Scientists and environmental experts have highlighted the need for such advisories for years. They have repeatedly pointed out that an exercise to measure poor air quality, without educating people about the health risks associated with breathing it in, was a futile one.

“What is the point of providing data about air quality without an alert system that helps educate people about the necessary steps they should take? How does a layman translate the data into something that affects him,” asked Dr T K Joshi, director of the Centre for Occupational and Environmental Medicine at the Maulana Azad Medical College (MAMC).

Dr Joshi and several other experts were part of the central government’s committee to draft the National Air Quality Index (AQI), which was introduced over a year ago.

During the drafting process, experts had discussed the need for issuing advisories or an alert system, but these ideas never took any concrete shape, said sources.

Most global cities struggling with high pollution levels — including Mexico, Beijing, London and Los Angeles — have an effective smog alert system to augment their air quality data.

California was one of the first states to implement such a system in the 1980s after the first alarms were raised about deteriorating air quality in Los Angeles.

Sam Delson, deputy director of California’s Office of Environmental Health Hazard Assessment (OEHHA), said most vulnerable groups like children, the elderly and people with asthma and other chronic diseases, “can benefit significantly from avoiding exposure on particularly smoggy days,” from such advisories.

Such advisories are “a basic public health strategy for confronting air pollution,” said Dr Howard Frumkin, Dean at the School of Public Health and professor of Environmental Health Sciences at the University of Washington. “Air quality monitoring is important, but if the information generated doesn’t reach those who need to know and motivate protective action, then monitoring does little good,” he said.

According to Dr Joshua Apte, assistant professor at the University of Texas, such advisories would be beneficial for Delhi, due to the rapid real-time changes in air quality. “Pollution levels in Delhi can vary on an hour-to-hour or day-to-day basis. Health advisories can communicate the risks of pollution in a way the public can easily understand,”he said.

There is an “absolute” need for public health advisories, said Dr Bhargav Krishna, research fellow in Environmental Health at the Public Health Foundation of India. “Episodic high air pollution levels have been shown to exacerbate pre-existing respiratory and cardiac conditions. With pollution levels as high as Delhi has experienced over the past few days, exposure can be harmful even for those who don’t have pre-existing conditions,” he said.

The need of the hour seems to be an effective smog alert system, which would be particularly beneficial to children.

“Given the level of particulates in Delhi this month, the outdoor activities of children should definitely have been restricted. Children have bigger lungs in proportion to their body size, and hence inhale more amount of air,” said Dr Joshi. He advised people living near main roads or traffic intersections to avoid keeping their windows open during peak traffic hours.