Introduction

In the shadowy realm of modern science lies a phenomenon both ubiquitous and enigmatic - the aerosol. To the casual observer Aerosols are  mere mists, a fleeting wisp escaping from a canister or wafting through the air. In our bustling world aerosols pervade our lives, from air fresheners to potent industrial emissions. From laboratories to boardrooms, from classrooms to the corridors of power, the implications of Aerosol science are profound. In this article we give a brief outline of this product and the implications of its usage.

Aerosols are colloidal systems. One familiar example is when the dispersed phase ( payload or contents) is a liquid or solid and the dispersing medium ( propellant) is in the form of a gas. Smoke from an automobile exhaust, mist, fog are examples of aerosols. The illustration  above depicts  the dispersal of paint from an sealed aerosol canister(can). Liquid paint is forced up the tube due to the  propellant (CFC) under high pressure. By depressing the button at the tube’s end, the valve opens. Contents of the tube are then dispersed into the atmosphere through a small opening  forming a  spray or mist.  Control over the spray volume is facilitated by the button. Aerosol cans are typically constructed from thin sheet steel with an internal coating of tin.  However, aluminium cans are generally used for more expensive items necessitating a premium aesthetic, such as personal care products. The can’s internal pressure is maintained constant. This ensures the spray remains consistent even when the contents are depleted.  Proper operation requires the can to  be held upright during spraying.

Propellant and Contents

For  effective sprays , the propellant should posses  a higher vapour pressure and lower boiling points. They must adequately dissolve  with the contents, and  remain chemically stable under the conditions present within the canister. Chemical instability could lead to decomposition, reactions with the contents or changes in performance over time.  Additionally, they should be non - toxic, low ODP ( ozone depletion potential), low flammability types. Choosing a propellent with all these characteristics poses significant challenges, thus highlighting the complexities of Aerosol science. Common propellants and their compatible  contents include :
 

CFC ( Chlorofluorocarbons). Once prevelent as propellents in products like  pesticides, paints and air freshners, have been phased out due to their ozone depleting nature.

Environmental impact of Aerosols

Propellents harming the envoirnment due to Aerosol dispersions from canned products were mainly chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs) and Halon. Halon was very effective as a fire extinguisher.  Aerosol research has enabled the substitution of these propellants  to a large extent. They were known to cause depletion of the ozone layer leading to global warming. The smoke emanating from chimneys of a coal fired power plant are also Aerosols. They contain NOx and SOx gases that lead to acid rain. Many countries have regulations  restricting or banning the used of certain propellants, especially those deemed harmful to human health or environment.

Cautions

Aerosol propellants  can pose  fire and  explosion hazards , since they may be a typical combination of ignitable materials. Some of them could cause intoxication when inhaled. Spray dusters called “ Canned Air” , can sometimes be fatal if inhaled directly. They are typically used for cleaning electronic circuits especially in hard to reach areas and tight spots. The name can mislead people. In reality, they do not contain air. A spray, when released from the canister nozzle,  undergoes rapid adiabatic expansion, resulting in a drop in  temperature . It may cause frosting when directed to the skin. Therefore it is advisable to thoroughly review all details, particularly cautionary information, before usage.


Conclusion

From the intricacies of respiratory health to the balance of Earth’s  climate, aerosols have a role to play. We probably have more questions than answers. Yet admist the fog of uncertainty, one aspect remains clear - the imperative of continued inquiry and vigilance. We should not view aerosols as a barrier to progress, but as a beacon where science and society march hand - in - hand towards a brighter tomorrow. There lies both peril and promise, a reminder that in the delicate balance of nature and human endeavour lies the key to our shared destiny.