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Halogen chemistry reduces tropospheric O3 radiative forcing

We model pre-industrial to present day changes using the GEOS-Chem global chemical transport model with halogens (Cl, Br, I). The model better captures pre-industrial O₃observations with halogens included. Halogens buffer the tropospheric forcing of O₃(RF_TO[~3~]) from pre-industrial to present day, reducing RF_TO[~3~]by 0.087 Wm⁻². This reduction is greater than that from halogens on stratospheric O₃(−0.05 Wm⁻²). This suggests that models that do not include halogens will overestimate RF_TO[~3~]by ~ 25%.

Decadal changes in global surface NOx emissions from multi-constituent satellite data assimilation

Global surface emissions of nitrogen oxides (NO_x) over a 10-year period (2005–2014) are estimated from assimilation of multiple satellite datasets. We present detailed distributions of the estimated NO_xemission distributions for all major regions, the diurnal, seasonal, and decadal variability. The estimated emissions show a positive trend over India, China, and the Middle East, and a negative trend over the United States, southern Africa, and western Europe.

Snow fracture in relation to slab avalanche release: critical state for the onset of crack propagation

Based on DEM simulations we developed a new model for the onset of crack propagation in snow slab avalanche release. The model reconciles past approaches by considering the complex interplay between slab elasticity and the mechanical behavior of the weak layer including its structural collapse. The model agrees with extensive field data and can reproduce crack propagation on low-angle terrain and the decrease in critical crack length with increasing slope angle observed in numerical experiments.

Representing nighttime and minimum conductance in CLM4.5: global hydrology and carbon sensitivity analysis using observational constraints

Earth’s terrestrial surface influences climate by exchanging carbon and water with the atmosphere through stomatal pores. However, most land-surface models, used to predict global carbon and water fluxes, estimate that water lost through stomata is less than what observations show. In this study, we integrate plant water loss data from 204 species into a global land surface model, finding that global estimates of plant water loss increase, soil moisture decreases, and carbon gain also decreases.

Determination of the atmospheric lifetime and global warming potential of sulfur hexafluoride using a three-dimensional model

Sulfur hexafluoride (SF₆) is a very potent greenhouse gas, which is present in the atmosphere only through its industrial use, for example as an electrical insulator. To estimate accurately the impact of SF₆emissions on climate we need to know how long it persists in the atmosphere before being removed. Previous estimates of the SF₆lifetime indicate a large degree of uncertainty. Here we use a detailed atmospheric model to calculate a current best estimate of the SF₆lifetime.

Chemical oxidative potential of secondary organic aerosol (SOA) generated from the photooxidation of biogenic and anthropogenic volatile organic compounds

Secondary organic aerosols (SOA) comprise a significant fraction of particulate matter (PM) and may have health implications. The water-soluble oxidative potentials of various SOA systems were determined using dithiothreitol consumption. Results from this study demonstrate that precursor identity was more influential than reaction condition in determining SOA oxidative potential and highlight a need to consider SOA contributions from anthropogenic hydrocarbons to PM-induced health effects.

SOA) generated from the photooxidation of biogenic and anthropogenic volatile organic compounds">Read more

Radical chemistry at a rural site (Wangdu) in the North China Plain: observation and model calculations of OH, HO2 and RO2 radicals

In this study, we performed accurate OH measurements as well as selective HO₂ and RO₂ measurements at a rural site in North China Plain with state-of-the-art instruments newly developed. We confirmed the previous discovery on the enhancement of the OH in low NO_x with which little O₃ production was associated, and we found a missing RO₂ source in high NO_x which promoted higher O₃ production. Our results are of vital importance for ozone abatement strategies currently under discussion for China.

A comprehensive one-dimensional numerical model for solute transport in rivers

In this study a comprehensive model was developed that combines numerical schemes with high-order accuracy for solution of the advection–dispersion equation considering transient storage zones term in rivers. In developing the subjected model (TOASTS), for achieving better accuracy and applicability, irregular-cross sections and unsteady flow regime were considered. For this purpose the QUICK scheme due to its high stability and low approximation error has been used for spatial discretization.

A missing source of aerosols in Antarctica – beyond long-range transport, phytoplankton, and photochemistry

This paper summarizes two field measurements of particles and gases made in coastal Antarctica and represents the first real-time composition measurements of particles in this understudied area of the world. Using the combined data from both field measurements, we find that there is a constant background of particles in coastal Antarctica and that they are mostly sulfate. Seasonal transitions from winter to spring add additional particles, and that from spring to summer adds additional sulfate.

Model sensitivity studies of the decrease in atmospheric carbon tetrachloride

Carbon tetrachloride (CCl₄) is a compound which, when released into the atmosphere, can cause depletion of the stratospheric ozone layer. Its emissions are controlled under the Montreal Protocol, and its atmospheric abundance is slowly decreasing. However, this decrease is not as fast as expected based on estimates of its emissions and its atmospheric lifetime. We have used an atmospheric model to look at the uncertainties in the CCl₄lifetime and to examine the impact on its atmospheric decay.

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