Delhi is not any more the most polluted city in the world! Is that good news – not really, because the air here is not cleaner than it used to be, other cities in the world have just become worse. We breathe 12,000 l of air every day. It is vital for our health to make sure that the air we breathe is clean - as it is to make sure that the water we drink (3 l) is safe or food we eat (1 kg) is healthy. The main outdoor air pollutant in India is the ultrafine particulate matter. It is entering our lungs and blood circulation and creating several health problems starting from respitory irritation, reduced lung capacity and asthma ending up in cardiovascular disease and cancer. Ultrafine particulates are the
smallest particulates in the air that we cannot see or sense in our respitory system. The size of ultrafine particulate is 2.5 μm (PM2.5) or smaller. We can only see the dust particulates that are 30 times bigger i.e. 75 μm.

Another typical particulate size that is measured in outdoor and indoor air is 10 μm (PM10). The main sources of particulate matter in India are traffic (especially diesel cars), biomass combustion (e.g. chullah and waste and stable burning), open construction sites, coal power plants and some industrial processes. What is special in India is that particulate pollution is not only a problem in major cities but it is a rural problem as well (chullah and stable burning).Out of 124 cities in India where particulate levels are measured, 123 cities have higher annual average value than what WHO recommends (10 μg/m3). There are also some gases and metals in the outdoor air hat create health issues in high concentrations like Carbon Monoxide (CO), Nitrogen Dioxide (NO2), Ozone (O3), Sulphur Dioxide (SO2), Ammonia (NH3) or Lead (Pb). They are a problem in the areas where the traffic is heavy or some specific industries are located. These gases are among the particulate pollution basis of the Indian Air Quality Index (AQI) that is measured and calculated in major Indian cities by local Pollution Control Boards. Modern people spend 90% of their time indoors. It is therefore essential to make sure that especially the indoor air is clean.

The World Health Organization (WHO) report “The Right o Healthy Indoor Air (2000)” states: “Indoor air quality is an important determinant of population’s health and wellbeing. Exposure to hazardous airborne agents present in many indoor spaces causes adverse effects such as respiratory disease, allergy and irritation of the respiratory tract. That is why our responsibility is to provide healthy indoor environment foroccupants.” WHO reports that 1.3 million people die in India because of the indoor air pollution every year. In rural areas, open-fire cooking inside without chimney creates carbon monoxide and particulate pollution, which has been the main cause of mortality among women and children. Whereas, in most of the urban buildings the ambient air is the main sources of indoor air pollutant due to lack of air purification in the air intake.

Currently, all international ventilation standards (e.g. ASHRAE and EN) are based on the assumption that outdoor air is cleaner than the indoor air. This is why they recommend to improve indoor air quality (IAQ) by increasing the “fresh air” intake through mechanical ventilation system (e.g. LEED green building standard recommends +30% more outdoor air) or by improving the natural ventilation strategy. 

Inspite of the cleaner outdoor air, the ASHRAE and EU standards require much better filtration of outdoor air in a ventilation system. LEED recommends to use minimum MERV 13 (EU 7) filtration. The European standard EN 13779:2007 specifies the filtration based on targeted indoor air quality and the local outdoor air quality as follows:

• Indoor air quality (IDA):

1. IDA 1: High indoor air quality
2. IDA 2: Medium indoor air quality
3. IDA 3: Moderate indoor air quality
4. IDA 4: Low indoor air quality

• Outdoor air quality (ODA):

1. ODA 1: Pure air which may be only temporarily dusty (e.g.pollen);
2. ODA 2: Outdoor air with high concentrations of particulate matter and/or gaseous pollutants;
3. ODA 3: Outdoor air with very high concentrations of gaseous pollutants and/or particulate.

In India, indoor air quality cannot be improved merely by increasing the ventilation rate without proper ambient air particulate fi ltration. Particulate air filters are classifi ed as either mechanical filters (including electrostatically charged filters) or electrostatic precipitators (ESP). The present Indian “industry standard” in air handling units and treated fresh air units is to have washable MERV 8 (EU 4) filters only. Filtration is much below international standards despite the fact that ambient air is much more polluted (especially particulate pollution) than in North America or in Europe. Therefore, one of the most important issues to improve indoor air quality in Indian buildings would be to start using better particulate filters in the outdoor air intake. This means that especially the treated fresh air units (TFA) should have the improved filtration.

Ambient Air Purifier (fanfilter unit in AHU room’s air intake) is also an excellent retrofit concept for existing buildings with air handling units. This concept has been piloted in several buildings in Delhi (offices, schools and apartments) with excellent results. Due to the suffi cient amount of cleaned outdoor air and the properly balanced air flow rates in the ductwork, the building is in positive pressure and both particulate pollution and CO2-levels are low. The case studies shows that indoor air PM2.5 level stays 95% below outdoor air concentration. It means that indoor PM2.5 level is below 15 μg/ m3 as long as outdoor air concentration stays below 300 μg/m3. Simultaneously the CO2-level stays below 800 ppm. This kind of indoor air fulfi ls any of the indoor air quality standards in the world.

In case outdoor air gas levels are high, molecular filtration is required in outdoor air intake. The most common molecular filter is activated carbon filter, but in some cases the air purification requires chemical filters with other sorbents.Sorbent physicochemical properties—such as pore size and shape, surface area, pore volume, and chemical inertness—all influence the ability of a sorbent to collect gases and vapors. Sorbent manufacturers have published information on the proper use of gas-phase sorbents, based upon contaminants and conditions.

There are also indoor based pollutants like solvents, paints and other building materials as-well-as cleaning products. They may release Volatile Organic Compounds (VOCs) into the air and therefore the easiest way to improve the indoor air quality is to choose the low or zero VOC products only. Emissions are typically highest from new materials. This is why effective ventilation is critical, especially in new buildings, where continuous operation of the ventilation system is recommended, particularly during the first year of occupancy.

There are also a large variety of room air purifiers in the market. In some cheaper models the air flow rate is too low for proper room air cleaning. Especially dirty mechanical filters increases the pressure loss a lot and therefore reduce the air flow rate. There are also air purifiers that produces ozone. Ozone in large amounts can neutralize strong odors (such as the smoke odor from fire damage). But ozone is harmful to human health in high concentrations whether pure or mixed with other chemicals and therefore ozonizing air cleaners cannot be recommended in occupied spaces. Air purifiers that use ionization tend also to produce ozone as a byproduct, as-well-as the UV-lights used to remove bio-aerosols. The amount of ozonegeneration varies depending on the type of UV-light or the voltage used in ESP-unit. Therefore, it is recommended to always use a molecular filter as a last filter module inside the product. In the current scenario, each one of us is looking for solutions to breathe cleaner air and save lives. All of the solutions and technologies already exist, but are yet to be implemented in India. The HVAC community in India is in key position to take the onus in endorsing IAQ policies, educating people and providing solutions for cleaner indoor air. The time is ripe for us to step forward and breathe in life through healthier indoor air.