10 THINGS YOU STILL NEED TO KNOW ABOUT AIR POLLUTION

10 THINGS YOU STILL NEED TO KNOW ABOUT AIR POLLUTION

Three of the five agencies that studied the impact of the odd-even trial on Delhi's air quality suggest that fewer cars on the roads had helped clean the air. This may not be immediately obvious since myriad factors influence pollution levels. Jayashree Nandi explores the play of conditions and elements that makes the air we breathe dirty and dangerous

1 SOURCE

Leading source of pollution varies with climate

Are vehicles the lead pollutants, or is it dust? Or is it due to biomass burning? Among vehicles, is it the petrol or the diesel variant that pollutes more? All these factors could be true depending on the season, the weather, the location and time of day. For instance, pollution caused by petrol vehicles in winters is five times higher than it is in summers. Road dust that accounts for nearly 41% of all pollutants in summer contributes just 4% in winter. The data here shows the various sources of pollution are based on climate

2 SEASON

Pollution in winter not same as in summer or monsoon

Irrespective of emission patterns, the concen tration of PM 2.5 is invariably 40% to 80% higher in November, December and January and 10% to 60% lower in May, June and July, a 2012 expert study (Role of Meteorology in sea sonality of air pollution in megacity Delhi) says. For years, this pattern has remained consistent.

As it gets colder, wind speed falls and the air closer to the ground, typically full of toxic material, can't rise higher and disperse. Smoggy conditions result and traps the contaminants in the air we breathe.

The same trends are seen in a recent draft IIT Kanpur report that Delhi government had commissioned. The overall average concentration of PM2.5 in summer is around 300 g m3. In winter it is 375 gm3.

In summers, pollution in Delhi is largely caused by dust and flyash high on silicon, iron and other metals. These comprise nearly 20% of total PM2.5.

In winter, the composition of PM2.5 undergoes change.And, components such as silicon, iron and metals go down to only 3.5%. Secondary particles of sulphates and nitrates account for 28% of PM2.5. Combustion-related “total carbon“ from burning of garbage, from thermal plants, vehicle emissions account for 23%.

Levels of PM10, PM2.5 and NO2 are higher in most places in winters by about 25-30%, the report says.

In winters, concentrations of PAH, a highly toxic group of chemicals, also go up in the air adding to its impurity and noxious effect, the study says.

3 WEATHER

Pollution can be rain-washed The graph shows percentage change in monthly average PM 2.5 concentrations over various seasons. As summer draws, percentage changes increase, and there is significant chane in levels as the rains kick in.

4 POLLUTANT

Every pollutant not equally toxic

The presence of a pollutant in air is not necassarily life threatening. It becomes a killer only after its concentration breaches safety limits. As may as 4000 Londoners died of air pollution when the Great Smog hit the UK capital in 1952. This was mainly due to PM 2.5 and SO2 levels crossing all limits of safety. What makes matters scarier is a newfound pollutant, ultrafine particulate matter (PM1).Experts haven't yet defined a safety limit for this.

Natural air consists of different gases, including PM 2.5 and PM1. The problem arises when the levels of some of the more dangerous gases and elements breaches safety level.Human activity is usually to blame for such a rise although weather can also play a role.

The more lethal PM1 penetrates the lungs and enters the blood stream, a recent report of the Steering Committee on Air Pollution and Health Related Issues says.The study also clarifies that CO, ozone (O3), nitrogen oxide (NOx), sulphur dioxide (SO2) and volatile organic compounds are just as life threatening if their concentration jumps alarmingly .

Toxic air pollutants such as dioxins, benzene, arsenic, beryllium, mercury, and vinyl chloride are also strongly linked to cancer and birth defects. The US Environment Protection Authority (EPA) keeps an eye on 187 such pollutants.

“Air toxins are found in trace amounts and are extremely toxic even in very small quantities.That's why they're measured in nano grams, not micrograms,“ Anumita Roy Chowdhury , head of Centre for Science and Environment's clean air campaign explains. “Measures should be based on which pollutants are dominant in an area and how toxic they are.“

For instance, historical data suggests SO2 and CO levels aren't rising as significantly as PM 2.5 and NO2 in Delhi, which have serious cardiovascular and respiratory impacts. Similarly , pollutants generated from combustion are more toxic than those from natural sources such as road or windblown dust.

5 EXPOSURE

Air quality not same as exposure

While it may be diffi cult to assess the odd-even strategy's impact from ambient air quality data, experts believe exposure to vehicular emissions would've reduced due to fewer cars on the roads.The experiment validates the need to track exposure and not make a call on pollution levels based on ambient air data.

“Ambient concentrations are easier to measure,“ a health ministry report says, “but don't al ways represent t r u e human exposures.

“Dose -a measure of change in the body due to exposure to pollutants -can be an accurate measure of impact, but isn't available for many important pollutants.“

There is a long tradition of measuring pollution in places where not many people spend a lot of time such as the tops of post offices or other public buildings.

Exposure assessment takes the process of measuring air pollution to where people spend most of their time.

“Ambient monitoring data is especially useful for providing a long-term record of the overall level of pollution, and how that changes with respect to policies,“ the report says.But people don't breathe ambient air: They breathe the air wherever they happen to be. “True exposures can differ substantially from ambient concentrations for two major reasons: the time they spend outdoors is often close to major sources like traffic that tend to be underrep resented by ambient sites, and of course most people are in doors more often than outdoors.“

Fine particu late component have recently been classified as a cause of lung cancer by IARC (International Agency for Research on Cancer), which had already classified diesel combustion and the burning of coal (two main causes of household and ambient air pollution) as sources of carcinogens. Around 30% of all lung cancer deaths can be attributed to the joint effects of household and ambient air pollution, the report adds.

In order to quantify exposures, one can measure air quality in indoor and outdoor environments in which people spend time,“ says Joshua Apte, assistant professor, University of Texas at Austin, who conducted a study in 2014 on exposures at traffic points in the city by carrying his portable monitor in an autorikshaw.

7 TIME REFERENCE

Uniform benchmarks? Impossible

Agencies use varying references of their choice. For instance: Delhi Polution Control Committee considers January 2014 as reference for Delhi during odd-even scheme because weather condition prevail ing that year and not 2015 were similar to this year.But they aren't comparing this time's levels with last year's as it rained heavily in that period. Delhi government compares readings taken by its mobile vans with findings from 2015 of its stationary monitoring stations. But this may fail to throw up an accurate picture since pollution levels vary by location. Some say assessment should be of air quality before implementing the oddeven scheme and results post vehicular curbs. CSE is assessing whether air pollution levels are declining rapidly indicating dispersal. End of day, varying reference dates periods end up throwing up results that may be in conflict.

8 LENGTH OF OBSERVATION

Measure at a spot or along the route?

The largest health impact of air pollution comes from sus tained, long-term exposure to pollution over months. As pollution levels can vary sharply across a city, mobile monitoring can provide a useful way of seeing differences in exposure and health risks between neighbourhoods. However, as pollution varies by time, day, and even season, a brief measurement at one location provides only a glimpse of the pollution at a given moment. To represent longer term patterns, one should make repeated visits to the same location at different times of day and year. Example: The ambient PM 2.5 levels at Anand Vihar on Monday was around 529gm3 at 10am. The levels declined soon after to 291 micrograms, which means the overall levels for a day would have been much lower than 500.

9 TIME OF DAY

Yes, midnight high noon of pollution

In winters, air pollution levels peak at night and early morning. Typically , dirty air levels taper off mid-morning to post-noon. This is because of two reasons -diesel trucks ply through the city at night. The pollution they cause doesn't get dispersed. At night when it's cold and the wind speed low, matters are made worse. As the day gets warmer, things clear up a bit. During the day, emissions are mostly from waste burning and private vehicles.

Pollution levels in Delhi vary sharply by season and time of day . In general, PM2.5 levels are several times higher at night than during the day, and several times higher during winter than in summer or monsoon. Therefore, suggests Joshua Apte, scientist at University of Texas, comparisons between locations ought to be made at similar times of day and in similar seasons, ideally with at least a few repeat observations.

Parts of Delhi better than Shimla?

Air pollution levels vary dramatically with location. It's entirely possible to breahe air cleaner than say Shimla in some Delhi neighbourhoods. IGI airport, for instance, records “moderate“ levels even in winter when almost all other stations hover between “very poor“ and “severe categories.“ Proximity to emission sources and vehicular traffic determine this.

DELHI VS BEIJING

The two great Asian capitals are equally infamous for alarmingly high PM 2.5 levels. As per a recent WHO urban air quality database, Delhi is worse. A comparison:

READING AIR POLLUTION DATA

REAL TIME

Real-time concentrations of pollutants using ambient air quality data (overall air quality, not actual exposure). The instant values are a snapshot of how bad or good the day is and whether you should be exposing yourself to the outdoor air for long. People tend to compare instant values with standard (24 hr) which may not be accurate but gives an idea of how polluted the air is

24-HR AVG STANDARD

Compare 24 hour average levels with ambient air quality standard (24-hr), when reading concentrations of any pollutant (PM 2.5, NO2, SO2 etc).For instance: if the 24 hour average for PM 2.5 at Mandir Marg is about 300 gm3, the levels are five times the standard, where the standard is 60 gm3

AIR QUALITY INDEX (AQI)

AQI is a system that transforms the weighed values of individual pollution related parameters into a single number or set of numbers which is then represented by a set of colours and description. CPCB and SAFAR provide AQIs. These are self-explanatory since each AQI number is given a category--“poor,“ “moderate,“ “severe“ to describe the air quality. Agencies in US and Europe also provide a health advisory with each category. For example if the levels are “hazardous,“ US EPA recommends: “Everyone should avoid all physical activity outdoors...“

for more details visit  www.vayupure.com