Some areas in the Mumbai Metropolitan Region feature extremely unhealthy levels of NO2, way higher than Punjabi Bagh in Delhi which reported hazardous Air Quality Index of 999 on Thursday

The killer smog returned to Delhi earlier this week, triggering near-zero visibility at several places and accidents on highways, and causing respiratory problems to Delhiites. While it has turned the national capital region into a chock-a-block a comparison of air quality data with the Mumbai Metropolitan Region (MMR) shows that the financial capital of India and areas around it aren't as safe as thought to be especially when it comes to levels of air pollutants Nitrogen Dioxide (NO2) and PM 2.5 (particulate matter with size lesser than 2.5 micrometres), two of the six major pollutants that lead to the formation of smog.

Punjabi Bagh in Delhi featured the poorest AQI on Thursday at 999, followed by RK Puram with an AQI of 868. The levels of PM 2.5 was equally high at 751 and 602 respectively. The PM10 was also at hazardous level touching 999 in both the locations.

Following that the Union Health Ministry on Wednesday issued an advisory in view of the severe air pollution in Delhi, asking children and persons with breathing difficulty to not venture out in the open in the capital. Latest data show that the quality of air is not at its best levels in the Mumbai Metropolitan Region either.

A comparison of air quality data of the two regions, in fact, shows that some areas in the MMR feature extremely unhealthy levels of NO2 way higher than several of the areas in the national capital which reported very poor air quality index over the last week.

In all the 10 weather stations which reported air quality data, and were part of the study for this report, the levels were above the severe level (251-350) set according to an Air quality inedxing labelling system developed by System of Air Quality and Weather Forecasting And Research (SFAR) at Indian Institute of Tropical Meteorology in Pune. Punjabi Bagh, RK Puram, ITO, Mandir Marg, Anand Vihar, Dwarka, Siri Fort, Shadipur, Delhi Technological University (DTU) and Institute Of Human Behaviour And Allied Sciences (IHBAS) all recorded over 400 levels for PM 2.5.

In Mumbai, the levels for PM 2.5 were not as severe as reported in Delhi, but they touched "very poor" levels.

The PM 2.5 levels in Mazgaon, BKC, Borivli, Navi Mumbai, Andheri and Bandra stations were "very poor" in five of the nine stations, which reporterd air quality data. The levels were reported highest in Mazgaon and Navi Mumbai at 192 µg per cubic metres and 192 µg per cubic metres respectively.

When it comes to NO2, Navi Mumbai performed the worst touching 149 parts per billion. The Air Quality Index crossed the good + satisfactory levels in Dombivli and Bandra as well.

According to Environment Protection Agency, the smaller the size of particulate matter, the more damaging they are for your health.

High levels of NO2 is damaging for lungs. NO2 inflames the lining of the lungs, and it can reduce immunity to lung infections. This can cause problems such as wheezing, coughing, colds, flu and bronchitis.

Mumbai's proximity to the sea prevents formation of fog in the region (as well as smog), thus often goes unnoticed, but the PM2.5 levels are still very high and hence not as safe as we may thought it to be.