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Accurate fire emissions inventories are crucial to predict the impacts of wildland fires on air quality and atmospheric composition. Two traditional approaches are widely used to calculate fire emissions: a satellite‐based top‐down approach and a fuels‐based bottom‐up approach. However, these methods often considerably disagree on the amount of particulate mass emitted from fires. Previously available observational datasets tended to be sparse, and lacked the statistics needed to resolve these methodological discrepancies. Here, we leverage the extensive and comprehensive airborne in situ and remote sensing measurements of smoke plumes from the recent Fire Influence on Regional to Global Environments and Air Quality (FIREX‐AQ) campaign to statistically assess the skill of the two traditional approaches. We use detailed campaign observations to calculate and compare emission rates at an exceptionally high‐resolution using three separate approaches: top‐down, bottom‐up, and a novel approach based entirely on integrated airborne in situ measurements. We then compute the daily average of these high‐resolution estimates and compare with estimates from lower resolution, global top‐down and bottom‐up inventories. We uncover strong, linear relationships between all of the high‐resolution emission rate estimates in aggregate, however no single approach is capable of capturing the emission characteristics of every fire. Global inventory emission rate estimates exhibited weaker correlations with the high‐resolution approaches and displayed evidence of systematic bias. The disparity between the low‐resolution global inventories and the high‐resolution approaches is likely caused by high levels of uncertainty in essential variables used in bottom‐up inventories and imperfect assumptions in top‐down inventories. Plain Language Summary: Smoke emitted by wildland fires is dangerous to human health and contributes to climate change. To predict and evaluate the impacts of fires, we need to know how much smoke is emitted into the atmosphere. There are two state‐of‐the‐art methods used to estimate the mass of smoke emitted by fires, but they often disagree. In this study, we use unusually detailed measurements collected using an aircraft that flew within wildland fire smoke plumes to calculate the amount of smoke emitted from fires in the Western United States. We compare emission rates derived from the exceptionally high spatial and temporal resolution approach to the two traditional, lower resolution approaches to understand why they sometimes diverge. Key Points: In situ measurements of wildland fire smoke plumes provide emission rates for evaluating emissions inventories at unprecedented resolutionFire emissions inventories struggle to capture the emissions rate characteristics of individual fires but may perform well in the aggregateBottom‐up inventories suffer from major uncertainty in key variables, while top‐down inventories may have bias from imperfect assumptions [ABSTRACT FROM AUTHOR]

The largest share in the climate impact of aviation results from contrail cirrus clouds. Here, the dependence of microphysical contrail ice properties and extinction on temperature and humidity is investigated. Contrail measurements were performed at various altitudes during the 2018 ECLIF II/NDMAX campaign with the NASA DC‐8 chasing the DLR A320. Ice number concentrations and contrail extinction coefficients are largest at altitudes near 9.5 km, typical for short‐ and medium‐range air traffic. At higher altitudes near 11.5 km, low ambient water vapor concentrations lead to smaller contrail particle sizes and lower extinction coefficients. In addition, contrails were detected below 8.2 km near the Schmidt‐Appleman contrail formation threshold temperature. Here, only a small fraction (<15%) of the emitted soot particles were activated into ice. Our observations enhance the understanding of contrail formation near the formation threshold and give a glimpse on the altitude dependence of climate‐relevant contrail properties. Plain Language Summary: Aviation has an impact on our climate and of all components, contrails are the main contributor. In January 2018, we measured contrails during the ECLIF II/NDMAX campaign. The NASA research aircraft DC‐8 flew closely behind the DLR's A320. With a wide range of instruments, we measured trace gases and soot particles emitted by the A320, as well as contrail ice crystals. The data presented here are the most comprehensive contrail data set ever collected during a single flight campaign. The contrail properties are strongly influenced by ambient parameters as well as aircraft and fuel properties. Here, we focus on the influence of environmental conditions such as temperature and humidity on the formation and growth of contrail ice crystals. Therefore, we present and compare ice measurements at three different flight altitudes. For 1–2‐min old contrails, we find a decrease in extinction with increasing altitude. Extinction describes the interaction between contrails and atmospheric radiation. We also find that at the lowest and warmest altitudes only a small part of the emitted soot particles is activated into contrail ice crystals. In the end, our data help to better understand contrail formation and will contribute to the research on sustainable aviation. Key Points: The dependence of contrail ice microphysics and extinction on ambient temperature and humidity is investigatedSoot activation fractions in contrails formed at varying ambient temperatures are derived of soot and apparent ice emission indicesAt altitudes below 8.2 km, we observed contrails formed under incomplete soot activation near the contrail formation threshold temperature [ABSTRACT FROM AUTHOR]

One‐second in situ measurements of CO and CO2 mole fractions were made aboard the National Aeronautics and Space Administration DC‐8 aircraft during the 2016 KORUS‐AQ joint air quality and atmospheric chemistry field campaign in South Korea. The ratio of CO to CO2 enhancement is used to characterize regional combustion source signatures. Calculations of the ∆CO/∆CO2 ratio were made with a short duration rolling window (60 s), filtered by the coefficient of determination (R2), and plotted as distributions to characterize air masses measured from the aircraft during the campaign. The KORUS‐AQ sampling domain was divided into analysis regions to facilitate the analysis. Over Seoul, the boundary layer shows a low‐ratio signature in the ∆CO/∆CO2 ratios, with more than 50% of the correlated slopes in the boundary layer falling below 1% ∆CO/∆CO2, and 80% of the slopes between 0% and 2% ∆CO/∆CO2. However, this behavior changes to a larger ratio distribution at higher altitudes. The West Sea receptor region was divided into three analysis sectors, by meteorological regime, and used in conjunction with measurements collected over China during the KORUS‐AQ campaign time period to characterize the Chinese ∆CO/∆CO2 ratio signature. Chinese‐type emissions have a slope distribution that is shifted to higher ratios and broadened compared to measurements over Seoul, with the bulk of the measurements between 2% and 4% ∆CO/∆CO2, with few negative slopes. The measured ratio trends over South Korea are consistent with inventoried CO and CO2 emissions. Plain Language Summary: Measurements of carbon monoxide (CO) and carbon dioxide (CO2) were made over South Korea in May and June of 2016. The ratio of CO to CO2 provides information about the combustion sources in a region, as most of the CO measured in the atmosphere is sourced from combustion, such as open air fires or engines. Using a 1‐s data set, the short‐term slopes of CO to CO2 enhancement were calculated by making a measurement of the CO to CO2 slope at every observation using the data in the surrounding minute. Plotting the distributions of the short‐term slopes with correlated values in the calculation window reveals whether the air masses have mostly low ratios of CO/CO2, which indicates high‐efficiency combustion, or mostly high ratios of CO/CO2, from low‐efficiency combustion. The slope distributions over the Seoul megacity show low‐ratio distributions, but at high altitudes the ratios move to higher values, showing that the combustion sources change with altitude and have a less efficient combustion signature. Meanwhile, the ratios that were measured over the West Sea show that the air coming to South Korea from China has higher CO/CO2 ratios than the air that is measured over South Korea. Key Points: Short‐term ∆CO/∆CO2 ratios characterized air masses measured by aircraft over South Korea during the 2016 KORUS‐AQ field campaignThe air mass combustion efficiency signature can be assessed with the distribution of the correlated short‐term CO to CO2 slopesDifferences were found between Chinese influenced and South Korea influenced air masses, which reflect the known sources in each country [ABSTRACT FROM AUTHOR]

A previous report documented that endocrine disrupting chemicals contribute substantially to certain forms of disease and disability. In the present analysis, our main objective was to update a range of health and economic costs that can be reasonably attributed to endocrine disrupting chemical exposures in the European Union, leveraging new burden and disease cost estimates of female reproductive conditions from accompanying report. Expert panels evaluated the epidemiologic evidence, using adapted criteria from the WHO Grading of Recommendations Assessment, Development and Evaluation Working Group, and evaluated laboratory and animal evidence of endocrine disruption using definitions recently promulgated by the Danish Environmental Protection Agency. The Delphi method was used to make decisions on the strength of the data. Expert panels consensus was achieved for probable (>20%) endocrine disrupting chemical causation for IQ loss and associated intellectual disability; autism; attention deficit hyperactivity disorder; endometriosis; fibroids; childhood obesity; adult obesity; adult diabetes; cryptorchidism; male infertility, and mortality associated with reduced testosterone. Accounting for probability of causation, and using the midpoint of each range for probability of causation, Monte Carlo simulations produced a median annual cost of €163 billion (1.28% of EU Gross Domestic Product) across 1000 simulations. We conclude that endocrine disrupting chemical exposures in the EU are likely to contribute substantially to disease and dysfunction across the life course with costs in the hundreds of billions of Euros per year. These estimates represent only those endocrine disrupting chemicals with the highest probability of causation; a broader analysis would have produced greater estimates of burden of disease and costs.

Earth's atmosphere oxidizes the greenhouse gas methane and other gases, thus determining their lifetimes and oxidation products. Much of this oxidation occurs in the remote, relatively clean free troposphere above the planetary boundary layer, where the oxidation chemistry is thought to be much simpler and better understood than it is in urban regions or forests. The NASA airborne Atmospheric Tomography study (ATom) was designed to produce cross sections of the detailed atmospheric composition in the remote atmosphere over the Pacific and Atlantic Oceans during four seasons. As part of the extensive ATom data set, measurements of the atmosphere's primary oxidant, hydroxyl (OH), and hydroperoxyl (HO2) are compared to a photochemical box model to test the oxidation chemistry. Generally, observed and modeled median OH and HO2 agree to within combined uncertainties at the 2σ confidence level, which is ~±40%. For some seasons, this agreement is within ~±20% below 6‐km altitude. While this test finds no significant differences, OH observations increasingly exceeded modeled values at altitudes above 8 km, becoming ~35% greater, which is near the combined uncertainties. Measurement uncertainty and possible unknown measurement errors complicate tests for unknown chemistry or incorrect reaction rate coefficients that would substantially affect the OH and HO2 abundances. Future analysis of detailed comparisons may yield additional discrepancies that are masked in the median values. Plain Language Summary: Chemistry in the vast, remote atmosphere destroys methane and other greenhouse gases. This chemistry is thought to be simple and well understood compared to that in polluted cities or in forests. From the NASA airborne Atmospheric Tomography study over remote oceans, comparisons of observed and modeled reactive gases show that the chemistry is generally understood to within the uncertainties of the measurement and model. However, for the atmosphere's primary reactive gas, hydroxyl, measured values exceed modeled values in the upper troposphere, pointing to errors in probably the measurements but possibly the model chemistry. Key Points: Free tropospheric hydroxyl and hydroperoxyl radical chemistry appears to be understood to within measurement and model uncertainty of ±40%Observed hydroxyl often exceeded modeled values in the upper troposphere, but measurement uncertainty masks any model chemistry errorsA hydroxyl measurement interference found in forests for this instrument does not exist throughout the free troposphere, even near convection [ABSTRACT FROM AUTHOR]

We examine the distribution and fate of nitrogen oxides (NOx) in the lower troposphere over the Northeast United States (NE US) using aircraft observations from the Wintertime INvestigation of Transport, Emissions, and Reactivity (WINTER) campaign in February–March 2015, as well as the GEOS‐Chem chemical transport model and concurrent ground‐based observations. We find that the National Emission Inventory from the U.S. Environmental Protection Agency is consistent with WINTER observations of total reactive nitrogen (TNOy) to within 10% on average, in contrast to the significant overestimate reported in past studies under warmer conditions. Updates to the dry deposition scheme and dinitrogen pentoxide (N2O5) reactive uptake probability, ɣ(N2O5), result in an improved simulation of gas‐phase nitric acid (HNO3) and submicron particulate nitrate (pNO3−), reducing the longstanding factor of 2–3 overestimate in wintertime HNO3 + pNO3− to a 50% positive bias. We find a NOx lifetime against chemical loss and deposition of 22 hr in the lower troposphere over the NE US. Chemical loss of NOx is dominated by N2O5 hydrolysis (58% of loss) and reaction with OH (33%), while 7% of NOx leads to the production of organic nitrates. Wet and dry deposition account for 55% and 45% of TNOy deposition over land, respectively. We estimate that 42% of the NOx emitted is exported from the NE US boundary layer during winter, mostly in the form of HNO3 + pNO3− (40%) and NOx (38%). Plain Language Summary: Nitrogen oxides are a key family of pollutants emitted by cars, electric utilities, and industry. The fate of nitrogen oxides remains poorly understood especially during the winter season, when low sunlight leads to their persistence in the atmosphere. We analyze comprehensive aircraft observations of nitrogen oxides and their atmospheric products over the Northeast United States during winter 2015. This detailed chemical information allows to resolve a long‐standing overestimate of the oxidation products of nitrogen oxides and places new constraints on their deposition to land ecosystems and export to the global atmosphere. Key Points: Existing anthropogenic NOx inventory is consistent with aircraft and ground‐based observations over Northeast United States during winterNOx has a 22 hr lifetime, with half of NOy present as NOx, 37% as HNO3 and pNO3−, and remaining 13% mostly as PANModel reproduces NOy partitioning and predicts a 42% NOx export efficiency in winter, with a 55–45% split between wet and dry deposition [ABSTRACT FROM AUTHOR]