# Introduction

As defined by Collins dictionary, Air quality is the degree to which air is suitable or clean enough for humans, animals, or plants to remain healthy.

Nowadays, the naturally pure air has become luxury privilege not everyone can get. Actually, with booming industry, resource and fossil fuels consumption, no one can breath anymore the air of the same purity as our ancestors could over centuries, at least, not without air filtration or regeneration of some kind. As an example, the global atmospheric level of Carbon Dioxide was exceeded 300 ppm in not so distant past, in 1950-s. In less than 70 years, in January 2019 mankind had managed to increase it up to 400 ppm. Although, this is still well below 1000 ppm which is maximum level for continuous exposure recommended by U.S. EPA and ASHRAE, with increased $CO_2$ level of ambient air the higher intensity of ventilation is required to maintain indoor air quality.

Carbon Dioxide is just one of many air pollutants, such as Nitrogens Oxides, Carbon monoxide, Sulfur oxides, Particulate matter, Volatile organic compounds, various chemical gases and others.

Each of the pollutants in the air affects human body in a few ways. Firstly, noxious gases contribute to metabolical stress the body has to withstand. Secondly, pollutants displace oxygen and create the danger of asphyxiation. For example, calculations had shown that increasing the $CO_2$ concentration up to 5% (50000 ppm) will reduces the Oxygen content from 20.9% down to 19.85%.

The air purity is the one of air-related factors which are influencing human comfort and health. Temperature, humidity, air flow and air exchange rate are four major air parameters which controlled in air conditioning and ventilation.

The are number of national and international standards and regulations which set requirements for temperature, humidity, air flow and allowed concentrations of various pollutants in the air of inhabitant premisses.

Unfortunately, nowadays there is no internationally accepted standard exists for Air Quality neither for outdoor nor indoor air.

ISO developed a new standard 16000-40 “Indoor air quality management system”. It is in the approval stage at the moment.

Studies of the pollutants effects and air quality on the human health have establish new correlations between the content of harmful substances in the air and respiratory, diseases, cancer and mortality. Harmful effect on the health of humans oxides nitrogen, sulfur and carbon, volatile organic compounds and particulates investigated in works by COMMITTEE ON THE MEDICAL EFFECTS OF AIR POLLUTANTS (2015), Zhao and Hongyan and others. (2017), Jacobson, Mark (2008), Saarni H and Pentti (2002) and many others.