The 50 most-cited articles in Atmospheric chemistry and physics, 2024

Abstract. The global annual mean radiative forcing (RF) attributable to contrail cirrus is comparable to the RF from aviation’s cumulative CO2 emissions. Here, we simulate the global contrail climate forcing for 2019–2021 using reanalysis weather data and improved engine emission estimates along actual flight trajectories derived from Automatic Dependent Surveillance–Broadcast telemetry. Our 2019 global annual mean contrail net RF (62.1 mW m-2) is 44 % lower than current best estimates for 2018 (111 [33, 189] mW m-2). Regionally, the contrail net RF is largest over Europe (876 mW m-2) and the US (414 mW m-2), while the RF over East Asia (64 mW m-2) and China (62 mW m-2) are close to the global mean value because fewer flights in these regions form contrails as a result of lower cruise altitudes and limited ice supersaturated regions in the subtropics due to the Hadley Circulation. Globally, COVID-19 reduced the flight distance flown and contrail net RF in 2020 (-43 % and -56 % respectively vs. 2019) and 2021 (-31 % and -49 % respectively) with significant regional variation. Around…

Abstract. Powering aircraft by sustainable aviation fuels (SAF) is a pathway to reduce the climate impact of aviation by lowering aviation life-cycle CO2 emissions and by reducing ice crystal numbers and radiative forcing from contrails. While the effect of SAF blends on contrails has been measured previously, here we present novel measurements on particle emission and contrails from 100 % SAF combustion. During the ECLIF3 (Emission and CLimate Impact of alternative Fuels) campaign, a collaboration between DLR, AIRBUS, ROLLS-ROYCE and NESTE, the DLR Falcon 20 research aircraft performed in situ measurements following an Airbus A350-941 source aircraft powered by Rolls-Royce Trent XWB-84 engines in 1 to 2 min old contrails at cruise altitudes. Apparent ice emission indices of 100 % HEFA-SPK (Hydro-processed Esters and Fatty Acids - Synthetic Paraffinic Kerosene) were measured and compared to Jet A-1 fuel contrails at similar engine and ambient ice-supersaturated conditions within a single flight. A 56 % reduction of ice particle numbers per mass of burned fuel was measured for 100 %…

Abstract. Aviation emissions that are dispersed into the Earth's atmosphere affect the climate and air pollution, with significant spatiotemporal variation owing to heterogeneous aircraft activity. In this paper, we use historical flight trajectories derived from Automatic Dependent Surveillance–Broadcast (ADS-B) telemetry and reanalysis weather data for 2019–2021 to develop the Global Aviation emissions inventory based on ADS-B (GAIA). In 2019, 40.2 million flights collectively travelled 61 billion kilometres using 283 Tg of fuel, leading to CO2, NOX, non-volatile particulate matter (nvPM) mass and number emissions of 893 Tg, 4.49 Tg, 21.4 Gg, and 2.8×1026, respectively. Global responses to COVID-19 led to reductions in the annual flight distance flown, CO2, and NOX emissions in 2020 (-43 %, -48 % and -50 %, respectively relative to 2019) and 2021 (-31 %, -41 % and -43 %, respectively) with significant regional variability. Short-haul flights with duration < 3 h accounted for 83 % of all flights, yet only for 35 % of the 2019 CO2 emissions, while long-haul flights with duration > 6…

Abstract. Although air quality guidelines generally use the atmospheric concentration of fine particulate matter (PM2.5) as a metric for air pollution evaluation and management, the fact cannot be ignored that different particle toxicities are unequal and significantly related to their sources and chemical compositions. Therefore, judging the most harmful source and identifying the toxic component would be helpful for optimizing air quality standards and prioritizing targeted PM2.5 control strategies to protect public health more effectively. Since the combustions of fuels, including oil, coal, and biomass, are the main anthropogenic sources of environmental PM2.5, their discrepant contributions to health risks of mixed ambient aerosol pollution dominated by the respective emission intensity and unequal toxicity of chemical components need to be identified. In order to quantify the differences between these combustion primary emissions, 10 types of PM2.5 from each typical source group, i.e., vehicle exhaust, coal combustion, and plant biomass (domestic biofuel) burning, were…

Abstract. We quantify 2019 methane emissions in the contiguous U.S. (CONUS) at 0.25° × 0.3125° resolution by inverse analysis of atmospheric methane columns measured by the Tropospheric Monitoring Instrument (TROPOMI). A gridded version of the U.S. Environmental Protection Agency (EPA) Greenhouse Gas Emissions Inventory (GHGI) serves as the basis for the prior estimate for the inversion. We optimize emissions and quantify observing system information content for an eight-member inversion ensemble through analytical minimization of a Bayesian cost function. We achieve high resolution with a reduced-rank characterization of the observing system that optimally preserves information content. Our optimal (posterior) estimate of anthropogenic emissions in CONUS is 30.9 (30.0–31.8) Tg a-1, where the values in parentheses give the spread of the ensemble. This is a 13 % increase from the 2023 GHGI estimate for CONUS in 2019. We find livestock emissions of 10.4 (10.0–10.7) Tg a-1, oil and gas of 10.4 (10.1–10.7) Tg a-1, coal of 1.5 (1.2–1.9) Tg a-1, landfills of 6.9 (6.4–7.5) Tg a-1,…

Abstract. During the winters of the 2020–2022 period, several intense North African dust intrusions affected Europe. Some of them displayed a duration never recorded before. They were referred to as exceptional by several international operational and research institutions considering that wintertime is the season with minimum dust activity in the Mediterranean and Europe. These anomalous winter events with origin in North Africa largely affected western Mediterranean. The main objective of the present work is to analyse the atmospheric drivers (synoptic and large-scale environments) of wintertime (from January to March) dust events over the region covering North Africa, the Western Mediterranean and the Euro-Atlantic during the period 2003–2022. Overall, our results indicate large interannual variability over the study period. A dust catalogue of dust events identified by aerosols retrievals from satellite and aerosol reanalysis products shows a very irregular record and large differences between winter months. The analyses demonstrate a positive anomaly in dust concentration and…

Abstract. Biogenic volatile organic compounds (BVOCs) are important precursors to ozone and secondary organic aerosols in the atmosphere, affecting air quality, clouds and climate. However, the trend of BVOC emissions and driving factors for the emission changes in different geographic regions over the past two decades has remained unclear. Here, regional to global changes in BVOC emissions during 2001–2020 are simulated using the latest Model of Emission of Gases and Aerosols from Nature (MEGANv3.2) with the input of time-varying satellite-retrieved vegetation and reanalysis meteorology data. Comparison of model simulations with the site observations shows that the model can reasonably reproduce the magnitude of isoprene and monoterpene emission fluxes. The spatial distribution of the modeled isoprene emissions is generally comparable to the satellite retrievals. The estimated annual average global BVOC emissions are 835.4 Tg yr-1 with the emissions from isoprene, monoterpenes, sesquiterpenes, and other BVOC comprised of 347.7, 184.8, 23.3, and 279.6 Tg yr-1, respectively. We find…

Abstract. The MIXv2 Asian emission inventory is developed under the framework of the Model Inter-Comparison Study for Asia (MICS-Asia) Phase IV, and produced from a mosaic of up-to-date regional emission inventories. We estimated the emissions for anthropogenic and biomass burning sources covering 23 countries and regions in East, Southeast and South Asia, and aggregated emissions to a uniform spatial and temporal resolution for seven sectors: power, industry, residential, transportation, agriculture, open biomass burning and shipping. Compared to MIXv1, we extended the dataset to 2010 – 2017, included emissions of open biomass burning and shipping, and provided model-ready emissions of SAPRC99, SAPRC07, and CB05. A series of unit-based point source information was incorporated covering power plants in China and India. A consistent speciation framework for Non-Methane Volatile Organic Compounds (NMVOCs) was applied to develop emissions by three chemical mechanisms. The total Asian emissions for anthropogenic | open biomass sectors in 2017 are estimated as follows: 41.6 | 1.1 Tg NOx,…

Abstract. Extensive airborne measurements of non-methane organic gases (NMOGs), methane, nitrogen oxides, reduced nitrogen-species, and aerosol emissions from US wild and prescribed fires were conducted during the 2019 NOAA/NASA Fire Influence on Regional to Global Environments and Air Quality campaign (FIREX-AQ). Here, we report the atmospheric enhancement ratios (ERs) and inferred emission factors (EFs) for compounds measured onboard the NASA DC-8 research aircraft for nine wildfires and one prescribed fire, which encompass a range of vegetation types. We use photochemical proxies to identify young smoke and reduce the effects of chemical degradation on our emissions calculations. ERs and EFs calculated from FIREX-AQ observations agree within a factor of 2 with values reported from previous laboratory and field studies for more than 80 % of the carbon- and nitrogen-containing species. Wildfire emissions are parameterized based on correlations of the sum of NMOGs with reactive nitrogen oxides (NOy) to modified combustion efficiency (MCE) as well as other chemical signatures…

Tropospheric ozone results from in situ chemical formation and stratosphere–troposphere exchange (STE), with the latter being more important in the middle and upper troposphere than in the lower troposphere. Ozone photochemical formation is nonlinear and results from the oxidation of methane and non-methane hydrocarbons (NMHCs) in the presence of nitrogen oxide (NO x =NO+NO 2 ). Previous studies showed that O 3 short- and long-term trends are nonlinearly controlled by near-surface anthropogenic emissions of carbon monoxide (CO), volatile organic compounds (VOCs), and nitrogen oxides, which may also be impacted by the long-range transport (LRT) of O 3 and its precursors. In addition, several studies have demonstrated the important role of STE in enhancing ozone levels, especially in the midlatitudes. In this article, we investigate tropospheric ozone spatial variability and trends from 2005 to 2019 and relate those to ozone precursors on global and regional scales. We also investigate the spatiotemporal characteristics of the ozone formation regime in relation to ozone chemical…

Abstract. Global-mean surface temperature rapidly increased 0.27 ± 0.05 K from 2022 to 2023. Such an interannual global warming spike is not unprecedented in the observational record with previous instances occurring in 1956–57 and 1976–77. However, why global warming spikes occur is unknown and the rapid global warming of 2023 has led to concerns that it could have been externally driven. Here we show that climate models that are subject only to internal variability can generate such spikes, but they are an uncommon occurrence (𝑝 = 2.6 ± 0.1 %). However, when a prolonged La Niña immediately precedes an El Niño in the simulations, as occurred in nature in 1956–57, 1976–77, 2022–23, such spikes become much more common (𝑝 = 16.5 ± 0.6 %). Furthermore, we find that nearly all simulated spikes (94 %) are associated with El Niño occurring that year. Thus, our results underscore the importance of El Niño/Southern Oscillation in driving the occurrence of global warming spikes such as the one in 2023, without needing to invoke anthropogenic forcing, such as changes in atmospheric…

Abstract. Accelerating progress in climate modeling is urgent for proactive and effective climate change adaptation. The central challenge lies in accurately representing processes that are small in scale yet are climatically important, such as turbulence and cloud formation. These processes are not explicitly resolvable, necessitating the use of parameterizations. We propose a balanced approach that leverages the strengths of traditional process-based parameterizations and contemporary AI-based data-driven methods to model subgrid-scale processes. This strategy focuses on employing AI to derive data-driven closure functions from both observational and simulated data, integrated within parameterizations that encode system knowledge and conservation laws. Increasing resolution to resolve a larger fraction of small-scale processes can aid progress toward improved and interpretable climate predictions outside the observed climate distributions, but it must still allow the generation of large ensembles for model calibration and the broad exploration of possible climate outcomes –…

Abstract. Cooking is a source volatile organic compounds (VOCs) that degrades air quality. Cooking VOCs have been investigated in laboratory and indoor studies, but the contribution of cooking to the spatial and temporal variability of urban VOCs is uncertain. In this study, a proton-transfer-reaction time-of-flight mass spectrometer (PTR-ToF-MS) is used to identify and quantify cooking emission in Las Vegas, NV with supplemental data from Los Angeles, CA and Boulder, CO. Mobile laboratory data show that long-chain aldehydes, such as octanal and nonanal, are significantly enhanced in restaurant plumes and regionally enhanced in areas of Las Vegas with high restaurant density. Correlation analyses show that long-chain fatty acids are also associated with cooking emissions and the relative VOC enhancements observed in regions with dense restaurant activity are very similar to the distribution of VOCs observed in laboratory cooking studies. Positive matrix factorization (PMF) is used to quantify cooking emissions from ground site measurements and compare the magnitude of cooking to…

Abstract. Tropical tropospheric ozone (TTO) is important for the global radiation budget because the longwave radiative effect of tropospheric ozone is higher in the tropics than mid-latitudes. In recent decades the TTO burden has increased, partly due to the ongoing shift of ozone precursor emissions from mid-latitude regions toward the equator. In this study, we assess the distribution and trends of TTO using ozone profiles measured by high quality in situ instruments from the IAGOS (In-Service Aircraft for a Global Observing System) commercial aircraft, the SHADOZ (Southern Hemisphere ADditional OZonesondes) network, and the ATom (Atmospheric Tomographic Mission) aircraft campaign, as well as six satellite records reporting tropical tropospheric column ozone (TTCO): TROPOMI, OMI, OMI/MLS, OMPS/MERRA2, CrIS, and IASI/GOME2. With greater availability of ozone profiles across the tropics we can now demonstrate that tropical India is among the most polluted regions (e.g., Western Africa, tropical South Atlantic, Southeast Asia, Malaysia/Indonesia) with present-day 95th percentile…

Abstract. Ozone (O3) has become one of the most concerning air pollutants in China in recent decades. In this study, based on surface observations, reanalysis data, global atmospheric chemistry model simulations, and multi-model future predictions, meteorological characteristics conducive to extreme O3 pollution in various regions of China are investigated, and their historical changes and future trends are analyzed. During the most severe O3 polluted months, the chemical production of O3 is enhanced under the hot and dry conditions over the North China Plain (NCP) in June 2018 and the Yangtze River Delta (YRD) in July 2017, while regional transport is the main reason for the severe O3 pollution over the Sichuan Basin (SCB) in July 2015 and the Pearl River Delta (PRD) in September 2019. Over the last 4 decades, the frequencies of high-temperature and low-relative-humidity conditions increased in 2000–2019 relative to 1980–1999, indicating that O3 pollution in both the NCP and YRD has become more frequent under historical climate change. In the SCB and PRD, the occurrence of…

Abstract. Winter fog and severe aerosol loading in the boundary layer over north India, especially in the Indo-Gangetic Plain (IGP), cause disruption in the daily lives of millions of people in the region. To understand better the role of atmospheric aerosols on the occurrence, spatial extent, and persistence of winter fog in the IGP, several model simulations have been performed using the Weather Research and Forecasting model coupled with chemistry (WRF-Chem). Results from WRF-Chem represented relative humidity (RH) and fog formation in agreement with observations when using the ERA-Interim reanalysis data as meteorological initial/boundary conditions and soil nudging were applied. WRF-Chem successfully simulates the spatial distribution and magnitude of PM2.5 when evaluated with observations from the Central Pollution Control Board of India (CPCB) monitoring network. However, the aerosol composition predicted by WRF-Chem was quite different from measurements obtained during the Winter Fog Experiment (WiFEX) in Delhi, with chloride aerosol fraction being strongly underpredicted…

Abstract. Under the influence of climate change, the increasing occurrence of extreme weather events, such as heatwaves, has led to an enhanced frequency of ozone (O3) pollution issues. In August 2022, the Sichuan Basin (SCB), a typical large-scale geographical terrain located in southwestern China, experienced the most severe heatwave over the last 20 years. The heatwave led to substantial disparities in O3 levels across the region. Here, by integrating observations, machine learnings and numerical simulations, we aim to understand the diverse O3 formation mechanisms in two mega cities, Chengdu (western location) and Chongqing (eastern location). Observational data showed that Chengdu experienced a consecutive 17-day period of O3 exceedance, in contrast to Chongqing, where O3 concentrations remained below the standard. Meteorological and precursor factors were assessed, spotlighting high temperatures, intense solar radiation, and overnight accumulative pollutants as key contributors to O3 concentrations. The interplay of isoprene, temperature, and O3, alongside the…

Abstract. We summarise current important and well-established open issues related to the depletion of stratospheric ozone and discuss some newly emerging challenges. The ozone layer is recovering from the effects of halogenated source gases due to the continued success of the Montreal Protocol despite recent renewed production of controlled substances and the impact of uncontrolled very short-lived substances. The increasing atmospheric concentrations of greenhouse gases, such as carbon dioxide, methane (CH4) and nitrous oxide (N2O), have large potential to perturb stratospheric ozone in different ways, but their future evolutions, and hence impacts, are uncertain. Ozone depletion through injection of smoke particles has been observed following recent Australian wildfires. Further perturbations to the ozone layer are currently occurring through the unexpected injection of massive amounts of water vapour from the Hunga Tonga–Hunga Ha'apai volcano in 2022. Open research questions emphasise the critical need to maintain, if not expand, the observational network and to address the…

Abstract. Ozone (O3) pollution research and management in China have mainly focused on anthropogenic emissions, while the importance of natural processes is often overlooked. With the increasing frequency of extreme weather events, the role of natural processes in exacerbating O3 pollution is gaining attention. In September 2022, the Pearl River Delta (PRD) in South China experienced an extended period (25 days) of regional O3 exceedances and high temperatures (2nd highest over last 2 decades) due to extreme weather conditions influenced by the Subtropical High and typhoon peripheries. Employing an integrated approach involving field measurements, machine learning, and numerical model simulations, we investigated the impact of weather-induced natural processes on O3 pollution by considering meteorological factors, natural emissions, chemistry pathways, and atmospheric transport. It was found that the hot weather significantly promoted regional photochemical reactions, with meteorological factors contributing to an additional 10.8 ppb of O3 levels compared to normal conditions.…

Abstract. As air pollution is regarded as the single largest environmental health risk in Europe it is important that communication to the public is up-to-date, accurate and provides means to avoid exposure to high air pollution levels. Long- as well as short-term exposure to outdoor air pollution is associated with increased risks of mortality and morbidity. Up-to-date information on present and coming days’ air quality help people avoid exposure during episodes with high levels of air pollution. Air quality forecasts can be based on deterministic dispersion modelling, but to be accurate this requires detailed information on future emissions, meteorological conditions and process oriented dispersion modelling. In this paper we apply different machine learning (ML) algorithms – Random forest (RF), Extreme Gradient Boosting (XGB) and Long-Short Term Memory (LSTM) – to improve 1-, 2- and 3-day deterministic forecasts of PM10, NOx, and O3 at different sites in Greater Stockholm, Sweden. It is shown that the deterministic forecasts can be significantly improved using the MLs but that…

Abstract. Anthropogenic mercury (Hg) emissions to the atmosphere are a long-lived hazard to human and environmental health. The UN Minamata Convention on Mercury is seeking to lower anthropogenic mercury emissions through a mix of policies from banning Hg uses and trade, to reducing unintentional Hg releases from different activities. In addition to independent Hg policy, greenhouse gas, particulate matter (PM) and SO2 reduction policies may also lower Hg emissions as a co-benefit. This study uses the Greenhouse Gas – Air Pollution Interactions and Synergies (GAINS) model to examine the effect of different clean air and climate policy on future global Hg emissions. The Baseline scenario assumes current energy use and Hg emissions, as well as current legislation for clean air, mercury and climate policy. In addition, we explore the impact of the Minamata Convention, co-benefits of climate policies and of stringent air pollution policies, as well as a maximum feasible reduction scenario for Hg (Hg-MFR). Hg emission projections until 2050 show noticeable reductions in combustion…

Abstract. The global warming is amplified in the Arctic. To collect data that help to constrain weather and climate models, which often do not realistically represent the enhanced Arctic warming, the HALO-(AC)³ aircraft campaign was conducted in March and April 2022 over the Norwegian and Greenland Seas, the Fram Strait, and the central Arctic Ocean. Observations were made over areas of open ocean, the marginal sea ice zone, and the central Arctic sea ice. Two low-flying and one long-range, high-altitude research aircraft have been employed. Whenever possible, the three aircraft were flown in collocated formation. The campaign focused on one specific challenge posed by the models: The reasonable representation of transformations of air masses during their meridional transport into (northward by moist and warm air intrusions, WAIs) and out of (southward via marine cold air outbreaks, CAOs) the Arctic. To observe the air mass transformations, a quasi-Lagrangian flight strategy using trajectory calculations was realized enabling to sample the moving air mass parcels twice along their…

Abstract. General circulation models' (GCMs) estimates of the liquid water path adjustment to anthropogenic aerosol emissions differ in sign from other lines of evidence. This reduces confidence in estimates of the effective radiative forcing of the climate by aerosol–cloud interactions (ERFaci). The discrepancy is thought to stem in part from GCMs' inability to represent the turbulence–microphysics interactions in cloud-top entrainment, a mechanism that leads to a reduction in liquid water in response to an anthropogenic increase in aerosols. In the real atmosphere, enhanced cloud-top entrainment is thought to be the dominant adjustment mechanism for liquid water path, weakening the overall ERFaci. We show that the latest generation of GCMs includes models that produce a negative correlation between present-day cloud droplet number and liquid water path, a key piece of observational evidence supporting liquid water path reduction by anthropogenic aerosols and one that earlier-generation GCMs could not reproduce. However, even in GCMs with this negative correlation, the increase in…

Abstract. Accurate estimation of the wind profile, especially in the lowest few hundred meters of the atmosphere, is of great significance for weather, climate and renewable energy. Nevertheless, the Monin–Obukhov similarity theory fails above the surface layer over the heterogeneous underlying surface, resulting in an unreliable wind profile obtained from the conventional extrapolation methods. To solve this problem, we propose a novel method that combines the power law method (PLM) with the random forest (RF) algorithm to extend wind profiles beyond the surface layer, called the Phy-RF method. The underlying principle is to treat the wind profile as a power law distribution in the vertical direction, in which the power law exponent (α) is determined by the Phy-RF model. First, the Phy-RF model is constructed based on the atmosphere sounding data at 119 radiosonde (RS) stations across China and in conjunction with other data such as surface wind speed, land cover type, surface roughness, friction velocity, geographical location, and meteorological parameters from June 2020 to May…

Abstract. More than 2 decades ago, aerosol remote sensing underwent a revolution with the launch of the Terra and Aqua satellites. Advancement continued via additional launches carrying new passive and active sensors. Capable of retrieving parameters characterizing aerosol loading, rudimentary particle properties and in some cases aerosol layer height, the satellite view of Earth's aerosol system came into focus. The modeling communities have made similar advances. Now the efforts have continued long enough that we can see developing trends in both the remote sensing and modeling communities, allowing us to speculate about the future and how the community will approach aerosol remote sensing 20 years from now. We anticipate technology that will replace today's standard multi-wavelength radiometers with hyperspectral and/or polarimetry, all viewing at multiple angles. These will be supported by advanced active sensors with the ability to measure profiles of aerosol extinction in addition to backscatter. The result will be greater insight into aerosol particle properties. Algorithms…

Abstract. Unprecedented extreme Saharan-dust (duxt) events have recently expanded northward, from subtropical NW Africa to the NE Atlantic and SW Europe, affecting the Canary Islands and mainland Spain. These six historic duxt episodes occurred 3–5 February 2020, 22–29 February 2020, 15–21 February 2021, 14–17 January 2022, 29 January–1 February 2022 and 14–20 March 2022. We analysed data of 330 Governmental Air Quality Monitoring Stations (AQMSs) of Spain, where PM10 and PM2.5 are measured with European EN-standards, and found that during duxt events PM10 concentrations are underestimated due to technical limitations of some PM10 monitors to properly measure extremely high concentrations. We assessed the consistency of PM10 and PM2.5 data and reconstructed 1414 PM10 (1 h average) data of 48 AQMSs by using our novel duxt-r method. During duxt events, 1-hour average PM10 and PM2.5 concentrations were within the range 1000–6000 μg/m3 and 400–1200 μg/m3, respectively. The meteorological and dust modelling-reanalyses show that the intense winds leading to massive dust plumes occurred…

Abstract. Emissions from wildfires are a significant source of air pollution, which can adversely impact air quality and ecosystems thousands of kilometers downwind. These emissions can be estimated by a bottom-up approach, using inputs such fuel type, burned area, and standardized emission factors. Emissions are also commonly derived with a top-down approach, using satellite observed fire radiative power (FRP) as proxy for fuel consumption. More recently, wildfire emissions have been demonstrated to be estimated directly from satellite observations, including carbon monoxide (CO). Here, we explore the potential of satellite-derived CO emission rates from wildfires and provide new insights into the understanding of satellite-derived fire CO emissions globally, with respect to differences in regions and vegetation type. Specifically, we use the TROPOMI (Tropospheric Monitoring Instrument) high spatial-resolution satellite datasets to create a global inventory database of burning emissions CO emissions between 2019 and 2021. Our retrieval methodology includes an analysis of conditions…

Abstract. Nitrogen oxide radicals (NOx ≡ NO + NO2) emitted by fuel combustion are important precursors of ozone and particulate matter pollution, and NO2 itself is harmful to public health. The Geostationary Environment Monitoring Spectrometer (GEMS), launched in space in 2020, now provides hourly daytime observations of NO2 columns over East Asia. This diurnal variation offers unique information on the emission and chemistry of NOx, but it needs to be carefully interpreted. Here we investigate the drivers of the diurnal variation of NO2 observed by GEMS during winter and summer over Beijing and Seoul. We place the GEMS observations in the context of ground-based column observations (Pandora instruments) and GEOS-Chem chemical transport model simulations. We find good agreement between the diurnal variations of NO2 columns in GEMS, Pandora, and GEOS-Chem, and we use GEOS-Chem to interpret these variations. NOx emissions are four times higher in the daytime than at night, driving an accumulation of NO2 over the course of the day, offset by losses from chemistry and transport…

Abstract. Assessing the role of physical processes in the stratosphere under climate change has been one of the hottest topics over the past few decades. However, due to the limitation of detection technique, the stratospheric disturbance information from in situ observation is still relatively scarce. The round-trip intelligent sounding system (RTISS) is a new detection technology developed in recent years, which can capture atmospheric fine structure information of the troposphere and stratosphere through the three-stage (rising, flat-floating, and falling) detection. Based on the structure function and singular measure, we quantify the stratospheric small-scale gravity wave (SGW) over China by Hurst parameter and intermittency parameter, and discuss its relationship with inertia-gravity wave (IGW). The results show that the enhancement of the SGWs in the stratosphere is accompanied by the weakening of the IGWs below, which is closely related to the Kelvin-Helmholtz instability (KHI), and is conducive to the transport of ozone to higher altitudes from lower stratosphere. The…

Abstract. Interfacial and multiphase chemical processes involving gases typically involve adsorption and desorption onto liquid or solid substrates. The desorption energy, which depends on the intermolecular forces between adsorbate and substrate, determines the residence time of chemical species at the interface. In this study, we demonstrate how variations in desorption energy and temperature influence the net uptake or release of gas species, which in turn affects the rates of surface and bulk reactions, surface-bulk exchange, and the equilibration time scales of gas-particle partitioning. We survey experimentally and theoretically derived desorption energies to develop a parameterization that enables the prediction of desorption energies based on the molecular weight, polarizability, and oxygen to carbon ratio of the desorbing chemical species independent of substrate-specific properties, which is possible because of the dominating role of the desorbing species’ polarizability. The data and analyses compiled in this study provide new insights into the relationship between…

Abstract. Severe seasonal air pollution events have become frequent over northern India, particularly over the Indo-Gangetic Plain (IGP). These episodic hazes, marked by exceedingly high levels of ambient PM2.5 (particulate matter having an aerodynamic diameter ≤ 2.5 microns), are hazardous for visibility and public health. It is therefore imperative to examine the capabilities of current state-of-the-art coupled meteorology-chemistry models at predicting air quality over this region. We provide a comprehensive evaluation of WRF-Chem (v4.2.1) simulated seasonal meteorology and aerosol chemistry (PM2.5 and its black carbon (BC) component) using a range of ground-based, satellite and reanalysis products, with a focus on the November 2016 haze episode. Daily and diurnal features in simulated 2 m temperature show best agreement followed by relative humidity with overall low biases. Upper air meteorology comparisons with radiosonde observations show excellent model skill in reproducing the vertical temperature gradient (r > 0.95). Both ground and radiosonde observations confirm…

Abstract. In order to reduce aviation’s CO2 emissions and comply with current climate targets, the European Union plans a mandatory quota of 2 % sustainable aviation fuel (SAF) by 2025, rising up to ≥ 70 % SAF by 2050. In addition to a reduction of life cycle CO2-emissions the use of SAF can also have a positive impact on particle emissions and contrail properties. In this study we present observations from the ECLIF3 (Emission and CLimate Impact of alternative Fuels) aircraft campaign, which investigated exhaust and contrail characteristics of an Airbus A350-941 equipped with Rolls-Royce Trent XWB-84 engines. For the first time, non-volatile and total particle emissions of 100 % HEFA-SPK (Hydro-processed Esters and Fatty Acids – Synthetic Paraffinic Kerosene) SAF, a blended fuel and a reference Jet A-1 were measured in flight. A maximum reduction in non-volatile particle number emissions of ∼41 % compared to the reference Jet A-1 fuel was measured at low cruise engine power settings when using 100 % HEFA-SPK. The reduction decreases to ∼29 % for typical cruise engine settings and…

Abstract. The particle-phase state is crucial for reactive gas uptake, heterogeneous, and multiphase chemical reactions, thereby impacting secondary aerosol formation. This study provides valuable insights into the significance of particle-phase transition and aerosol liquid water (ALW) in winter particulate growth. Our findings reveal that particles predominantly exist as semi-solid or solid during clean winter days with ambient relative humidity (RH) below 30 %. However, non-liquid to liquid phase transition occurs when the ALW mass fraction exceeds 15 % (dry mass) at transition RH thresholds of 40–60 %. During haze episodes, the transformation rates of sulfate and nitrate aerosols rapidly increase through phase transition and increased ALW by 48 % and 11 %, respectively, resulting in noticeable increases in secondary inorganic aerosols (SIA). The presence of abundant ALW, favored by elevated RH and higher proportion of SIA, facilitates heterogeneous and aqueous processes in liquid particles, leading to a substantial increase in the formation of secondary organic aerosols and…

Abstract. Nitrogen oxides, emitted from air traffic, are of concern due to their impact on climate by changing atmospheric ozone and methane levels. Using the DLR research aircraft Falcon, total reactive nitrogen (NOy) measurements were carried out at high altitudes to characterize emissions in the fresh aircraft exhaust from the latest generation Rolls-Royce Trent XWB-84 engine aboard the long-range Airbus A350-941 aircraft. The impact of different engine thrust settings, monitored in terms of combustor inlet temperature, pressure, and engine fuel flow, was tested for two different fuel types: Jet A-1 and for the first time a 100 % sustainable aviation fuel (SAF) under similar atmospheric conditions. During ground emission measurements, a range of combustor temperatures and an additional blended SAF were tested. We confirm that the NOx emission index increases with increasing combustion temperature, pressure and fuel flow. We find that as expected, the fuel type has no measurable effect on the NOx emission index. These measurements are used to compare to cruise NOx emission index…

Abstract. Volatile organic compounds (VOCs) and particulate matter (PM) are major constituents of smog. Delhi experiences severe smog during post-monsoon season, but a quantitative understanding of VOCs and PM sources is still lacking. Here, we source-apportioned VOCs and PM, using a high-quality recent (2022) dataset of 111 VOCs, PM2.5, and PM10 using positive matrix factorization. Contrasts between clean-monsoon and polluted-post-monsoon air, VOC source fingerprints, molecular-tracers, enabled differentiating paddy-residue burning from other biomass-burning sources, which has hitherto been impossible. Fresh paddy-residue burning and residential heating & waste-burning contributed the highest to observed PM10 (25 % & 23 %), PM2.5 (23 % & 24 %), followed by heavy-duty CNG-vehicles 15 % PM10 and 11 % PM2.5. For ambient VOCs, ozone, and SOA formation potentials, top sources were petrol-4-wheelers (20 %, 25 %, 30 %), petrol-2-wheelers (14 %, 12 %, 20 %), mixed-industrial emissions (12 %, 14 %, 15 %), solid fuel-based cooking (10 %, 10 %, 8 %) and road construction (8 %, 6 %, 9 %).…

Abstract. Hydrogen (H2) is being considered for many applications as an alternative to fossil fuels. Robust assessment of the climate implications of increased H2 usage in the global economy is partly hindered by uncertainties in its biogeochemical cycle. Here we use NOAA H2 dry air mole fraction observations from air samples collected from ground-based and ship platforms from 2010 to 2019 to evaluate the representation of H2 in the NOAA GFDL-AM4.1 atmospheric chemistry-climate model. We find that the model captures the observed interhemispheric gradient well but underestimates the surface concentration of H2 by about 10 ppbv. Observations show a 1–2 ppbv/year mean increase in surface H2 at background stations, while the simulated H2 exhibits no significant change over the 2010–2019 period. We show that this model bias is primarily driven by the estimated decrease of anthropogenic emissions, mostly from transportation, and that including leakage from H2-producing facilities can improve the simulated trend. We find that changes in soil moisture, soil temperature, and snow cover…

Abstract. Chemical losses of ambient reactive volatile organic compounds (VOCs) is a long-term issue yet to be resolved in VOC source apportionments. These losses substantially reduce the concentrations of highly reactive species in the apportioned factor profiles and result in the underestimation of source contributions. This review assesses the common methods and existing issues in ways to reduce losses and loss impacts in source analyses and suggest research directions for improved VOC source apportionments. Positive Matrix Factorization (PMF) is now the main VOC source analysis method compared to other mathematical models. The issue in using any apportionment tool is the processing of the data to be analyzed to reduce the impacts of reactive losses. Estimating the initial concentrations of ambient VOCs based on photochemical age has become the primary approach to reduce reactive loss effects in PMF except for selecting low reactivity species or nighttime data into the analysis. Currently, the initial concentration method only considers daytime reactions with hydroxyl (•OH)…

Abstract. Biogenic Volatile Organic Compounds (BVOCs) are emitted by vegetation and react with other compounds to form ozone and secondary organic matter (OM). In regional air-quality models, biogenic emissions are often calculated using a Plant Functional Type approach, which depends on the land-use category. However, over cities, the land-use is urban, so trees and their emissions are not represented. Here, we develop a bottom-up inventory of urban-tree biogenic emissions, in which the location of trees and their characteristics are derived from the tree database of the Paris city combined with allometric equations. Biogenic emissions are then computed for each tree based on their leaf dry biomass, tree-species dependent emission factors and activity factors representing the effects of light and temperature. Emissions are integrated in WRF-CHIMERE air-quality simulations performed over June–July 2022. Over Paris city, the urban tree emissions have a significant impact on OM, inducing an average increase of OM of about 5 %, reaching 14 % locally during the heatwaves. Ozone…

Abstract. The regulation introduced in 2020 that limits the sulfur content in shipping fuel has reduced sulfur emissions over global open oceans by about 80 %. This is expected to have reduced aerosols that both reflect solar radiation directly and affect cloud properties, with the latter also changing the solar radiation balance. Here we investigate the impacts of this regulation on aerosols and climate in the HadGEM3-GC3.1 climate model. The global aerosol effective radiative forcing caused by reduced shipping emissions is estimated to be 0.13 W m-2, which is equivalent to about 50 % of the positive forcing caused by the global reduction in all anthropogenic aerosols since late 20th century. Ensembles of global coupled simulations from 2020–2049 predict a global mean warming of 0.04 K averaged over this period. Our simulations are not clear on whether the global impact is yet to emerge or has already emerged because the present-day impact is masked by variability. Nevertheless, the impact of shipping emission reductions will have either already committed us to warming above the…

Abstract. The Geostationary Environment Monitoring Spectrometer (GEMS) onboard GEO-KOMPSAT 2B was successfully launched in February 2020 and has monitored Asia. We present the first evaluation of the operational GEMS formaldehyde (HCHO) vertical column densities (VCDs) during the in-orbit test period (IOT) (August–October 2020) and onward by comparing them with the products from Tropospheric Monitoring Instrument (TROPOMI), Fourier-Transform Infrared (FTIR), and Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) instruments. During the in-orbit test period, the GEMS HCHO VCDs reproduced the observed spatial pattern of TROPOMI VCDs over the whole domain (r=0.62) with high biases (10–16 %). In the afternoon, GEMS VCDs were too high over the west side of the tropics. We corrected this issue by adding polarization sensitivity vectors of the GEMS instrument as an additional fitting parameter in the retrieval algorithm. Using observed radiances from clear-sky pixels as the reference spectrum in the spectral fitting significantly contributed to reducing artifacts in…

Abstract. Despite significant improvements in air quality in recent years, the Sichuan Basin (SCB) is still facing frequent haze pollution in winter. In this study, the chemical components of PM2.5 in a typical pollution period at the beginning of 2023 in Chengdu, a megacity in the SCB, were characterized by bulk-chemical and single-particle analysis, and the PM2.5 sources and formation mechanism of pollution were analyzed. The average mass concentration of PM2.5 during the study period was 95.4±29.7 μg m-3. Organic matter (OM) was the most abundant component (35.3 %), followed by nitrate (22.0 %), sulfate (9.2 %) and ammonium (7.8 %). The aerosol particles were classified into five categories: mineral, OM, S-rich, soot and fly ash/metal particles, and most of them were in the state of internal mixing. The entire observation period could be divided into two non-pollution periods (NP-1 and NP-2) and two haze periods (Haze-1 and Haze-2). With the evolution of pollution, the bulk-chemical and single-particle analysis exhibited similar characteristics, suggesting that Haze-1 was mainly…

Abstract. The added heat in cities amplifies the health risks of heat waves. At night under calm winds and cloud free skies, the air in the urban canopy layer can be several degrees warmer than in rural areas. This lower nocturnal cooling in the built-up settings poses severe health risks to the urban inhabitants as indoor spaces cannot be ventilated effectively. With heat waves becoming more frequent and more intense in future climates, many cities are expanding their green spaces with the aim to introduce cooling through shading, evaporation, and lower heat storage capacities. In this study, it is assessed how the evening and night-time cooling effect of urban parks (relative to near-by built-up settings) varies with the park size and the meso-scale atmospheric conditions during warm summer periods. Using a combination of meteorological surface station data and compact radiosondes, the cooling effect is quantified for several urban parks (about 15 ha) and urban woods (about 900 ha). A profiling Doppler wind lidar deployed in the city centre is used to measure turbulent vertical…

Abstract. Methane (CH4) is an important anthropogenic greenhouse gas and its rising concentration in the atmosphere contributes significantly to global warming. A comparatively small number of highly emitting persistent methane sources is responsible for a large share of global methane emissions. The identification and quantification of these sources, which often show large uncertainties regarding their emissions or locations, is important to support mitigating climate change. The TROPOspheric Monitoring Instrument (TROPOMI) onboard on the Sentinel-5 Precursor (S5P) satellite, launched in October 2017, provides measurements of the column-averaged dry-air mole fraction of atmospheric methane (XCH4) with a daily global coverage and a high spatial resolution of up to km2, enabling the detection and quantification of localized methane sources. We developed a fully automated algorithm to detect regions with persistent methane enhancement and to quantify their emissions using a monthly TROPOMI XCH4 dataset from the years 2018–2021. We detect 217 potential persistent source regions…

Abstract. Globally emissions from aviation affect the Earth’s climate via a complex set of processes. Contrail cirrus and carbon dioxide emissions are the largest factors from aviation in the radiative forcing on climate. Although contrail cirrus enhances the impact of natural clouds on the climate, there are still unresolved questions concerning their characteristics and life cycle. Despite extensive research in studying contrails, significant uncertainties persist. Contrail cirrus encompasses linear contrails and the associated cirrus clouds; these are characterized by ice particle properties, e.g., size, concentration, extinction, ice water content, optical depth, geometrical depth, and cloud coverage. The climate impact of contrails may intensify due to projected increases in air traffic. The radiative forcing from global contrail cirrus has the potential to triple and could reach as much as 160 mW m−2 by 2050. This projection is based on anticipated growth in air traffic and a potential shift to higher altitudes. The future climate impact of contrail cirrus is influenced by…

Abstract. The anthropogenic and biogenic contributions of isoprene, monoterpenes, sesquiterpenes and methanol in an urban area were estimated based on direct eddy covariance flux observations during four campaigns between 2018 and 2021. While these compounds are typically thought to be dominated by biogenic sources on regional and global scales, the role of potentially significant anthropogenic emissions in urban areas has been recently debated. Typical fluxes of isoprene, monoterpenes and sesquiterpenes were on the order of 0.09 nmol m−2 s−1, 0.09 nmol m−2 s−1 and 0.003 nmol m−2 s−1 during spring. During summer, emission fluxes of isoprene, monoterpenes and sesquiterpenes were higher on the order of 0.85 nmol m−2 s−1, 0.11 nmol m−2 s−1, 0.004 nmol m−2 s−1. It was found that the contribution of the anthropogenic part is strongly seasonally dependent. For isoprene the anthropogenic fraction can be as high as 64 % in spring, but is typically very low < 18 % during the summer season. For monoterpenes the anthropogenic fraction was estimated between 43 % in spring and less than 20 % in…

Abstract. The emergence of aerosol reanalyses in recent years has facilitated a comprehensive and systematic evaluation of Aerosol Optical Depth (AOD) trends and attribution over multi-decadal timescales. Notable aerosol reanalyses currently available include NAAPS-RA from the U.S. Naval Research Laboratory; the NASA MERRA-2; JRAero from the Japan Meteorological Agency (JMA); and CAMSRA from Copernicus/ECMWF. These aerosol reanalyses are based on differing underlying meteorology models, representations of aerosol processes, and data assimilation methods and treatment of AOD observations. This study presents the basic verification characteristics of these four reanalyses versus both AERONET and MODIS retrievals in monthly AOD properties and identifies the strength of each reanalysis and the regions where diversity and challenges are prominent. Regions with high pollution and often mixed fine-coarse mode aerosol environments such as South Asia, East Asia, Southeast Asia, and the Maritime Continent pose significant challenges, as indicated by higher monthly AOD root mean square error.…

Abstract. Narrowing surface ozone disparities between urban and nonurban areas escalate health risks in densely populated urban zones. A comprehensive understanding of the impact of ozone photochemistry processes on this transition remains constrained by our knowledge of aerosol effects and the spatial availability of surface monitoring. Here we developed a novel deep learning framework, which could perceive spatiotemporal dynamics from adjacent grids by multidimensional self-attention operation, integrating multi-sources data to estimate daily 500 m surface ozone, nitrogen dioxide (NO2) and fine particulate matter (PM2.5) concentrations. Subsequently, three distinct ozone formation regimes linked with its precursors, aerosols, and meteorology were delineated through an interpretable machine learning method. The evaluations of the framework exhibited average out-of-sample cross-validation coefficient of determination of 0.96, 0.92 and 0.95 for ozone, NO2 and PM2.5, respectively. In 2020, urban ozone levels in Shandong surpassed those in nonurban due to a more pronounced decrease in…

Abstract. While the growth rate of atmospheric CO2 mole fractions can be measured with high accuracy, there are still large uncertainties in the attribution of this growth to diverse anthropogenic and natural sources and sinks. One major source of uncertainty is the net flux of carbon dioxide from the biosphere to the atmosphere, the Net Ecosystem Exchange (NEE). There are two major approaches to quantifying NEE: top-down approaches that typically use atmospheric inversions, and bottom-up estimates which rely on process-based or data-driven terrestrial biosphere models or inventories. Both approaches have known limitations. Atmospheric inversions produce estimates of NEE that are consistent with the atmospheric CO2 growth rate at regional and global scales, but are highly uncertain at smaller scales. Bottom-up data-driven flux models match local observations of NEE, but have difficulty in accurately upscaling to a global estimate. We combine the two approaches, constraining a bottom-up data-driven flux model trained on meteorological, remotely-sensed, and eddy-covariance data with…

Abstract. Recent years have seen an increase in the use of wood for energy production of over 30 %, and this trend is expected to continue due to the current energy crisis and geopolitical instability. At present, residential wood burning (RWB) is one of the most important sources of organic aerosols (OA) and black carbon (BC). While BC is recognized for its large light absorption cross-section, the role of OA in light absorption is still under evaluation due to their heterogeneous composition and source-dependent optical properties. Studies that characterize wood-burning aerosol emissions in Europe typically focus on urban and background sites and only cover BC properties. However, RWB is more prevalent in rural areas, and the present scenario indicates that an improved understanding of the RWB aerosol optical properties and their subsequent connection to climate impacts is necessary for rural areas. We have characterized atmospheric aerosol particles from a central European rural site during wintertime in the village of Retje in Loški Potok, Slovenia, from 01.12.2017 to…

Abstract. We investigate the causes of the renewed growth of atmospheric methane (CH4) mole fractions after 2007 by using variational inverse modelling with a three-dimensional chemistry-transport model. Together with CH4 mole fraction data, we use the additional information provided by observations of CH4 isotopic com-positions (in 13C:12C and in D:H) to better differentiate between the emission categories compared to as-similating CH4 mole fractions alone. Our system allows us to optimize either the CH4 emissions only or both the emissions and the source isotopic signatures (δsource(13C, CH4) and δsource(D, CH4)) of five emission categories. Consequently, we also assess here for the first time the influence of applying random errors to both emissions and source signatures in an inversion framework. As the computational cost of a single in-version is extremely high at present, the methodology applied to prescribe source signature uncertainties is simple so that it serves as a basis for future work. When random uncertainties in source isotopic signatures are accounted for, our…