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Isoprene is the dominant non-methane organic compound emitted to the atmosphere 1 – 3 . It drives ozone and aerosol production, modulates atmospheric oxidation and interacts with the global nitrogen cycle 4 – 8 . Isoprene emissions are highly uncertain 1 , 9 , as is the nonlinear chemistry coupling isoprene and the hydroxyl radical, OH—its primary sink 10 – 13 . Here we present global isoprene measurements taken from space using the Cross-track Infrared Sounder. Together with observations of formaldehyde, an isoprene oxidation product, these measurements provide constraints on isoprene emissions and atmospheric oxidation. We find that the isoprene–formaldehyde relationships measured from space are broadly consistent with the current understanding of isoprene–OH chemistry, with no indication of missing OH recycling at low nitrogen oxide concentrations. We analyse these datasets over four global isoprene hotspots in relation to model predictions, and present a quantification of isoprene emissions based directly on satellite measurements of isoprene itself. A major discrepancy emerges over Amazonia, where current underestimates of natural nitrogen oxide emissions bias modelled OH and hence isoprene. Over southern Africa, we find that a prominent isoprene hotspot is missing from bottom-up predictions. A multi-year analysis sheds light on interannual isoprene variability, and suggests the influence of the El Niño/Southern Oscillation. Direct satellite measurements of atmospheric isoprene are compared with model predictions, showing broad agreement but highlighting spatial and temporal biases in modelled isoprene and nitrogen oxide emissions.

Atmospheric methane growth reached an exceptionally high rate of 15.1 ± 0.4 parts per billion per year in 2020 despite a probable decrease in anthropogenic methane emissions during COVID-19 lockdowns(1). Here we quantify changes in methane sources and in its atmospheric sink in 2020 compared with 2019. We find that, globally, total anthropogenic emissions decreased by 1.2 ± 0.1 teragrams of methane per year (Tg CH4 yr−1), fire emissions decreased by 6.5 ± 0.1 Tg CH4 yr−1 and wetland emissions increased by 6.0 ± 2.3 Tg CH4 yr−1. Tropospheric OH concentration decreased by 1.6 ± 0.2 per cent relative to 2019, mainly as a result of lower anthropogenic nitrogen oxide (NOx) emissions and associated lower free tropospheric ozone during pandemic lockdowns(2). From atmospheric inversions, we also infer that global net emissions increased by 6.9 ± 2.1 Tg CH4 yr−1 in 2020 relative to 2019, and global methane removal from reaction with OH decreased by 7.5 ± 0.8 Tg CH4 yr−1. Therefore, we attribute the methane growth rate anomaly in 2020 relative to 2019 to lower OH sink (53 ± 10 per cent) and higher natural emissions (47 ± 16 per cent), mostly from wetlands. In line with previous findings(3,4,) our results imply that wetland methane emissions are sensitive to a warmer and wetter climate and could act as a positive feedback mechanism in the future. Our study also suggests that nitrogen oxide emission trends need to be taken into account when implementing the global anthropogenic methane emissions reduction pledge(5).

Associations between long-term exposure to nitrogen oxides (NO x ) and cause-specific mortality remain insufficiently explored. This study utilizes data from 502,040 participants registered in the UK Biobank. Time-varying Cox regression is used to estimate mortality risks associated with NO x . Cause-specific mortality risks, including non-accidental, accidental and 15 major disease categories across 103 subcategories, are assessed for each 10 μg/m 3 increase in NO x . Positive associations are observed between NO x and mortality from all-cause (HR: 1.036; 95% CI: 1.024, 1.049) and non-accidental diseases (HR: 1.032; 95% CI: 1.019, 1.045). We further identify 20 specific diseases related to NO x , notably respiratory diseases, mental and behavioral disorders, and circulatory diseases, with generally linear exposure-response relationships. Sex and residential areas are potential modifiers of the observed associations. Our findings suggest long-term exposure to NO x may increase mortality risks from a range of diseases, emphasizing the urgent need for clean air policies to alleviate the health burden. There is a critical gap in understanding the full spectrum of health effects associated with NO x exposure. Here, the authors find using UK Biobank data that mortality from all-cause, non-accidental and other 20 specific diseases was significantly associated with NO x .

Rapid development of agriculture and fossil fuel combustion greatly increased US reactive nitrogen emissions to the atmosphere in the second half of the 20th century, resulting in excess nitrogen deposition to natural ecosystems. Recent efforts to lower nitrogen oxides emissions have substantially decreased nitrate wet deposition. Levels of wet ammonium deposition, by contrast, have increased in many regions. Together these changes have altered the balance between oxidized and reduced nitrogen deposition. Across most of the United States, wet deposition has transitioned from being nitrate-dominated in the 1980s to ammonium-dominated in recent years. Ammonia has historically not been routinely measured because there are no specific regulatory requirements for its measurement. Recent expansion in ammonia observations, however, along with ongoing measurements of nitric acid and fine particle ammonium and nitrate, permit new insight into the balance of oxidized and reduced nitrogen in the total (wet + dry) US nitrogen deposition budget. Observations from 37 sites reveal that reduced nitrogen contributes, on average, ∼65% of the total inorganic nitrogen deposition budget. Dry deposition of ammonia plays an especially key role in nitrogen deposition, contributing from 19% to 65% in different regions. Future progress toward reducing US nitrogen deposition will be increasingly difficult without a reduction in ammonia emissions.

Aircraft measurements, laboratory photolysis experiments and modelling calculations reveal a mechanism for the recycling of nitric acid into nitrogen oxides; this enables observations to be reconciled with model studies, and suggests that particulate nitrate photolysis could be a substantial tropospheric nitrogen oxide source. Rapid NO x recycling in marine air Nitrogen oxides play a central role in tropospheric chemistry, but current understanding of the processes responsible for their formation and removal from the atmosphere is insufficient to reconcile model studies with observations. This paper presents aircraft measurements, laboratory photolysis experiments and modelling calculations that reveal a mechanism for the rapid recycling of nitric acid to nitrous acid and nitrogen oxides in the clean marine boundary layer via particulate nitrate photolysis. The authors suggest that this process could be an important tropospheric nitrogen oxide source in remote oceanic regions with implications for tropospheric oxidant and secondary atmospheric aerosol formation. Nitrogen oxides are essential for the formation of secondary atmospheric aerosols and of atmospheric oxidants such as ozone and the hydroxyl radical, which controls the self-cleansing capacity of the atmosphere 1 . Nitric acid, a major oxidation product of nitrogen oxides, has traditionally been considered to be a permanent sink of nitrogen oxides 1 . However, model studies predict higher ratios of nitric acid to nitrogen oxides in the troposphere than are observed 2 , 3 . A ‘renoxification’ process that recycles nitric acid into nitrogen oxides has been proposed to reconcile observations with model studies 2 , 3 , 4 , but the mechanisms responsible for this process remain uncertain 5 , 6 , 7 , 8 , 9 . Here we present data from an aircraft measurement campaign over the North Atlantic Ocean and find evidence for rapid recycling of nitric acid to nitrous acid and nitrogen oxides in the clean marine boundary layer via particulate nitrate photolysis. Laboratory experiments further demonstrate the photolysis of particulate nitrate collected on filters at a rate more than two orders of magnitude greater than that of gaseous nitric acid, with nitrous acid as the main product. Box model calculations based on the Master Chemical Mechanism 10 , 11 suggest that particulate nitrate photolysis mainly sustains the observed levels of nitrous acid and nitrogen oxides at midday under typical marine boundary layer conditions. Given that oceans account for more than 70 per cent of Earth’s surface, we propose that particulate nitrate photolysis could be a substantial tropospheric nitrogen oxide source. Recycling of nitrogen oxides in remote oceanic regions with minimal direct nitrogen oxide emissions could increase the formation of tropospheric oxidants and secondary atmospheric aerosols on a global scale.

N2O is a powerful greenhouse gas contributing both to global warming and ozone depletion. While fungi have been identified as a putative source of N2O, little is known about their production of this greenhouse gas. Here we investigated the N2O-producing ability of a collection of 207 fungal isolates. Seventy strains producing N2O in pure culture were identified. They were mostly species from the order Hypocreales order—particularly Fusarium oxysporum and Trichoderma spp.—and to a lesser extent species from the orders Eurotiales, Sordariales, and Chaetosphaeriales. The N2O 15N site preference (SP) values of the fungal strains ranged from 15.8‰ to 36.7‰, and we observed a significant taxa effect, with Penicillium strains displaying lower SP values than the other fungal genera. Inoculation of 15 N2O-producing strains into pre-sterilized arable, forest and grassland soils confirmed the ability of the strains to produce N2O in soil with a significant strain-by-soil effect. The copper-containing nitrite reductase gene (nirK) was amplified from 45 N2O-producing strains, and its genetic variability showed a strong congruence with the ITS phylogeny, indicating vertical inheritance of this trait. Taken together, this comprehensive set of findings should enhance our knowledge of fungi as a source of N2O in the environment.

The concentration of fine particulate matter (PM 2.5 ) across China has decreased by 30–50% over the period 2013–2018 due to stringent emission controls. However, the nitrate component of PM 2.5 has not responded effectively to decreasing emissions of nitrogen oxides and has actually increased during winter haze pollution events in the North China Plain. Here, we show that the GEOS-Chem atmospheric chemistry model successfully simulates the nitrate concentrations and trends. We find that winter mean nitrate would have increased over 2013–2018 were it not for favourable meteorology. The principal cause of this nitrate increase is weaker deposition. The fraction of total inorganic nitrate as particulate nitrate instead of gaseous nitric acid over the North China Plain in winter increased from 90% in 2013 to 98% in 2017, as emissions of nitrogen oxides and sulfur dioxide decreased while ammonia emissions remained high. This small increase in the particulate fraction greatly slows down deposition of total inorganic nitrate and hence drives the particulate nitrate increase. Our results suggest that decreasing ammonia emissions would decrease particulate nitrate by driving faster deposition of total inorganic nitrate. Decreasing nitrogen oxide emissions is less effective because it drives faster oxidation of nitrogen oxides and slower deposition of total inorganic nitrate. Reduction of ammonia emissions may be effective in reducing the nitrate component of fine particulate matter air pollution across the North China Plain, according to the simulation of nitrate trends using the GEOS-Chem atmospheric chemistry model.

Background Substantial differences in preterm birth (PTB) persist across populations, with African Americans facing the highest rate. While air pollution contributes to PTB, its role in these uneven health burdens remains poorly understood. Studies of PTB subtypes might uncover racial variation in etiology, yet the impact of air pollution is largely understudied. We assessed the associations of prenatal exposures to ambient fine particulate matters (PM 2.5 ), carbon monoxide (CO), and nitrogen oxides (NO x ) with PTB and its subtypes using data from the Atlanta African American Maternal-Child Cohort. Methods We conducted a prospective analysis among 567 African Americans with singleton pregnancies and without chronic medical conditions. Live births were divided into three categories: PTB, early term birth (ETB), and full-term birth, and PTB was further classified into: spontaneous (i.e., sPTB) and medically indicated (i.e., miPTB). Additionally, a composite category combining PTB and ETB was analyzed. We estimated residential air pollution exposures during five critical windows: 1 month prior to conception, entire pregnancy, the 1 st , 2 nd , and 3 rd trimesters. We performed logistic models and discrete-time survival models for individual air pollutants and quantile g-computation models to evaluate the overall effect, with adjustment of selected covariates. We further evaluated whether infant sex modified the associations between gestational air pollution exposure and PTB risk. Results PM 2.5 exposure during the 1 st trimester showed a non-significant trend toward increased PTB risk (OR: 1.50, 95% CI: 0.96–2.35). PM 2.5 exposure showed significant associations with miPTB during the 2 nd trimester (OR: 1.90, 95%CI: 1.03–3.43). Air pollution mixture models showed similar trends, particularly for miPTB. Also, PM 2.5 exposure had stronger effects on early birth (PETB, PTB + ETB), with the largest effect observed across the entire pregnancy (OR: 1.44, 95%CI: 0.90–2.10). Air pollution mixture was significantly associated with increased odds of PETB (OR: 1.33, 95%CI: 1.03–1.72) during the 2 nd trimester. We found no evidence that the associations between air pollution exposure and PTB differed by infant sex. Discussion Our findings suggested that prenatal air pollution exposure, particularly to PM 2.5 during early gestational periods, could elevate miPTB risk and early birth among African Americans.

Fine particulate matter (PM2.5) decreased by 30–40% across China during 2013–2017 in response to the governmental Clean Air Action. However, surface ozone pollution worsened over the same period. Model simulations have suggested that the increase in ozone could be driven by the decrease in PM2.5, because PM2.5 scavenges hydroperoxy (HO2) and NOx radicals that would otherwise produce ozone. Here we show observational evidence for this effect with 2013–2018 summer data of hourly ozone and PM2.5 concentrations from 106 sites in the North China Plain. The observations show suppression of ozone pollution at high PM2.5 concentrations, consistent with a model simulation in which PM2.5 scavenging of HO2 and NOx depresses ozone concentrations by 25 ppb relative to PM2.5-free conditions. PM2.5 chemistry makes ozone pollution less sensitive to NOx emission controls, emphasizing the need for controlling emissions of volatile organic compounds (VOCs), which so far have not decreased in China. The new 2018–2020 Clean Air Action plan calls for a 10% decrease in VOC emissions that should begin to reverse the long-term ozone increase even as PM2.5 continues to decrease. Aggressive reduction of NOx and aromatic VOC emissions should be particularly effective for decreasing both PM2.5 and ozone.

Learning more about how pollutants enter and damage the body would reduce disease and deaths, say Jos Lelieveld and Ulrich Pöschl. Learning more about how pollutants enter and damage the body would reduce disease and deaths, say Jos Lelieveld and Ulrich Pöschl.