Energy, transport, urbanization and burning are responsible for changes in atmospheric BC. This work uses direct solar atmospheric column measurements of single scatter albedo [SSA] retrieved at multiple wavelengths from AERONET at 68 Asian sites over 17 years. A MIE model is solved across the wavelengths using a core-shell mixing approximation to invert the probabilistic BC, shell size, and UV SSA. Orthogonal patterns are obtained for urban, biomass burning [BB], and long-range transport [LRT] conditions, which are used to analyze and attribute source types of BC across the region. Large urban areas (thought to be dominated by urban BC) are observations during targeted times (shorter than seasonally) to yield significant contributions from non-urban BC. BB and LRT are observed to dominate Beijing and Hong Kong 2 months a year. LRT is observed during the clean Asian Monsoon season in both Nepal and Hong Kong, with sources identified from thousands of kilometers away. Computing the shift in shell size required to constrain the results approximates secondary aerosol growth in-situ, and subsequently aerosol lifetime, which is found to range from 11 days to a month, implying both a significant amount of BC above the boundary layer, and that BC generally has a longer lifetime than PM2.5. These findings are outside of the range of most modeling studies focusing on PM2.5, but are consistent with independent measurements from SP2 and modeling studies of BC that use core-shell mixing together with high BC emissions.
Lower atmosphere variations in the martian water vapour and hydrogen abundance during the Mars Year (MY) 34 C storm from LS=326.1◦-333.5◦ and their associated effect on hydrogen escape are investigated using a multi-spacecraft assimilation of atmospheric retrievals into a Martian global circulation model. Elevation of the hygropause and associated increase in middle atmosphere hydrogen at the peak of the MY 34 C storm led to a hydrogen escape rate of around 1.4×109 cm−2s−1 , meaning the MY 34 C storm enhanced water loss rates on Mars to levels observed during global-scale dust storms. The water loss rate during the MY 34 C storm (a loss of 15% of the total annual water loss during only 5% of the year) was three times stronger than the weak MY 30 C storm assimilation, demonstrating that interannual variations in C storm strength must be considered when calculating the integrated loss of water on Mars.
Quantification of the magnitude and long-term changes of ozone concentrations transported into the US is important for effective air quality policy development. We synthesize multiple published trend analyses of western US baseline ozone, and show that all results are consistent with an overall, non-linear change – rapid increase during the 1980s that slowed in the 1990s, maximized in the mid-2000s, and was followed by a slow decrease thereafter. This non-linear change accounts for ~2/3 of the variance in the published linear trend analyses; we attribute the other 1/3 to unquantified autocorrelation in the analyzed data sets. Recent systematic changes in baseline ozone at the US West Coast have been relatively small - the standard deviation of the 2-year means over the 1990-2017 period is 1.5 ppb. International efforts to reduce anthropogenic precursor emissions from all northern mid-latitude sources could possibly reduce baseline ozone concentrations, thereby improving US ozone air quality.
Current changes in tropical South America due to atmospheric warming, deforestation, and glacier retreat impact moisture and water exchange between the Amazon basin and the Andes. Thus, a deeper understanding of past atmospheric variability is crucial for developing strategies for climate and environmental change scenarios in this region. Within this context, we investigated an 18-year firn core drilled at the Illimani to interpret its aerosol composition (trace elements and major ions) in relation to seasonal processes, particularly atmospheric circulation over the Amazon basin. The resulting 21st-century record showed reduced Cr contamination over the Altiplano in comparison to the late 20th century, which was probably related to reduced emissions from mining activities. Sulfur records suggest the influence of volcanic eruptions in 2006 (Rabaul) and 2014 (Nyamuragira-Nyiragongo). Overall, the aerosol composition was mainly modulated by precipitation variability over the Altiplano at both annual and seasonal timescales. However, Mn was enriched due to strengthened low-level jets in the Amazon basin during the dry season, especially in 2015. This was corroborated by the reanalysis data. Furthermore, Mn, Co, and Fe showed an unprecedented peak in the record during the wet season of 2014, which was consistent with the arrival of a dust plume from Africa over Amazonia. Therefore, the Mn enrichment record can be used as a new proxy for obtaining information about the South American Low-Level Jet, and, when considered together with more elements, might also indicate snow layers that were possibly loaded with aerosols from Africa.
The Global Burden of Disease attributes millions of premature deaths to ambient air pollution each year, making it one of the largest environmental health risks faced by society. This mortality is largely due to exposure to fine particulate matter (PM2.5). In the United States, the Environmental Protection Agency estimated that 50.5 million people lived in counties with PM2.5 concentrations above the level of the National Ambient Air Quality Standards in 2020. PM2.5 levels can be derived from satellite aerosol optical depth (AOD) measurements providing comprehensive spatial and temporal coverage. However, the chemical composition of PM2.5 affects the mechanisms by which adverse health effects occur, and thus there is a pressing need for linking satellite data with high-resolution atmospheric modeling of PM2.5 composition. In order to better inform public health policy and decision-making, we aim to estimate near-real-time (NRT) surface PM2.5 composition informed by satellite AOD measurements and chemical transport modeling for the first time. Here, we demonstrate this framework for hindcast estimates in year 2021. NRT AOD is collected from multi-source remote sensing data including Moderate Resolution Imaging Spectroradiometer (MODIS; Aqua and Terra), the Visible Infrared Imaging Radiometer Suite (VIIRS; Dark Target and Deep Blue), and Multi-Angle Imaging SpectroRadiometer (MISR). The data obtained from these products are combined into daily, 10-km AOD estimates and used to scale simulated total PM2.5. GEOS-Chem (v13.1.2) nested regional simulations are run over North America with GEOS-Forward Processing (FP) assimilated meteorology at resolution 0.25° lat. x0.3125° lon. (approximately 20-30km) to simulate daily AOD and get an initial estimate of PM2.5 composition. This estimate is interpolated into the 10-km grid and multiplied with the satellite-adjusted total PM2.5 composition to produce concentrations of each PM2.5 species. This satellite-constrained chemical transport model framework estimates of PM2.5 will ultimately be evaluated against observations and compared to estimates using standard satellite products to inform future use of this framework to predict ambient air pollution health risks in true near-real-time.
In situ measurements of ionospheric and thermospheric temperatures are experimentally challenging because orbiting spacecraft typically travel supersonically with respect to the cold gas and plasma. We present O2+ temperatures in Mars’ ionosphere derived from data measured by the SupraThermal And Thermal Ion Composition (STATIC) instrument onboard the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft. We focus on data obtained during nine special orbit maneuvers known as Deep Dips, during which MAVEN lowered its periapsis altitude from the nominal 150 km to 120 km for one week in order to sample the ionospheric main peak and approach the homopause. We use two independent techniques to calculate ion temperatures from the measured energy and angular widths of the supersonic ram ion beam. After correcting for background and instrument response, we are able to measure ion temperatures as low as 100 K with associated uncertainties as low as 10%. It is theoretically expected that ion and electron temperatures will converge to the neutral temperature at altitudes below the exobase region (~180-200 km) due to strong collisional coupling; however, no evidence of the expected thermalization is observed. We have eliminated several possible explanations for the observed temperature difference between ions and neutrals, including Coulomb collisions with electrons, Joule heating, and heating caused by interactions with the spacecraft. Our current study leaves one plausible heating mechanism, the release of internal energy from O2+ that becomes vibrationally excited as a result of atmospheric chemistry, but future work is needed to assess its validity.
In the last decade, much work has been done to better understand methane (CH4) emissions from the oil and gas (O&G) industry in the United States. Ethane (C2H6), a gas that is co-emitted with thermogenic sources of CH4 , is emitted in the US almost entirely by the O&G sector. In this study, we perform an inverse analysis on 300 hours of atmospheric boundary layer C2H6 measurements to estimate C2H6 emissions from the US O&G sector. Measurements were collected from 2017-2019 as part of the Atmospheric Carbon and Transport (ACT) America aircraft campaign and encompass much of the central and eastern United States. We find that for the fall, winter, and spring campaigns, C2H6 data consistently exceeds values that would be expected based on EPA O&G leak rate estimates. C2H6 observations from the summer 2019 dataset show significantly lower C2H6 enhancements in the southcentral region that cannot be reconciled with data from the other three seasons, either due to complex meteorological conditions or a temporal shift in the emissions. Converting the fall, winter, and spring season posterior C2H6 emissions estimate to an inventory of O&G CH4 emissions, we estimate that O&G CH4 emissions are larger than EPA inventory values by more than 50%. Uncertainties in the gas composition data limit the effectiveness of using C2H6 as a proxy for O&G CH4 emissions. These limits could be resolved retroactively by increasing the availability of industry-collected gas composition data.
This study estimates the influence of anthropogenic emission reductions on nitrogen dioxide (NO_2) and ozone (O_3) concentration changes during the COVID-19 pandemic period using in-situ surface and Sentinel-5p (TROPOMI) satellite column measurements and GEOS-Chem model simulations. We show that, as a result of reductions in anthropogenic emission in eight German metropolitan cities, meteorology corrected mean in-situ (\& column) NO_2(2020,corr) concentrations decreased by 23 ± 4.7 % (& 16.4 ± 7.2 %) between March 21 and June 30, 2020, whereas meteorology corrected mean in-situ O_3(2020,corr) concentration increased by 4 ± 8.8 % between March 21 and May 31, 2020, and decreased by 3 ± 8.7 % in June 2020, compared to 2019 (uncertainty represents the 1 σ of mean changes of eight metropolitan cities). The impacts of meteorology on in-situ and TROPOMI NO_2 concentration changes during the lockdown compared to 2019 are relatively small (+0.4 % and -0.6 %, respectively), while those on in-situ O_3 concentration changes are more significant (+3.6 % and -13.5 % for March 21 to May 31, 2020 and June 2020, respectively). A NO_X saturated ozone production regime in German metropolitan cities in March to May explains the increased O_3(2020,corr) concentration in response to the decreased NO_2(2020,corr) concentration. This implies that future reductions in NO_X emissions are likely to increase ozone pollution in these cities if appropriate mitigation measures are not implemented. TROPOMI NO_2(2020,corr) concentrations decreased nationwide during the stricter lockdown period, except for North-West Germany, which can be attributed to enhanced NO_X emissions from agricultural soils.
Nitrate aerosol has become an increasingly important component of fine particles. While the formation and evolution of nitrate in airborne particles are extensively investigated, little is known about the formation of nitrate in clouds. Here we present a detailed investigation on the in-cloud formation of nitrate based on the size-resolved mixing state of nitrate in the individual cloud residual and cloud-free particles by single particle mass spectrometry, and the mass concentrations of nitrate in the cloud water and PM2.5 at a mountain site (1690 m a.s.l.) in southern China. The results show a significant enhancement of nitrate mass fraction in cloud water and relative intensity of nitrate in the mass spectra of the cloud residual particles, underlining a critical role of in-cloud processing in the formation of nitrate. Based on the size distribution of relative intensity of nitrate in individual particles, we exclude the gas phase scavenging of HNO3 and the facilitated activation of nitrate-containing particles as the major contribution for the enhanced nitrate. Regression analysis and theoretical calculations further reveal that nitrate is highly related (R2 = ~0.6) to the variation of [NOx][O3], temperature and droplet surface area in clouds. Accounting for droplet surface area greatly enhances the predictability of the observed nitrate compared with using [NOx][O3] and temperature. Our results indicate a critical role of in-cloud formation of nitrate via N2O5 hydrolysis, even during the daytime, attributed to the diminished light in clouds. The detailed observation would benefit future investigations of the evolution and oxidative impacts of nitrate.
During an extended volcanic unrest starting in 2017, two main moderate stratospheric eruptions occurred at the Ambae volcano (15°S and 167°E), Vanuatu, in April and July 2018. Observations from a geostationary orbit show that the April and July eruptions injected a volcanic plume into the lower stratosphere. While aerosol enhancements from the April eruption have only had an impact on the Southern Hemisphere, the plume from the July eruption was distributed within the lower branch of the Brewer-Dobson circulation to both hemispheres. Satellite, ground-based and in situ observations show that the background aerosol is enhanced throughout the year after the July eruption on a global scale. A volcanic-induced perturbation of the global stratospheric aerosol optical depth up to 0.012 is found, in the ultraviolet/visible spectral range. This perturbation is comparable to that of recent moderate stratospheric eruptions like from Kasatochi, Sarychev and Nabro. Top of the atmosphere radiative forcing values are estimated between -0.45 and -0.6 W/m2 for this event, showing that the Ambae eruption had the strongest climatic impact of the year 2018. Thus, the Ambae eruption in 2018 has to be taken into account when studying the decadal lower stratospheric aerosol budget and in climate studies.
Poor understanding of aerosol-cloud interactions and cloud feedback processes in the Arctic climate system limit our ability to constrain future climate in the region and one important knowledge gap is the source of particles upon which cloud droplets and ice crystals have formed. If representative cloud-water can be obtained from Arctic clouds, it’s chemical composition can be analysed to infer the sources of particles present within it. However, the balloon-borne active cloud water sampling systems required to obtain such samples have not previously been feasible due to their weight and the challenging environmental conditions. Here we present a miniaturised cloud-water sampler for balloon-borne collection of cloud water which was deployed during the Microbiology-Ocean-Cloud-Coupling in the High Arctic (MOCCHA) campaign in August and September 2018 along with the deployment protocol required to obtain representative samples in the pristine conditions encountered. We present the chemical composition of the samples obtained as well as the ice-nucleating activity of the samples and discuss the implications of our results on aerosol-cloud interactions in the high Arctic.
Fire emissions are an important component of global models, which help to understand the influence of sources, transport and chemistry on atmospheric composition. Global fire emission inventories can vary substantially due to the assumptions made in the emission creation process, including the defined vegetation type, fire detection, fuel loading, fraction of vegetation burned and emissions factors. Here, we focus on the uncertainty in emission factors and the resulting impact on modeled composition. Our study uses the Community Atmosphere Model with chemistry (CAM-chem) to model atmospheric composition for 2014, a year chosen for the relatively quiet El Niño Southern Oscillation activity. We focus on carbon monoxide (CO), a trace gas emitted from incomplete combustion and also produced from secondary oxidation of volatile organic compounds (VOCs). Fire is a major source of atmospheric CO and VOCs. Modeled CO from four fire emission inventories (CMIP6/GFED4s, QFED2.5, GFAS1.2 and FINN1.5) are compared after being implemented in CAM-chem. Multiple sensitivity tests are performed based on CO and VOC emission factor uncertainties. We compare model output in the 14 basis regions defined by the Global Fire Emissions Database (GFED) team and evaluate against CO observations from the Measurements of Pollution in the Troposphere (MOPITT) satellite-based instrument. For some regions, emission factor uncertainty spans the results found by using different inventories. Finally, we use modeled ozone (O3) to briefly investigate how emission factor uncertainty influences the atmospheric oxidative environment. Overall, accounting for emission factor uncertainty when modeling atmospheric chemistry can lend a range of uncertainty to simulated results.
The rate of rocket launches is accelerating, driven by the rapid global development of the space industry. Rocket launches emit chemically and radiatively active species into the stratosphere, where they impact ozone. We create a per-vehicle inventory of geographically-resolved stratospheric emissions for 2019, accounting for flight profiles and all major fuel types in active use. The inventory is used to simulate an intensive near-future scenario (120 launches/year at 17 current spaceports) with a chemistry-climate model. These gas-phase rocket emissions produce an overall 0.5% decrease in global annual-mean total column ozone. Compared to a reference scenario, Antarctic springtime ozone decreases by up to 9%. Arctic springtime ozone decreases by up to 5%; equivalent to half of the depletion observed over this region due to chlorofluorocarbons in the late 20th century. Our findings reiterate the need for assessment and international cooperation regarding the impact of space industrialization on Earth’s systems.
Particles containing meteoric material were observed in the lower stratosphere during five aircraft research missions in recent years. Single particle laser ablation technique in a bipolar configuration was used to measure the chemical composition of particles in a size range of approximately 150 nm to 3 µm. The five aircraft missions, conducted between 2014 and 2018, cover a latitude range from 15 to 68°N. In total, more than 330 000 single particles were analyzed. A prominent fraction (more than 50 000) of the analyzed particles was characterized by strong abundances of magnesium, iron, and rare iron oxide compounds, together with sulfuric acid. This particle type was found almost exclusively in the stratosphere and is interpreted as meteoric material immersed or dissolved in stratospheric sulfuric acid particles. Below the tropopause the fraction of this particle type decreases sharply. However, small abundances were observed below 3000 m a.s.l. in the Canadian Arctic and also at the Jungfraujoch high altitude station (3600 m a.s.l.). Thus, the removal pathway by sedimentation and/or mixing into the troposphere is confirmed. Our data show that particles containing meteoric material are present in the lower stratosphere in very similar relative abundances, regardless of latitude or season. This finding suggests that the meteoric material is transported from the mesosphere into the stratosphere in the downward branch of the Brewer-Dobson-Circulation and efficiently distributed towards low latitudes by isentropic mixing. As a result, meteoric material is found in particles of the stratospheric Junge layer at all latitudes.
The greenhouse gas footprint of oilfield flares comprises carbon dioxide and uncombusted hydrocarbons. It has been broadly assumed that oilfield flares are 98% efficient, and that the unburned fraction is predominantly methane. Recent studies have shown that neither assumption is necessarily true. Gas associated with tight oil production, now the largest source of flared gas in the United States, is a mixture of hydrocarbons in which methane is not necessarily more than half the total. Aerial surveys have found that while many flares function efficiently, a substantial fraction are very inefficient. This work builds on those studies to show how greenhouse gas footprints can be computed when flared gas is a mixture of hydrocarbons, and when flare efficiencies are best represented as statistical distributions. This work finds that the best estimate of GHG footprint of current Bakken oilfield flares is 56,400 tonnes carbon dioxide equivalent per day, compared to an estimate of 31,400 tonnes carbon dioxide equivalent per day under the assumption of 100% methane flares operating at 98% efficiency. Both these estimates considerably exceed the expected GHG footprint for flares based on data from the Environmental Protection Agency Greenhouse Gas Reporting Program.
Understanding the role of transport and photochemistry is essential to alleviate ambient ozone pollution. However, ozone budget and source apportionment studies often report conflicting conclusions — Local photochemistry is the main cause of ozone pollution based on the analyses of the former, while contrary, non-local ozone transported to the region accounts for the majority in the latter results. In order to explore its potential causes, we calculated the contributions of both processes to the variations of mean ozone concentration and total ozone mass (the corresponding budgets are noted as ozone concentration and mass budget, respectively) within the atmospheric boundary layer (ABL) of the Pearl River Delta (PRD), China, based on the modelling results of WRF-CMAQ. Quantified results show that photochemistry drives the rapid increase of ozone concentrations in the daytime, whereas transport, especially the vertical exchange near the ABL top, controls the ozone mass budget. The changes in transport contributions in ozone budgets indicate the influences of the ABL diurnal cycle and regional wind fields, including prevailing winds and local circulations (sea breezes), on regional ozone pollution. Though transport in our simulations had a relatively limited effect on ozone concentration, its high contribution to ozone mass increase in the morning determined that most ozone in the PRD emanated from the outer regions. Consequently, the role of transport and photochemistry in ozone pollution may differ, depending on which of the two budgets is concerned. For future studies targeting ozone and other pollutants with moderately long atmospheric lifetimes, we suggest that attention should be paid to budget-type selections.
Wildland fires involve complicated processes that are challenging to represent in chemical transport models. Recent airborne measurements reveal remarkable chemical tomography in fresh wildland fire plumes, which remain yet to be fully explored using models. Here we present a high-resolution large eddy simulation (LES) model coupled to chemistry to study the chemical evolution in fresh wildland fire plume. The model is configured for a large fire heavily sampled during the Fire Influence on Regional to Global Environments and Air Quality (FIREX-AQ) field campaign, and a variety of airborne measurements are used to evaluate the chemical heterogeneity revealed by the model. We show that the model captures the observed cross-transect variations of a number of compounds quite well, including ozone (O3), nitrous acid (HONO), and peroxyacetyl nitrate (PAN), etc. The combined observational and modeling results suggest that the top and edges of fresh plume drive the photochemistry, while dark chemistry is also present but in the lower part of the plume. The model spatial resolution is shown to be very important as it may shift the chemical regime, leading to biases in O3 and NOx chemistry. Based on findings in this work, we speculate that the impact of small fires on air quality may be largely underestimated in models with coarse spatial resolutions.
As the Arctic climate rapidly warms, there is a critical need for understanding variability and change in the Arctic carbon cycle, but a lack of long-term observations has hindered progress. This work analyzes and interprets measurements of atmospheric carbon dioxide (CO2) mixing ratios from long-term on-ice measurements (the O-Buoy Network), as well as coastal observatories from 2009-2016. The on-ice measurements show smaller seasonal amplitudes when compared to the coastal observatories, in contrast to the general observation of poleward increases of seasonal cycle amplitude. Average on-ice mixing ratios were lower than their coastal counterparts during the winter and spring months, contradicting the expectation that wintertime presents a poleward increasing gradient of CO2. We compare the observations to CO2; simulated in an updated version of the GEOS-Chem 3-D chemical transport model, which includes new tracers of airmass history and CO2; sources and sinks. The model reproduces the observed features of the seasonal cycle and shows that terrestrial biosphere fluxes and synoptic transport explain most CO2; variability over the surface of the Arctic Ocean. Interannually, the coastal observations were more comparable in overall CO2; growth than concurrent measurements over sea ice. We find evidence indicating the presence of ocean gas exchange in and around sea ice during periods where this growth discrepancy occurs. Periods with large spatial gradients are examined, showing that release of CO2; from Arctic waters in years with low sea ice concentration could possibly contribute to the greater interannual increase of CO2; over sea ice compared to land.