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Contrail cirrus radiative forcing for future air traffic

The climate impact of air traffic is to a large degree caused by changes in cirrus cloudiness resulting from the formation of contrails. We use an atmospheric climate model with a contrail cirrus parameterization to investigate the climate impact of contrail cirrus for the year 2050. The strong increase in contrail cirrus radiative forcing due to the projected increase in air traffic volume cannot be compensated for by the reduction of soot emissions and by improvements in propulsion efficiency.

Aerosol pH and its driving factors in Beijing

Aerosol acidity plays a key role in secondary aerosol formation. To provide a more comprehensive reference for aerosol pH and a basis for controlling secondary aerosol generation, this study used the latest data covering four seasons and different particle sizes to obtain the characteristics of aerosol pH and explore the main factors affecting aerosol pH and gas–particle partitioning in the Beijing area.

Global distribution of methane emissions, emission trends, and OH concentrations and trends inferred from an inversion of GOSAT satellite data for 2010–2015

We use 2010–2015 satellite observations of atmospheric methane to improve estimates of methane emissions and their trends, as well as the concentration and trend of tropospheric OH (hydroxyl radical, methane’s main sink). We find overestimates of Chinese coal and Middle East oil/gas emissions in the prior estimate. The 2010–2015 growth in methane is attributed to an increase in emissions from India, China, and areas with large tropical wetlands. The contribution from OH is small in comparison.

GOSAT satellite data for 2010–2015">Read more

Photooxidants from brown carbon and other chromophores in illuminated particle extracts

We measured hydroxyl radical (^•OH), singlet oxygen (¹O₂*), and organic triplets (³C*) in illuminated aqueous particle extracts. After measuring the impact of dilution on oxidant concentrations, we extrapolated our results to predict them in ambient particles –¹O₂* and³C* concentrations appear to be greatly enhanced, while^•OH appears largely unchanged. Two of these oxidants (¹O₂*,³C*) are not yet included in atmospheric models, and our results make it possible to include them in the future.

Northern Hemisphere continental winter warming following the 1991 Mt. Pinatubo eruption: reconciling models and observations

This study provides compelling new evidence that the surface winter warming observed over the Northern Hemisphere continents following the 1991 eruption of Mt. Pinatubo was, very likely, completely unrelated to the eruption. This result has implications for earlier eruptions, as the evidence presented here demonstrates that the surface signal of even the very largest known eruptions may be swamped by the internal variability at high latitudes.

Quantifying variations in shortwave aerosol–cloud–radiation interactions using local meteorology and cloud state constraints

Aerosols are released by natural and human activities. When aerosols encounter clouds they interact in what is known as the indirect effect. Brighter clouds are expected due to the microphysical response; however, certain environments can trigger a modified response. Limits on the stability, humidity, and cloud thickness are applied regionally to investigate local cloud responses to aerosol, resulting in a range of indirect effects that would result in significant cooling or slight warming.

Heterogeneous sulfate aerosol formation mechanisms during wintertime Chinese haze events: air quality model assessment using observations of sulfate oxygen isotopes in Beijing

Sulfate is a key species contributing to particle formation and growth during wintertime Chinese haze events. This study combines observations and modeling of oxygen isotope signatures in sulfate aerosol to investigate its formation mechanisms, with a focus on heterogeneous production on aerosol surface via H₂O₂, O₃, and NO₂ and trace metal catalyzed oxidation. Contributions from different formation pathways are presented.

Vertical and horizontal distribution of submicron aerosol chemical composition and physical characteristics across northern India during pre-monsoon and monsoon seasons

Our study, for the first time, presents measurements of aerosol chemical composition and physical characteristics across northern India in the pre-monsoon and monsoon seasons of 2016 using the FAAM BAe-146 UK research aircraft. Across northern India, an elevated aerosol layer dominated by sulfate aerosol exists that diminishes with monsoon arrival. The Indo-Gangetic Plain (IGP) boundary layer is dominated by organics, whereas outside the IGP sulfate dominates with increased scattering aerosol.

A new description of probability density distributions of polar mesospheric clouds

In this paper we present a new description of statistical probability density functions (pdfs) of polar mesospheric clouds (PMC). We derive a new class of pdfs that describes successfully the probability statistic of ALOMAR lidar observations of different ice parameters. As a main advantage the new method allows us to connect different observational PMC distributions of lidar and satellite data, and also to compare with distributions from ice model studies.

Permafrost nitrous oxide emissions observed on a landscape scale using the airborne eddy-covariance method

As frozen soil, called permafrost, increasingly thaws over the years, scientists have put much effort into understanding how this may increase carbon emissions, which would exacerbate climate change. Our work supports the emerging view that these efforts should also include nitrous oxide (N₂O), a more potent greenhouse gas. Using a low-flying aircraft to study thousands of acres of Alaskan permafrost, we observed average N₂O emissions higher than typically assumed for regions such as this.

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