How air pollution affects surface solar radiation over decades – AirQualityNews

A new study led by a team of scientists from Switzerland and China suggests that changes in the amount of sunlight reaching Earth (surface solar radiation or SSR) over recent decades has been influenced by levels of air pollution. 

The changes in SSR, known as global ‘dimming’ and ‘brightening’ have been especially pronounced in China where a significant dimming effect was seen between the 1960s and the 1990s. This was seen to diminish and become a brightening in recent years. 

Studies found that the dimming effect was strongest under clear-sky conditions—meaning it wasn’t caused by clouds, but by pollution in the atmosphere. Water vapor was ruled out as a major factor, further pointing to aerosols as the main driver.

After around 2008, SSR levels began to brighten again, especially in clear-sky conditions. This matches the timeline of China’s efforts to reduce air pollution through stricter environmental policies. 

The study reveals that between 1950 and 1980, China, India, the USA, Europe and Japan were all in a dimming phase. The USA, Europe and Japan entered a brightening phase around 1980. China entered theirs around the start of this century, while India – the country with the worst air pollution on the planet, is still in a period of darkening.

A clearer understanding of this phenomena is has only recently begun to emerge, partly because not all satellite systems fully accounted for aerosol changes, so would often show different trends than those suggested by surface observations. The team point out that one of the main challenges going forward is ironing out the inconsistencies between these different data sources.

Martin Wild, a professor at the Swiss Federal Institute of Technology and lead author of the study said: ‘The causes for these dramatic changes are thought to be primarily due to increasing air pollution in the dimming phase, and due to the successful implementation of air pollution mitigation measures in the brightening phase.

‘China provides a conducive environment for understanding how air pollutants impact solar radiation. The country’s well-organised, long-term monitoring systems make it one of the most studied regions for dimming and brightening effects.’

Wang Kaicun, a professor at Peking University, added: ‘The solar energy at the Earth’s surface is an important renewable energy and its availability is a critical factor for vegetation growth and food production.’

The full research can be read here.

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