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Assessment on Black Carbon and Tropospheric Ozone
Limiting short term climate change and improving air quality

Black carbon (BC) and ozone in the lower troposphere are pollutants that can have harmful impacts on human health and ecosystems and also contribute to climate change.

Black carbon is a component of the atmospheric aerosol particles and is the product of the incomplete combustion of fossil fuels and biofuels. Black carbon has various sources such as exhaust from cars and trucks, industrial plants, residential stoves, forest and savanna fires. Although it is not a greenhouse gas, it warms the atmosphere by absorbing sunlight. Deposited on snow, BC makes it dark and accelerates its melting. It can also influence cloud formation and has a negative impact on human health.

Ozone (O3) is a gas that exists in two layers of the atmosphere: in the stratosphere (the upper layer) it protects life on Earth by absorbing harmful ultraviolet radiation, while in the troposphere (the layer close to the planet surface up to 10-15 km) it is harmful to human health and ecosystems. In this layer it is also a greenhouse gas that contributes to atmospheric warming. Besides tropospheric O3 can harm the functioning of lungs and interfere with the respiratory system. At high concentrations it can also negatively affect crop yields; thereby decreasing food production. Ozone is not directly emitted from sources but is formed in the atmosphere from precursors that have natural and anthropogenic origins, such as Methane (CH4), nitrogen oxides (NOx), volatile organic compounds (VOC) and carbon monoxide (CO). 
Black carbon particles and ozone have a lifetime ranging from hours to days, so a reduction of the emissions of black carbon and of the precursors of tropospheric ozone will immediately reduce their concentrations in the atmosphere, with immediate benefits for climate and air quality. 


Finding measurements to benefit Climate Change and Air Quality

Applying current air pollution policies, the global emissions of black carbon and ozone precursors are expected to increase or at least remain at their present levels. For this reason, UNEP (United Nations Environmental Programme) and WMO (World Meteorological Organization) initiated a study to investigate which emission reduction measures could provide an improvement in air quality while also benefiting the climate. This study convened more than 50 scientists, including those from the IES, to assess policy options to address these air pollutants. Based on available current technology the implementation of the selected emission control measures is feasible. These emission control measures target the reduction of methane, BC and ozone precursors’ emissions, and if they are immediately implemented will contribute to rapidly reducing average global warming by 0.5 °C by 2050. As a result this could dramatically reduce premature death  due to air pollution and at the same time and increase annual crop yields significantly.

Although the application of these emission control measures would result in an immediate short term benefit for climate change, the temperature would soon start increasing again due to the continuous growth of greenhouse gases. Only if climate change policies are also rapidly implemented with immediate reductions of carbon dioxide (CO2), methane and the other greenhouse gas emissions, can the target of keeping the increase in global atmospheric temperature below 2°C (compared to pre-industrial times) be reached. This target, agreed upon during the United Nations (UN) climate change negotiations in Cancun in 2010, must be complied with if we are to manage the effects of climate change in a sustainable way.

Modelling air quality and climate change

As a contribution to this UNEP-WMO study, the IES developed and implemented models to evaluate the anthropogenic impact on climate change and air quality. The General Circulation Model ECHAM5-HAMMOZ was applied to study how changes in the emissions due to human activities can influence the present and the future climate. Calculations of the impacts on population exposure and on crop yields around the world have also been made using a chain of models.

The difference in surface  fine particles in the (ambient) air 2.5 micrometres or less in size( PM2.5) by 2030 resulting from two different scenarios: one including emission reduction measures, the other reflecting the result of implementing current policies on their own.



Contact Info:

Elisabetta Vignati - Tel: (+ 39) 0332 789414   Email: elisabetta.vignati(at)

Science for the Environment Quality  Fire Risk