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Ethane and propane are the most abundant non-methane hydrocarbons in the atmosphere. However, their emissions, atmospheric distribution, and trends in their atmospheric concentrations are insufficiently understood. Atmospheric model simulations using standard community emission inventories do not reproduce available measurements in the Northern Hemisphere. Here, we show that observations of pre-industrial and present-day ethane and propane can be reproduced in simulations with a detailed atmospheric chemistry transport model, provided that natural geologic emissions are taken into account and anthropogenic fossil fuel emissions are assumed to be two to three times higher than is indicated in current inventories. Accounting for these enhanced ethane and propane emissions results in simulated surface ozone concentrations that are 5-13% higher than previously assumed in some polluted regions in Asia. The improved correspondence with observed ethane and propane in model simulations with greater emissions suggests that the level of fossil (geologic + fossil fuel) methane emissions in current inventories may need re-evaluation. © 2018 The Author(s).

Ozone and methane are chemically active climate-forcing agents affected by climate-chemistry interactions in the atmosphere. Key chemical reactions and processes affecting ozone and methane are presented. It is shown that climate-chemistry interactions have a significant impact on the two compounds. Ozone, which is a secondary compound in the atmosphere, produced and broken down mainly in the troposphere and stratosphre through chemical reactions involving atomic oxygen (O), NOx compounds (NO, NO2), CO, hydrogen radicals (OH, HO2), volatile organic compounds (VOC) and chlorine (Cl, ClO) and bromine (Br, BrO). Ozone is broken down through changes in the atmospheric distribution of the afore mentioned compounds. Methane is a primary compound emitted from different sources (wetlands, rice production, livestock, mining, oil and gas production and landfills).Methane is broken down by the hydroxyl radical (OH). OH is significantly affected by methane emissions, defined by the feedback factor, currently estimated to be in the range 1.3 to 1.5, and increasing with increasing methane emission. Ozone and methane changes are affected by NOx emissions. While ozone in general increase with increases in NOx emission, methane is reduced, due to increases in OH. Several processes where current and future changes have implications for climate-chemistry interactions are identified. It is also shown that climatic changes through dynamic processes could have significant impact on the atmospheric chemical distribution of ozone and methane, as we can see through the impact of Quasi Biennial Oscillation (QBO). Modeling studies indicate that increases in ozone could be more pronounced toward the end of this century. Thawing permafrost could lead to important positive feedbacks in the climate system. Large amounts of organic material are stored in the upper layers of the permafrost in the yedoma deposits in Siberia, where 2 to 5% of the deposits could be organic material. During thawing of permafrost, parts of the organic material that is deposited could be converted to methane. Furthermore, methane stored in deposits under shallow waters in the Arctic have the potential to be released in a future warmer climate with enhanced climate impact on methane, ozone and stratospheric water vapor. Studies performed by several groups show that the transport sectors have the potential for significant impacts on climate-chemistry interactions. There are large uncertainties connected to ozone and methane changes from the transport sector, and to methane release and climate impact during permafrost thawing. © 2014 by the authors.

Model studies show that changes in photodissociation rates resulting from changes in ozone column densities induce changes in lower tropospheric ozone, which vary significantly with location and time of the year. The validity of the model results is tested against daily total ozone and ground level ozone at three selected stations (Samoa, Mauna Loa, and Hohenpeissenberg). Observational data for a period of more than 1 decade have been analyzed. Comparisons are made of model-simulated distribution of ozone and its precursors (NOx and CO) at the three stations. Further comparisons are made of observed and model-calculated sensitivity in surface ozone to reduction in ozone column densities. Calculations performed with a global-scale chemical transport model (CTM) with extensive ozone chemistry reproduce well the observed levels and seasonal distribution of NOx, CO, and ozone at remote background stations (Samoa and Mauna Loa) and at stations in more polluted regions (Hohenpeissenberg). A chemical box model is used to demonstrate the chemical link between surface ozone changes and changes in total ozone for different NOx levels. Model studies and analysis of the observational data show that ground level ozone at the remote, low-NOx stations of Mauna Loa and Samoa is correlated positively with total ozone, with an exception at Mauna Loa during winter months. A reduction in ozone column densities, which leads to enhanced photochemical activity, reduces ozone levels at ground level. The sensitivity of surface ozone to changes in total ozone is particularly large in the low-NOx regime at Samoa. An anticorrelation between ground level ozone and total ozone is found at the Hohenpeissenberg station both in the observational data and in the model results during wintertime with high NOx levels. Enhanced photochemical activity leads to enhanced ozone production. There is, however, a disagreement between the observed and CTM-modeled sensitivity in surface ozone to ozone column density during the summer months at Hohenpeissenberg. The strong anticorrelation found in the observations, giving increases in surface ozone at low ozone column densities, is not present in the CTM model studies. It is suggested that a correlation between low ozone column densities and stagnant high-pressure systems is an important cause for the observed anticorrelation. Copyright 2005 by the American Geophysical Union.