Ozone pollution from Asia isn't well understood, but may be damaging Arctic plants

Like other greenhouse gases, ozone also affects how heat is reflected or absorbed near the Earth's surface.

Ozone pollution in the Arctic can take anywhere between a few days to several weeks and months through slower mixing in the high latitude troposphere, says Professor Frode Stordal, Department of Geosciences, University in Oslo (UiO).

"Ozone can be formed in Asia and transported to the Arctic, or the ozone precursors can be transported to the Arctic and ozone being formed there. Asian contribution to Arctic ozone is thus a complex issue, which is not well quantitatively characterized," he says.

The researchers have been studying the impact of ozone on plants inside a phytotron – an enclosed greenhouse – for two years now. They found that clovers grown in experiments are more easily injured by ozone when they are exposed to nights that are not completely dark after ozone exposure.

Phytotrons have long been an incubator for world-leading research by plant scientists. Image: CSIRO

Phytotrons have long been an incubator for world-leading research by plant scientists. Image: CSIRO

"Ozone is known to cause injuries to membranes, proteins/enzymes and other parts of the plant cells," said researcher Ane Vollsnes at the Department of Biosciences at the University of Oslo (UiO) in an email.

"The longer periods of light per day in the Arctic is thought to give a higher dose of ozone entering the leaves since stomata are often open in light periods. The difference in ozone dose to plants growing in longer day lengths compared to plants growing at shorter day lengths has been demonstrated in model studies of plants from different parts of Europe," she added

Europe and America have significantly reduced emissions from combustion furnaces and internal combustion engines. However, in Asia, due to population growth and an increasing standard of living, ozone pollution continues to increase. The ozone from Asia is then moved by the strong westerly winds around the northern hemisphere.

The harmful effects of ground-level ozone on plants are well known. Studies have shown that the ozone, at ground level, reduces the production of wheat by seven to twelve percent, soybeans by six to sixteen percent, rice by three to four percent, and corn by three to five percent. Crop yield losses due to ozone could be as much as 15 percent in large wheat-producing areas of India and China. This is happening as world hunger is on the rise.

Brown patches on these potato leaves are evidence of moderate ozone damage, seen September 2015. Image credit: Danica Lombardozzi/National Center for Atmospheric Research

Brown patches on these potato leaves are evidence of moderate ozone damage, seen September 2015. Image credit: Danica Lombardozzi/National Center for Atmospheric Research

Ozone is not a natural pollutant, says Shambhavi Shukla, Senior Research Associate, Pollution Campaign team, Centre for Science and Environment. "It is formed on the road surface from the exhaust gases of vehicles."

Ozone mostly formed in the tropics, sub-tropics and near the equator because of the rise in temperature, she adds. Another source of ozone pollution is from landfills. Landfill fires increase during summer due to rapid oxidation which leads to the release of multiple pollutants. CSE analysed eight-hour average ozone data and found that 38 percent of the 36 locations monitored are exceeding the eight-hour average ozone standard this year in April, says Shukla.

"On some days, this number has gone up to 61 percent."

In 2018, out of the 32 locations monitored, 28 percent of the monitoring locations exceeded the standard at the same time. A report published by Health Effect Institute has shown that deaths due to ozone pollution jumped to 148 percent in India.

The centre notified the Comprehensive Action Plan, last year to combat pollution in Delhi-NCR. The plan has proposed actions and strategies under various categories like air quality monitoring, to reduce vehicular emissions, to reduce the number of vehicles on the road and non-motorised transport (NMT) which have to be implemented in a time bound manner.

This year, the Ministry Of Environment, Forest And Climate Change launched the National Clean Air Program (NCAP) to reduce particulate matter (PM) pollution by 20-30 percent in 102 cities across India by 2024. The program has been criticised as the targets set out are not legally binding. In the national capital, private vehicles ferry only 15 percent of the population but occupy 90 percent of road space.

Besides pollution, ozone does have a role to play in climate change.

"Ozone is a greenhouse gas impacting on infrared radiation from the earth's surface like any greenhouse gas. It absorbs some of the solar radiation, heating the surface," says Stordal. The researchers will also study its impact on the reflectivity of solar radiation of plants, evapotranspiration, and uptake of atmospheric carbon from CO2 in our project. The team wants to study natural vegetation and plants agricultural meadows and can then give advice to farmers about which cultivars to choose if they are concerned about the ozone pollution.

"In the present project we will study native species and our hypothesis is that they are more negatively affected by ozone when exposed to less dark nights during the Arctic summers, than on fully dark nights," says Stordal.

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