The Hydrogen Economy – and some reactions

Hydrogen in a low-carbon economy was published by the Committee on Climate Change in November 2018 

It is available at https://www.theccc.org.uk/publication/hydrogen-in-a-low-carbon-economy/

Its scope is indicated by its section headings, which are:

Hydrogen for heat in buildings and industry

Hydrogen use elsewhere in the energy system

Hydrogen supply

Scenarios for hydrogen use

Energy system cost implications, and

Conclusions and recommendations.

This post addresses only the penultimate paragraph of the report (p.126):

“Further work is required to establish whether and to what degree hydrogen acts as an indirect greenhouse gas if emitted to atmosphere.”

Some discussions around the effects of hydrogen emissions are to be found in an earlier publication

HyCARE Hydrogen Energy Chances and Risks for the Environment

Proceedings of the first HyCARE meeting, Hamburg, 16-17 December 2004, available at

https://pure.mpg.de/rest/items/item_994975_6/component/file_994974/content

Extracts from the proceedings are given below.

p.42 Hydrogen-Infrastructures: Feedbacks to Climate and Atmosphere

Martin Kaufmann et al. referred to “Leakages in the hydrogen transport and fueling system” which could “decrease the number of OH molecules and therefore the self purification of the troposphere”, but claimed that “this effect is comparatively small.”

p.46 Hydrogen, methane and ozone in the atmosphere – New challenges for atmospheric pollution studies in a changing society

Tuomas Laurila et al. claim that “Hydrogen economy may change the atmospheric hydrogen concentrations because … the direct hydrogen emissions will increase and ... the emissions from the combustion of fossil fuels, at least from the traffic fleet, will probably decrease … Generally, the changing atmospheric composition, including the methane concentrations, affects the concentrations of the hydroxyl radical, which is responsible for the main atmospheric sink reaction.”

p.50 Atmospheric Impact of a Future Hydrogen Economy and Proposal for Hydrogen Emission Scenario Calculations

Werner Zittel is mainly concerned with the effects of water vapour formed as a result of hydrogen emissions, but predicts that the “overall water vapour emissions of a future hydrogen economy will be in the same range as from today’s conventional energy supply system. Compared to natural cycles which emit each year about 525,000,000 Tg anthropogenic additions are in the range of 0.005% and can be neglected.

p.61 Possible Environmental Impacts of a Hydrogen Economy

N. J. Warwick et al.

“Changing from a fossil fuel to a hydrogen-based energy system will cause significant changes in the magnitude and composition of man-made emissions. These changes in emissions could have both positive and negative environmental impacts. For example, a significant reduction in carbon gases and NOx could improve urban air quality, whereas a rise in H emissions could increase the atmospheric lifetimes of greenhouse gases and raise stratospheric water vapour concentrations, thus influencing stratospheric ozone.”

p.65 Modelling the impact of a switch to H2 energy sources on chemical composition and climate

Slimane Bekki focussed “on the uncertainties on the impact of a switch to H2 energy sources on the chemical composition of the atmosphere, in particular the stratosphere, and on climate” and claimed that the “uncertainties are very large indeed ... previous studies based on 2-D model calculations (Tromp et al., 2003; Warwick et al., 2004) reached opposite conclusions concerning the impact of enhanced H2 emissions on stratospheric ozone.”

p.66 Changing to a Hydrogen Economy: Study of Atmospheric Impact (CHESAI)

Euan Nisbet and Frode Stordal

describe a proposal “for piloting work to assess the atmospheric risks and benefits of the hydrogen economy. Recent research in atmospheric chemistry has shown that increased hydrogen emissions may have profound atmospheric consequences, changing the oxidative, cleansing capacity of the air. Concerns include the effects on tropospheric chemistry, including ozone and air pollution, and the impact on stratospheric water content and ozone decline. Hydrogen is also an indirect greenhouse gas, as a result of its effect on the atmospheric methane burden. Many impacts involve trade-offs with emissions of other species, such as methane, carbon monoxide and nitrogen oxides. These trade-offs need to be understood.”

p.71 Hydrogen, the energy crisis, and climate change

Martin Schultz provides a discussion which includes the mechanisms by which

hydrogen is removed from the atmosphere:

(p.72) “Movement of hydrogen into the upper atmosphere and thence to space is negligible in terms of the global hydrogen budget. Instead, hydrogen is removed from the atmosphere largely through dry deposition at the surface and subsequent microbiological uptake in soils. The rate of uptake depends on microbial activity, soil texture and moisture content. This sink is largest in the northern hemisphere because of its larger landmass, and it is thought to account for about 75% of all hydrogen removal. The remaining 25% of hydrogen is removed through oxidation by hydroxyl free radicals (OH) in the atmosphere.” (The reactions involved are given in some detail.)

“These atmospheric reactions, which are closely linked, are important because they determine the capacity of the atmosphere to neutralise pollutants. The concentration of hydroxyl radicals is particularly important, since it is these radicals that begin the whole oxidative degradation process … More hydrogen in the atmosphere will tend to lower the concentration of hydroxyl radicals and so inhibit the capacity of the atmosphere to oxidise greenhouse gases and other pollutants.”