Governments and industries worldwide are seeking methods to accurately estimate their methane inventories, particularly in the open-cut coal mining sector, where quantifying facility-level emissions remains challenging and robust verification methods are not yet widespread. Here, we compare methane emission rates estimated from two aircraft-based measurement platforms with operator-reported emissions from an open-cut coal mine in the Bowen Basin (Queensland, Australia). Coarse-resolution satellite-based data identified the mine as a significant emitter, making it ideal for case studies using airborne in situ and remote sensing platforms that provide high-resolution measurements to isolate mine-scale emissions. Using airborne in situ measurements, we estimated methane emission rates of 14.0 +/- 3.3 (+/- 2 sigma) t h-1 during May and June 2022. In September 2023, airborne in situ and remote sensing measurements yielded consistent emission rate estimates of 9.6 +/- 1.9 (+/- 2 sigma) t h-1 and 11.3 +/- 5.3 (+/- 2 sigma) t h-1, respectively. If sustained, these rates would equate to annual emissions of 1.5-4.2 Mt of CO2 equivalents (CO2-e) year-1, 3-8 times higher than operator-reported annual Scope 1 emissions (0.53-0.54 Mt of CO2-e year-1). Beyond highlighting the potential for under-reporting of emissions at this mine, our results indicate that aircraft-based technologies are valuable tools for supporting accurate reporting of facility-scale methane emissions from open-cut coal mines.

Regional scale marine cloud brightening (MCB) has been proposed as a novel climate intervention to reduce the impact of global warming and associated marine heatwaves on the Great Barrier Reef. The concept relies on artificially generated sea spray aerosols (SSA) at the ocean surface and their transport in sufficient quantities to low-level maritime clouds. A portion of the SSA that reaches cloud height can act as additional cloud condensation nuclei and modify cloud microphysical properties, potentially reducing the amount of solar radiation reaching the sea surface. Although modelling data supports the MCB concept, field experiments demonstrating the dispersion of artificially produced SSA to clouds have not been previously reported. Here, we show that within a field of low-level trade wind cumulus-type clouds, an aerosol plume generated at the sea surface on board a research vessel was rapidly advected to cloud base height. Aircraft measurements conducted during two different sampling strategies, detected the aerosol plume from the vessel’s sea water atomisation system just below cloud bases at 700–900 m altitudes. For an estimated surface level aerosol production rate of 4 × 10 ^14 s ^−1 , aerosol concentrations at cloud base were detected with peak number concentrations of up to ∼1 × 10 ^3 cm ^−3 . Although such production rates of aerosol particles are orders of magnitude less than what is envisioned for any practical implementation of MCB, our results indicate that cloud perturbation experiments should now be possible using surface-produced SSA.

In recent years, credible atmospheric observations of methane emissions suggest that annual methane emission estimates in inventories for some Australian coal mining regions or facilities may be underestimated. A lack of well-constrained, mine-scale studies for open-cut (pit) coal mines continues to hinder discussions on emission estimates and the refinement of estimation methods for Australian open-cut coal mining facilities. Here, we present preliminary results from aircraft- and ground-based atmospheric measurements recorded in November 2024 in the Hunter Coalfield, NSW, Australia.Australia employs higher-Tier IPCC methodologies – Tier 2 (basin-specific) and Tier 3 (mine-specific, Methods 2 and 3 ) – under its National Greenhouse and Energy Reporting (NGER) Scheme to estimate open-cut coal mine emissions. These methods rely on the use of coal core gas content to estimate methane emissions from open-cut mine complexes. However, Methods 2 and 3 have never been validated using airborne or ground-based time series observations.While coarse-resolution satellites like TROPOMI can quantify coal mine emissions at regional scales (Sadavarte et al., 2021; Palmer et al., 2021), their limited spatial resolution reduces their effectiveness for verifying annual inventory reported emissions at the scale of individual mines. Additionally, the ability of point-source imaging satellites to quantify emissions from individual open-cut coal mines remains uncertain. Coal seam blasting prior to extraction can be considered a point source; however, open-cut coal mines have various continuous diffuse methane sources that also need to be quantified. The diffuse sources include, among others, emissions from beneath the pit floor, lateral diffusion along coal seams and other rock strata in the mine walls, rock waste piles, and areas of in situ biological production, such as water management ponds. Aircraft- and ground-based technologies have the potential to measure both point and diffuse sources of methane, thus providing a potential pathway for verifying greenhouse gas inventories determined using approved IPCC methodologies.During this measurement campaign in the Hunter Coalfield, a research aircraft flew instruments to collect in-situ atmospheric measurements of methane and carbon dioxide mole fractions, along with GPS and meteorological data. These data were used to make rate of methane emission estimates downwind of individual coal mine complexes. Aerosol size and particle number concentration measurements and high-resolution airborne LiDAR imagery were also acquired to aid in source attribution. These measurements were complemented by ground-based EM27/SUN solar absorption spectrometer instruments positioned upwind and downwind of the same coal mining complexes. Comparisons between emissions derived from the aircraft-base, ground station EM27/SUN observations, and operator-reported coal mine methane emissions will be presented.Palmer, P. I., Feng, L., Lunt, M. F., Parker, R. J., Bösch, H., Lan, X., Lorente, A., and Borsdorff, T.: The added value of satellite observations of methane for understanding the contemporary methane budget, Phil. Trans. R. Soc. A., 379, 20210106, https://doi.org/10.1098/rsta.2021.0106, 2021.Sadavarte, P., Pandey, S., Maasakkers, J. D., Lorente, A., Borsdorff, T., van der Gon, H. D., Houweling, S., and Aben, I.: Methane emissions from superemitting coal mines in Australia quantified using TROPOMI satellite observations, Environmental Science & Technology, 55, 16573–16580, https://doi.org/10.1021/acs.est.1c03976, 2021.

Current extremes within regional water cycles, extensive drought periods and torrential flooding, are associated in literature and media to first indicators of greenhouse gas driven climate change. Indeed, they are among major threats to be expected from climate change model results. The main obvious physical process behind such global warming water cycle extremes, is the temperature dependent water vapor content of air (Clausius Clapeyron, 1834, CC) and it’s increase by ~ 7% per degree C. Naturally the water vapor input into the atmosphere via evapotranspiration is dependent on shortwave radiation reaching the surface, a process controlled partially by fine particles, partially by clouds. Here the ultrafine, invisible, fraction of the aerosols is becoming important.Ultrafine particles (UFP) acting as cloud condensation nuclei (CCN) are the driving force behind cloud modification and changing rainfall patterns. However, the sources and budgets of anthropogenic primary and secondary particles were not well known. Based on airborne measurements we identified as a major contribution modern fossil fuel flue gas cleaning techniques to cause a doubling of global primary UFP number emissions. The subsequent enhancement of CCN numbers has several side effects. It’s changing the size of the cloud droplets and delays raindrop formation, suppressing certain types of rainfall and increasing the residence time of water vapor in the atmosphere. This additional latent energy reservoir is directly available for invigoration of rainfall extremes. Additionally it’s a further contribution to the column density of water vapor as a greenhouse gas and important for the infrared radiation budget. The localized but ubiquitous fossil fuel related UFP emissions and their role in the hydrological cycle, may thus contribute to regional or continental climate trends, such as increasing drought and flooding, observed within recent decades.We discuss the impact of the ultrafine fraction on the hydrological cycle and its historical timeline. Ultrafine particles (UFP) initially don’t interact with radiation like fine ones. However, a significant increase of the ultrafine particle burden may serve similar to CC to more water vapor molecules, respectively more latent energy in the troposphere, especially in the altitude range of convective clouds. We also discuss the origin of the majority of UFP, whether a simple dependence of ultrafine particles on the atmospheric sulphur load is a reasonable and valid assumption and what should be taken additionally into account for future UFP szenarios.Junkermann, W. & Hacker, J., 2022, Unprecedented levels of ultrafine particles, major sources, and the hydrological cycle, Nature Scientific Reports, 12:7410 https://doi.org/10.1038/s41598-022-11500-5Junkermann, W. (2022). Ultrafine particle emissions in the Mediterranean region. In F. Dulac, S. Sauvage, & E. Hamonou (Eds.), Atmospheric chemistry in the Mediterranean region (Vol. 2, From air pollutant sources to impacts). Springer, 21 pp. https://doi.org/10.5445/IR/1000154173

Methane (CH4) is the second most important anthropogenic greenhouse gas (GHG), and its emissions reduction has been identified as an essential mitigation target to slow down climate change. According to inventories, fossil fuel production and usage account for roughly 17% of the global CH4 emissions, of which approximately 33% originate from coal mining. Accurate identification of coal mining-related CH4 sources and quantification of their annual emission rate is needed for corporate reporting requirements, national inventory verification, and the development of CH4 mitigation strategies.A previous study estimated CH4 emissions for six coal mines in the Bowen Basin in Queensland, Australia, using TROPOMI satellite measurements. It covered a sub-area of the Bowen Basin, where coal is mined at over 40 active mining locations distributed over 60,000 km2. The study showed a significant discrepancy compared to inventory estimates by a factor of 7 during 2018 and 2019.To further verify satellite estimates and improve knowledge of the distribution, persistence, and strength of emissions of this mining region, the Bowen Basin CH4 Mapping (BBCMap) Campaign was conducted in September-October 2023, funded by and performed in collaboration with UNEP's International Methane Emissions Observatory. During this campaign, two HK36 Eco-Dimona research aircraft carrying complementary sensing instrumentation were deployed. The MAMAP2D-Light (Methane Airborne MAPper 2D – Light) imaging spectrometer for estimating atmospheric CH4 and CO2 column anomalies and a lidar for topography scans were deployed on one DIMONA HK36 research aircraft, while the second identical aircraft was equipped with an in-situ payload consisting of an LGR OA-ICOS gas analyser for simultaneous measurements of atmospheric CH4, CO2, and water vapor concentrations, a turbulence probe for wind statistics, and a bag sampler for collecting multiple gas samples during each flight for later 13C isotope analyses in the laboratory. This two-aircraft strategy allowed coordinated measurements of CH4 emissions from different coal mines with both remote sensing and in-situ instruments and simultaneous wind measurements, which is essential for deriving a robust flux estimate.During the campaign, 39 flights were conducted, covering approximately 33 mines across roughly 20,000 km2, focussing on the northern part of the Bowen Basin. Preliminary MAMAP2D-Light measurements of atmospheric CH4 column anomalies and emission estimates for both open-cut and underground coal mines will be presented and discussed.

Ultrafine particles (UFP) acting as cloud condensation nuclei (CCN) are the driving force behind changing rainfall patterns. Recently observed weather extremes like floods and drought might be due to changing anthropogenic UFP emissions. However, the sources and budgets of anthropogenic primary and secondary particles are not well known. Based on airborne measurements we identified as a major contribution modern fossil fuel flue gas cleaning techniques to cause a doubling of global primary UFP number emissions. The subsequent enhancement of CCN numbers has several side effects. It's changing the size of the cloud droplets and delays raindrop formation, suppressing certain types of rainfall and increasing the residence time of water vapour in the atmosphere. This additional latent energy reservoir is directly available for invigoration of rainfall extremes. Additionally it's a further contribution to the column density of water vapour as a greenhouse gas and important for the infrared radiation budget. The localized but ubiquitous fossil fuel related UFP emissions and their role in the hydrological cycle, may thus contribute to regional or continental climate trends, such as increasing drought and flooding, observed within recent decades.

Continental as well as maritime ultrafine particles as cloud condensation nuclei (CCN) are likely initially produced by gas to particle conversion starting with nucleation mode aerosol and slowly (within several hours) growing into CCN sizes. Although these birth and growing processes were well investigated since about 50 years, the source locations, where the anthropogenic fraction of these particles are preferably formed still remain uncertain as well as the strength of individual natural or anthropogenic sources.We present an analysis based on two decades of airborne studies of number and size distribution measurements across Europe, Australia, Mexico and China on nucleation and Aitken mode particles serving as CCN or their precursors. Selected flight patterns allow source apportionment for typical major sources and even a quantitative estimate of their emission rates.Contrary to current global climate model RCP assumptions with decreasing aerosol from 2005 towards the end of the century trends of ultrafine particles and CCN are no longer correlated to sulphur emissions within the last two decades. Nowadays nitrogen and ammonia chemistry is becoming increasingly important for global anthropogenic nanoparticle particle formation and number concentrations. Due to their impact on the hydrological cycle, changes like a slowdown of raindrop production, an increased latent heat flux into the lower free troposphere, an invigoration of torrential rains and a larger water vapour column density might be the consequences. Such recently observed weather patterns are well in agreement with current observations of regional UFP/CCN concentrations and their timely evolution.

The manuscript describes aircraft based vertical profiles of nanometer sized particles in the range from 1.5 to 400 nm with a main emphasis on the lower particles sizes of 1.5 to 3 nm and 3-20 nm.The authors summarize data from 7 years of flight experiments and conclude that a larger fraction of ground based nanoparticle events (NPE's) (> 40% of observations) occurs in cases when small particles are transported downwards from the residual layer into the planetary boundary layer.A case study is shown as well for one day in May, 2017 to explain the interpretations.A schematic drawing of the proposed processes is included.

A small light-weight in-house made miniature chilled-mirror hygrometer (CMH) for fixed wing UAS (unmanned aircraft system) is presented, with its features and limitations. Therefore, first measurements of the CMH equipped on the small research UAS of type MASC-3 (multi-purpose airborne sensor carrier) operated by the University of Tübingen are shown. A comparison against a very accurate state of the art capacitive industrial humidity sensor (SHT31) is done. The sensor consists of a TEC (thermoelectric cooler) covered by a gold mirror. The TEC is controlled by a commercially available microprocessor with an on-board PID (proportional-integral-derivative) controller. The results of the CMH measurements are in good agreement with the industrial-made capacitive sensor. The absolute accuracy of the measured dew point temperature by the CMH is in the range of ±0.2 K. Spectra show evidence that the CMH is capable to measure turbulent humidity fluctuations in the atmosphere with a temporal resolution of up to 10 Hz. Such a fast humidity sensor aboard a small UAS has the potential to study humidity fluxes in the surface layer over complex terrain, behind wind energy converters and humidity variations over land and sea surfaces in general.

The paper provides an overview of an airborne measurement campaign with a microlight aircraft over the Pokhara Valley region, Nepal, a metropolitan region in the central Himalayan foothills. This is the first aerial measurement in the central Himalayan foothill region, one of the polluted but relatively poorly sampled regions of the world. Conducted in two phases (in May 2016 and December 2016–January 2017), the goal of the overall campaign was to quantify the vertical distribution of aerosols over a polluted mountain valley in the Himalayan foothills, as well as to investigate the extent of regional transport of emissions into the Himalayas. This paper summarizes results from the first phase where test flights were conducted in May 2016 (pre-monsoon), with the objective of demonstrating the potential of airborne measurements in the region using a portable instrument package (size with housing case: 0.45 m × 0.25 m × 0.25 m, 15 kg) onboard an ultralight aircraft (IKARUS-C42). A total of five sampling test flights were conducted (each lasting for 1–1.5 h) in the Pokhara Valley to characterize vertical profiles of aerosol properties such as aerosol number and size distribution (0.3–2 µm), total particle concentration (>14 nm), aerosol absorption (370–950 nm), black carbon (BC), and meteorological variables. Although some interesting observations were made during the test flight, the study is limited to a few days (and only a few hours of flight in total) and thus the analysis presented may not represent the entire pollution–meteorology interaction found in the Pokhara Valley. The vertical profiles of aerosol species showed decreasing concentrations with altitude (815 to 4500 m a.s.l.); a steep concentration gradient below 2000 m a.s.l. in the morning; and mixed profiles (up to ca. 4000 m a.s.l.) in the afternoon. The near-surface (<1000 m a.s.l.) BC concentrations observed in the Pokhara Valley were much lower than pre-monsoon BC concentrations in the Kathmandu Valley, and similar in range to Indo-Gangetic Plain (IGP) sites such as Kanpur in India. The sampling test flight also detected an elevated polluted aerosol layer (around 3000 m a.s.l.) over the Pokhara Valley, which could be associated with the regional transport. The total aerosol and black carbon concentration in the polluted layer was comparable with the near-surface values. The elevated polluted layer was also characterized by a high aerosol extinction coefficient (at 550 nm) and was identified as smoke and a polluted dust layer. The observed shift in the westerlies (at 20–30∘ N) entering Nepal during the test flight period could be an important factor for the presence of elevated polluted layers in the Pokhara Valley.

Mountainous areas require appropriate measurement strategies to cover the full spectrum of details concerning the energy exchange at the Earth’s surface and to capture the spatiotemporal distribution of atmospheric dynamic and thermodynamic fields over them. This includes the range from turbulence to mesoscale processes and its interaction. The surface energy balance needs appropriate measurement strategies as well. In this paper, we present an overview of important experiments performed over mountainous terrain and summarize the available techniques for flow and energy measurements in complex terrain. The description includes ground-based and airborne in situ observations as well as ground-based and airborne remote sensing (passive and active) observations. Emphasis is placed on systems which retrieve spatiotemporal information on mesoscale and smaller scales, fitting mountainous terrain research needs. Finally, we conclude with a short list summarizing challenges and gaps one faces when dealing with measurements over complex terrain.

AbstractUltrafine particles (UFPs) are distributed highly unevenly in the lower troposphere. Although these UFPs are positively detectable and have been studied for more than a century, their three-dimensional distribution, formation, and budget in the atmosphere remain largely uncertain, despite their obvious climate relevance. This is due to their short lifetime and the fact that they are invisible to the human eye and to remote sensing techniques. From the moment of their emission or generation, their spatial distribution is a result of meteorological processes, regional-scale transport, local thermal convection, and rapid loss by interaction with clouds as cloud condensation nuclei. Here, we report about three-dimensional airborne in situ studies aimed at investigating UFP sources, distribution, and behavior on different spatial and temporal scales. We identified fossil fuel–burning power stations, refineries, and smelters as major anthropogenic UFP sources. On a regional scale, their emissions are significantly higher than urban emissions. Particle emissions from such power stations are released typically at altitudes between 200 and 300 m AGL. Detailed in situ measurements of particle concentration and related parameters, together with meteorological measurements and analyses, enable reliable source attribution even over several hundred kilometers downwind from the emitter. Comprehensive meteorological analysis is required to understand the highly variable 3D concentration patterns generated by advective transport and thermal convection. Knowledge of primary emission strength, together with size distributions and atmospheric 3D transport of UFPs derived from airborne measurements, makes it possible to estimate the aerosols’ impact on meteorology, hydrological cycles, and climate.

This paper present first ever vertically distributed aircraft measurements of atmospheric aerosols over Pokhara Valley in Nepal. The Himalayan region is generally polluted but only few detailed measurements of the pollution exists. Nepal, being situated in Central Himalayas, is a desirable region for conducting such measurements, in order to understand the sources and transport or aerosols in the region. Therefore, the manuscript is of definite value and well suited for ACP. The measurements seem to be well conducted, and complemented with appropriate data from ground based AODmeasurements as well as satellite and model results. There are few issues with the

Continuous measurements between July 2012 and December 2015 at the Henties Bay Aerosol Observatory (HBAO; 22∘ S, 14∘05′ E), Namibia, show that, during the austral wintertime, transport of light-absorbing black carbon aerosols occurs at low level into the marine boundary layer. The average of daily concentrations of equivalent black carbon (eBC) over the whole sampling period is 53 (±55) ng m−3. Peak values above 200 ng m−3 and up to 800 ng m−3 occur seasonally from May to August, ahead of the dry season peak of biomass burning in southern Africa (August to October). Analysis of 3-day air mass back-trajectories show that air masses from the South Atlantic Ocean south of Henties Bay are generally cleaner than air having originated over the ocean north of Henties Bay, influenced by the outflow of the major biomass burning plume, and from the continent, where wildfires occur. Additional episodic peak concentrations, even for oceanic transport, indicate that pollution from distant sources in South Africa and maritime traffic along the Atlantic ship tracks could be important. While we expect the direct radiative effect to be negligible, the indirect effect on the microphysical properties of the stratocumulus clouds and the deposition to the ocean could be significant and deserve further investigation, specifically ahead of the dry season.

U ltrafine particles (UFPs) in the atmosphere (diameter <100 nm) have a major impact on the environment through a wide variety of processes. They provide reaction surfaces for heterogeneous chemical processes in the atmosphere or can act as cloud condensation nuclei (CCN). While fine particles (>100 nm) interact directly with shortwave radiation, UFPs do not. Yet UFPs affect shortand longwave radiation indirectly, by way of their interactions with cloud microphysics. Once UFPs reach sizes larger than 40 nm, they effectively contribute to CCN (Twomey 1977; Andreae 2009; Ma et al. 2016), which then can enhance the number of cloud droplets at the expense of cloud droplet size (Rosenfeld et al. 2008; Leaitch et al. 2010; Junkermann et al. 2009). Subsequent changes in cloud brightness and lifetime are well established (Twomey 1974; Albrecht 1989). These effects have even been proposed as a potentially exploitable physical process for geoengineering (Latham et al. 2008). Yet the concurrent reduction of cloud droplet size modes may have unwanted side effects, such as changes of the distribution and intensity of rainfall on a larger scale (Rosenfeld 2000; Teller and Levin 2006; Teller et al. 2012; Junkermann et al. 2011b; Fan et al. 2018) that, in turn, affects the hydrological cycle (Bister and Kulmala 2011; Riuttanen et al. 2016). Techniques for the detection of UFPs, condensation particle counters (CPC), were developed more than a hundred years ago by Coulier (1875) and Aitken (1889). Since then, UFPs have been measured in polluted urban and industrial environments, as well as in remote locations. For a historic review, see Mohnen and Hidy (2010). For airborne applications, Bigg and Turvey (1978) and Ayers et al. (1979) This article is licensed under a Creative Commons Attribution 4.0 license. AFFILIATIONS: Junkermann—Karlsruhe Institute of Technology, Institute of Meteorology and Climate Research, GarmischPartenkirchen, Germany, and Flinders University, Adelaide, South Australia, Australia; Hacker—Airborne Research Australia, Parafield Airport, and Flinders University, Adelaide, South Australia CORRESPONDING AUTHOR: Wolfgang Junkermann, wolfgang. junkermann@kit.edu