Published in IJCP December 2019
From the Desk of Group Editor in Chief
Pollution Solutions
December 16, 2019 | KK Aggarwal

Group Editor-in-Chief, IJCP Group

Severe levels of air pollution in North India is an annual affair now. This year as well, northern parts of the nation have dealt with dangerous levels of air pollution. However, the problem is not restricted to North India. Vehicular pollution and pollution caused by emissions from industries is the same everywhere.

These dangerous levels of pollution are putting the health and lives of people at stake.

We need urgent measures and policy interventions to mitigate air pollution. Some of the common measures that people can take to reduce the levels of pollution as well as to safeguard themselves against the risks are as under:

  • Building Constructions
  • Use Carbon tiles to absorb gases on the roof.
  • Mix titanium dioxide (TiO2) in the concrete used. TiO2 is a semiconductor and acts as a photocatalyst. It harvests sunlight, particularly the ultraviolet component. Once activated by light, TiO2 acts as a catalyst for reactions involving atmospheric oxygen and water that leads to degradation of hazardous chemicals that come into contact with it. For instance, nitrogen oxides, a hazardous component in vehicle emissions, are oxidized into harmless nitrates. Of note, TiO2 is activated by UV light only and therefore latitude and geographical position affect its overall efficiency.
  • Conserve energy by making transparent glasses in windows to capture natural sunlight.
  • Encourage wet mopping and not dry mopping of floors.
  • Grow grass on pavements to control the dust.
  • Reduce plastic waste and convert waste thermocol to a useful product - Adhesive: Gum from petrol and thermocol (gasoline and Styrofoam).

Thermocol is a form of polystyrene used for packaging. It is thrown away after use as waste plastic.

Effect on Human Health

  • Styrene is released on the burning of polystyrene polymers including foam cups, meat trays, egg containers, yogurt and deli containers. Styrene gas can be absorbed through skin and lungs.
  • At high levels, styrene vapor has the potential to damage the eyes and mucous membranes.
  • It could potentially increase the risk of heart disease; aggravate respiratory disorders such as asthma and emphysema, cause rashes, nausea or headaches, damage the nervous system, kidney or liver, in the development system.

Thermocol is polystyrene [CH(C6H5CH2)]n by structure. Petrol and toluene can yield good quality adhesive as compared to that obtained from other solvents. It is simple to prepare an adhesive from these products and requires only a beaker, glass rod and balance.

It is difficult to deal with plastic waste as it is light weight and occupies more volume. Therefore, this technique seems efficient. It has been noted that petrol and toluene can form good quality adhesive and the conversion of waste thermocol to an adhesive is an economical, eco-friendly and efficient technique.

  • Use sodium alginate-silica fume in place of activated carbon as adsorbent: Combine a naturally abundant raw material, sodium alginate (a polysaccharide that can be extracted from seaweed and algae) with a high-volume industrial by-product, silica fume (a by-product of ferrosilicon or silicon metal alloy processing) to yield a ‘green’ adsorbent that is better than activated carbon.
  • Grow more plants and use plant-based eco-friendly products in place of synthetic chemical-based ones
  • Use neem oil pesticide spray: a) Take neem oil or neem leaf extract; b) Emulsify: Since neem oil does not readily mix with water, use an emulsifier like a mild liquid soap; c) Mix: To make 1 liter of general-purpose neem oil spray, mix 5 mL neem oil, 2 mL of liquid soap and 1 L of water.
  • Powdery mildew and black spot are common garden diseases. A common home remedy is ‘Cornell Formula’, with main ingredient as baking soda. It is made with 1-gallon water + 1 tablespoon baking soda + 1 tablespoon vegetable oil + 2 drops dish washing liquid: These ingredients are mixed together and then sprayed on the plant affected by fungus.
  • Use insecticidal soap - Mix the following ingredients thoroughly: 1 cup of oil, such as vegetable, peanut, corn, soybean, etc. + 1 tablespoon dishwashing liquid or other pure soap. Avoid any dish washing liquids which contain degreaser, bleach or those used for an automatic dishwasher. Mix 2 teaspoons of this soap mixture to every cup of warm water and put into a spray bottle.
  • Use masks if you are prone to respiratory allergy.

Types of Masks/Respirators

  • Masks that remove contaminants from the air: Air-purifying respirators (APRs) include particulate respirators, which filter out airborne particles and gas masks, which filter out chemicals and gases.
  • Masks that supply clean respirable air from another source are called air-supplying respirators (ASRs). They include airline respirators, which use compressed air from a remote source; and self-contained breathing apparatus (SCBA), which include their own air supply.

How to Make Gas Masks?

Wet cloth held over the nose and mouth will provide protection from smoke particulates by absorbing water-soluble gases (hydrogen cyanide, hydrogen chloride, sulfur dioxide, carbon monoxide). For wetting, use water, soft drink, any nonalcoholic beverages, urine (During World War I, Canadian soldiers being attacked with chlorine gas (water soluble mustard gas) were told to urinate into their handkerchiefs and to breathe through). The wet cloth will also take care of >10-micron dust particles.

Particulate Filters

Particulate filters are of three types: Disposable (N95); Reusable respirators (facepiece is cleaned and reused but the filter cartridges are discarded and replaced); and Powered air-purifying respirators (PAPRs) where a battery-powered blower moves the airflow through the filters.

Disposable particulate filters can again be of three types: N, P and R (N - no oil in atmosphere, R means oil-resistant and P means oil-proof).

Based on efficiency, particulate respirator can be 95, 99 or 100 (100: The filter is expected to trap 99.97 particles of at least 0.3 microns in diameter out of every 100; 99: Trap 99 particles of at least 0.3 microns in diameter out of every 100; and 95: Trap 95 particles of at least 0.3 microns in diameter out of every 100).

Remember: As the letter rating and number rating increase, breathing fatigue will increase. Typically, an end user will find an N95 respirator cooler, and easier to breathe through than N99 mask.

How to choose a particulate matter mask?

  • Surgical mask is intended to be worn to catch microorganisms shed in liquid droplets, is made from paper or other non-woven material and should be discarded after 8 hours use. They cover >5-micron particles. They are not designed to protect the wearer from inhaling airborne bacteria or virus particles. Flu virus is 0.17 microns in size but the droplet is >5 micron in diameter.
  • Cotton and gauze masks do not serve as surgical masks as they do not offer adequate filtration of microbes.
  • Dust masks are manufactured to protect against particulate matter and do not protect against chemicals such as vapors and mists. Wool, plastic, glass, cellulose and combinations of two or more of these materials may be used. These filters cannot be cleaned and reused and have a limited lifespan. They often have exhalation valve.

Mask material can be synthetic, polypropylene or fiberglass (provide laminar flow). Each has a defined GSM. Higher the GSM, smaller will be the pore size and higher will be the efficiency. More the efficiency, more difficult it will be to breathe.

How masks work?

  • Interception: When >0.4 µm particles following a line of flow in the airstream come within one radius of a fiber and adhere to it.
  • Impaction: When larger particles >0.4 µm unable to follow the curving contours of the airstream are forced to embed in one of the fibers directly; this increases as fiber separation decreases and air flow velocity increases.
  • Diffusion: Where gas molecules collide with the smallest particles, especially those below 0.1 µm in diameter, which are thereby impeded and delayed in their path through the fiber mesh filter.
  • Coating: Certain resins, waxes and plastics are used as coatings on the filter material to attract particles with an electrostatic charge that holds them on the filter surface.
  • Gravity and allowing particles to settle into the filter material.

For 0.3 µm most penetrating particle size, diffusion and interception predominate.

Shape of a Filter

Particulate filters are designed to keep the velocity of air flow through the filter as low as possible. This is achieved by manipulating the slope and shape of the filter (V shape) to provide larger surface area. A high efficiency particulate air (HEPA) filter can remove as much as 99.97% of all airborne particulates with aerodynamic diameter of 0.3 µm or greater. Some high-quality air purifiers have as much as 60 sq. ft of filter material folded inside their HEPA filter.

Types of HEPA Filters

According to the Institute of Environmental Science and Technology (IEST), about performance, there are 6 types – A, B, C, D, E and F (A and B - 99.97% at 0.3 micron; C - 99.99% at 0.3-micron, D - 99.999% at 0.3 micron; E - 99.97% at 0.3 micron and F - 99.999% at 0.1-0.2 micron. B and E are with two flow leak tests).

HEPA vs. HEPA-like or HEPA-type filters

They are not same as HEPA filters as they capture >2-micron particles. Most are available as Pleat fold, V or W to increase the surface area. One inch should have 7-folds (HEPA will have 74 folds in 2 feet). HEPA therefore requires a powerful blower to give pressure.

Understanding Air Purifiers

Air purifiers contain a HEPA filter and a fan device.

Fan device

Clean Air Delivery Rate (CADR): CADR rating indicates how quickly the air purifier can clean the air within a particular size room. An air purifier with CADR rating of 300 cfm will clean a room of 300 sq. ft much faster than an air purifier with CADR rating of only 200 cfm.

Ionizer makes CADR ratings false. Ionization is a process of sticking several small particles into a bigger one, but not trapping them. The bigger formed particles are dropped on the floor and wall. Without proper removal, these pollutant particles reach the air once again.

CADR rating is taken in cfm i.e., cubic feet per minute, or in m³/hour. CADR measurement is usually for pollen, smoke and dust. These three pollutants are not only small in size but also the most unwanted particles in the air.

CADR ratings only show the cleaning capacity, not the cleaning capability.

Air exchange per hour: Normally one needs 2-5 air changes per hour (clean the air every 12-30 minutes in a room). If you have severe allergies, asthma or COPD (chronic obstructive pulmonary disease), 5 air changes per hour are needed. For medical clinics, 10 exchanges per hour are needed.

CADR is based on the highest fan speed. When you run the air purifier on a lower fan speed, the room coverage will also decrease.

Three air changes per hour would require a system that produces 150 cfm or 9,000 cubic feet per hour. A medical clinic needs a minimum of 10 air changes per hour with a filtration system that produces 30,000 cubic feet per hour or 500 cfm.

Area of the room = length ´ width ´ height (5 feet long, 20 feet wide, 10 feet height = 1000 cubic feet).

Types of Filters

Carbon filters

Sodium alginate-silica fume in place of activated carbon Bitumen

Felt – It is a textile material produced by matting, condensing and pressing fibers together. Felt can be made of natural fibers such as wool or animal fur, or from synthetic fibers such as petroleum-based acrylic or acrylonitrile or wood pulp-based rayon. 10 GSM 3 mm cloth is required for 5-micron particulate matter.

Sofa foam sheet – It can potentially absorb pollution

Pre-filter: Electrostatic polypropylene air filter media: Synthetic air filter material can remove airborne particulates through a combination of air flow and a static triboelectric charge. This is similar to how iron filings stick to a magnet.

Activated carbon air filter media: It effectively removes and prevents odor/fume build-up in recirculated air through a method of adsorption.

Polyurethane foam air filter media: This is a resilient and flexible air filter material that can be reused. Polyester impingement air filter media: This is a synthetic air filter material of high strength and durability; a high volume of contaminants can be trapped within the fiber.

Coconut fiber can be used as an alternative filter media for the removal of pollutants as well as fungus as there are large number of micro-pores with standard surface area in coconut fibers.

Coconut-shell based activated carbons are predominantly microporous and are the least dusty, and are very efficient when it comes to organic chemical adsorption. Compared to other types of activated carbon, coconut-shell based activated carbon filters have the highest hardness, which makes them ideal for water purification.

Sizes of Some Impurities and Particles


Size (Micron)

Anthrax spores




Atmospheric dust




Beach sand


Bone dust






Copier toner


Corn starch


Fiberglass insulation




Metallurgical dust


Mold spores


Oil smoke


Typical atmospheric dust


Tobacco smoke




Fungal spores


Smoke from synthetic materials


Smoke from natural materials




Saw dust




Pesticide and herbicides


Radioactive fallout