Lahore on Monday ranked topped among global cities with bad air quality in the world, while Karachi stood on eighth number, according to air pollution data released by the US Air Quality Index.

The Punjab's capital recorded 264 AQI that classifies Lahore under the “unhealthy” category of air quality.

According to the United States Environmental Protection Agency, the air quality satisfactory if the AQI is under 50.

Air pollution in Lahore is caused by a combination of vehicle and industrial emissions, smoke from brick kilns, the burning of crop residue and general waste, and dust from construction sites. Other factors of air pollution include large scale losses of trees to build new roads and buildings.

Winter air pollution is worse due to temperature inversion, which results in a layer of warm air that is prevented from rising trapping air pollutants.

Air quality in Lahore usually worsens during the winter season from October to February when farmers in the wider Punjab province set light to the remnants of crops, producing smoke that adds to smog, read a report on the US AQI.

At the same time, weather changes mean pollutants remain trapped in the air for longer, it added.

The air quality can be improved by reducing industrial and vehicular emissions as well as reducing pollution from brick kilns.

The report further stated that individuals can take steps in their daily life to reduce personal emissions by carpooling or taking public transport and actively switching to greener fuel alternatives.