Explained: What is ‘Severe-Plus' air quality? Effect on health, GRAP

New Delhi, Nov 01: Delhi is battling a severe crisis as the Air Quality plunged to 'Severe-Plus' category. The Air Quality has deteriorated so much that a public health emergency had to be declared and the government is distributing masks.

Delhi is enveloped in a thick, toxic layer of smoke and haze, and the situation is extremely alarming. Experts likened the situation to living in a gas chamber. AQI entered the "severe-plus" or "emergency" category late on Thursday night. Pollution levels increased alarmingly overnight. At 8.30 am, the capital's overall air quality index stood at 459. It was 410 at 8 pm on Thursday.

'Severe-Plus' AQI: What does it mean?

The Air Quality Index (AQI), which takes into account five chief pollutants including PM10 and PM2.5, were alarmingly high on Friday or November 1. An AQI between 401-500 is considered ''severe'' and anything beyond 500 is ''severe-plus emergency''.

Air Quality Index (AQI) is a tool to showcase air quality status. It transforms complex air quality data of various pollutants into a single number and colour.

All the 37 air quality monitoring stations across Delhi recorded the air quality in the severe category on Friday morning. Bawana was the most-polluted area with an AQI of 497, followed by Delhi Technological University (487), Wazirpur (485), Anand Vihar (484) and Vivek Vihar (482). Neighbouring Ghaziabad was the most polluted city in the country, with the levels of PM2.5 reaching as high as 493. Greater Noida (480), Noida (477), and Faridabad (432) also breathed extremely polluted air.

Air Quality Index (AQI) categories:

The AQI has six categories. Each of these categories has a different level of health concern. For example, an AQI value of 50 is considered as 'good' air quality with little or no potential to adversely affect the health of the people of a particular area. The air quantity index takes into account five chief pollutants including PM10 and PM2.5.

• AQI between 0-50 is considered Good.
• AQI between 51-100 is considered Satisfactory.
• AQI between 101-200 is considered Moderately Polluted.
• AQI between 201-300 is considered Poor.
• AQI between 301-400 is considered Very Poor.
• AQI between 401-500 is considered Severe.

According to official data, the overall AQI in Delhi was 582 at 12.30 am.

AQI levels and likely impact on people:

• Good - Minimal impact.
• Satisfactory - May cause minor breathing discomfort to sensitive people.
• Moderately polluted - May cause breathing discomfort to people with lung disease such as asthma, and discomfort to people with heart disease, children and older adults.
• Poor - May cause breathing discomfort to people on prolonged exposure, and discomfort to people with heart disease.
• Very poor - May cause respiratory illness to the people on prolonged exposure. The effect may be more pronounced in people with lung and heart diseases.
• Severe - May cause respiratory impact even on healthy people, and serious health impacts on people with lung/heart disease. The health impacts may be experienced even during light physical activity.

What are PM 10 and PM 2.5?

PM is the short form for particulate matter. PM 2.5 and PM 10 levels means the measure of the size of particles (dust, fine ash or anything that is fine). PM 10 is particles of size 10 micrometres or less, and PM 2.5 means particles measuring PM 2.5 micrometres or less. 10 and 2.5 micrometres are diameter measurements of particles which are used to classify them in different categories. Particles narrower than 10 micrometres are hazardous because they can get deep into lungs, and some may even get into your bloodstream. Larger particles tend to be trapped in the nose, mouth or throat.

AQI values and effects on health:

The hazardous air pollution has become a serious health concern. At these levels, people may breathe faster. The number of inhalations per minute may increase which poses risk of inhaling even more pollutants. The air quality in Delhi would affect healthy people and seriously impact those with existing diseases like asthma. Asthmatic patients may need hospitalisation Those with an allergy to fine particles may start gasping, sneezing and making effort to inhale. The situation is grim.

"Not even one person in the city can claim that one is feeling healthy. The entire city is suffering from the consequences of living in a gas chamber. This is a 'Maha collective failure. Intake of every 22 micrograms per cubic metre of polluted air is equivalent to smoking a cigarette. So whether the PM 2.5 level is 700 or 300 units, the impact is still as bad. People need to take precautions, especially those suffering from asthma, bronchitis or other respiratory illness," reports quoted Dr Arvind Kumar, lung surgeon and head of Respiratory Department, Sir Ganga Ram Hospital, as saying.

What is the Graded Response Action Plan or GRAP?

GRAP means Graded Response Action Plan. It defines the measures to be taken based on air quality. It will be enforced by the Environment Pollution Control Authority (EPCA). Under GRAP, if the air quality continues to be in the "severe-plus" category for more than 48 hours, emergency measures such as odd-even car rationing scheme and banning entry of trucks would be taken.

Emergency measures will be automatically enforced in NCR if the level of PM2.5 breaches 300 micrograms per cubic metre and PM10 levels stay above 500 for two consecutive days. During 'very poor' air quality, it recommends banning diesel generators and parking fee increased by three to four times. It also lists a number of other measures such as closing brick kilns, stone crushers, hot mix plants and intensifying public transport services and increasing the frequency of mechanised cleaning and sprinkling water on roads.

What led to this situation?

There is no single straight forward answer to this. There are many factors that contribute to it like - emission from factories, power plants, exhaust by vehicles that run on fossil fuels, burning garbage, burning crop residue or stubble, etc. The low temperature in winter in regions around Delhi worsens the matter as the particles, smoke, smog settle down due to low temperature.

When was National Air Quality Index (AQI) setup?

The National Air Quality Index (AQI) was launched in New Delhi on September 17, 2014, under the Swachh Bharat Abhiyan. The Central Pollution Control Board along with State Pollution Control Boards has been operating the National Air Monitoring Program (NAMP) covering 240 cities of the country having more than 342 monitoring stations.

The earlier measuring index was limited to three indicators, the one being used currently or the new index measures eight parameters.