Iran’s capital Tehran on Tuesday registered red air quality alert and ranked as the world’s fourth most polluted city where all population groups are at risk.

The air quality index stood at 162, considered to be “unhealthy” by world standards. This means the degree of the pollution hanging over the city is so high that it is dangerous for all groups, including healthy people.

All ten top-ranking cities on Tuesday were in Asia with two Indian and one Pakistani cities at the top three spots, followed by Tehran.

Mojtaba Khaledi, a spokesman for emergency services, said that due to air pollution calls for assistance have increased by 28 percent.

Iran’s capital and other large cities grapple with pollution most of the year and even occasional rains have a short impact on improving air quality. Most private and public vehicles are old, with three-decade-old technology because of long-running economic problems and government controls.

A new problem added in the past few years is burning of mazut, a heavy diesel fuel, which is banned in most of the world. Iran’s natural gas production is declining, and power plants are forced to use the dirty fuel. The country has the second largest gas reserves in the world, but lack of investment and technology are gradually reducing output.