residents living near wells. From measurements of ambient atmospheric NMHC present in residential areas located in close proximity to wells in Erie, Colorado, we find that mean mole fractions of the C2–C5 alkanes are enhanced by a factor of 18–77 relative to the regional background, and present at higher levels than typically found in large urban centers. When combined with NMHC observations from downtown Denver and Platteville, it is apparent that these compounds are elevated across the NFR, with highest levels within the Greater Wattenberg Gas Field. This represents a large area source for ozone precursors in the NFR. The BTEX aromatic compounds in Erie were comparable to (e.g., benzene) or lower than (e.g., toluene, ethylbenzene, xylene) in large urban centers, however, benzene was significantly higher in Platteville, and within the range of chronic health-based exposure levels. An initial look at comparisons with data sets from previous years reveal that ambient levels for oil and gas-related NMHC in Erie, as well as further downwind in Boulder, have not decreased, but appear to have been increasing, despite tightening of emissions standards for the oil and gas industries in 2008.