Kathmandu, June 14:

Ground-level ozone layer is getting thicker in the valley, posing serious health and environmental hazards, environmentalists said today.

They attributed the phenomenon to a surge in emission, fuelled by increase in number of vehicles in the valley.

Speaking at an interaction organised by the Environment and Public Health Organisation (ENPHO) on the impact of ground-level ozone, Anil Kumar Raut, an environmental researcher at the Windrock International, said, “The ozone layer is formed from the ground level up to the height of about 400 metres. It is formed when reaction takes place between oxides of nitrogen and the volatile organic compounds in the presence of sunlight.”

“Generally, vehicles and factories emit harmful gases, which turn into ozone.”

Constant exposure to ground-level ozone triggers various health problems. It stops the growth of plants and animals. According to a report published in the Atmospheric Environment Journal, the average concentration of the ground-level ozone in the valley is about 80 ppb. The WHO considers the concentration of over 50 ppb very harmful for health and environment.

Raut said the concentration is the highest during office hours, when a maximum number of vehicles are on roads. “If not addressed on time, the problem (of formation of ground-level ozone) will have a disastrous impact on human health and agriculture,” Raut said.