Post 528 – by Gautam Shah


An interior space is finite and a well-controlled entity. It is a safe place against many of the threats to survival, but for the quality of air. The finite volume depends on outside environment for dilution of contaminants that are generated internally. It depends on controllable openings to filter out the external fouling elements. The interior space is a finite and predictable place and so both the processes can be managed. Indoor air pollution is often 2 to 5 times as bad as outdoor pollution. In few cases it is as worse as 100 times than the outdoors. Same holds true for Humidity, indoor humidity levels are higher then outdoors, except during the rain or just after a downpour, when it can be more for a while. When both, the internal and external environments are not appropriate, one has to rely on electro-mechanical or chemical filters or scrubbers.

Photograph of a model of the ancient city of Linzi in the Museum of the Qi State (The Qi city of Linzi was one of the largest and richest of the Spring and Autumn Period) > Climate dominated dwellings group Wikipedia image by Author Rolfmueller

One of the best and passive way is to continuously refresh the interior environment with the exterior air. Nominally an exterior air has proportionately lesser pollutants due to greater volume and dilution. But that may be highly contaminated at certain times, seasons and places. One of the major fouling factors of external environment is the street level condition. High speed moving traffic, even where non-fossil fuels are used, raises the dust level with air turbulence. Street level doors such as entrance foyers are used as escape points for used air, to reduce the casual intake of street level contaminants.

Jorasanko Mansion – Kolkata where Indian poet and Nobel laureate Rabindranath Tagore was both born and died >Warm humid climate hard surface courtyard. Wikipedia – Flickr image by Author Mark Kobayashi-Hillary

An interior space is perceived to be safe whenever there are excessive external pollution and associated discomfort. The interior space, however, has a finite volume and can support human occupation for a while, before it gets fouled up. One has to depend on dilution exchange with external environment. The external environment can be locally conditioned with use of elements such as green foliage or plants, water bodies, built baffles, better oriented and comparatively taller intake openings.

Passive air movement is one of the best means of diluting the interior pollutants. For air movements, the human settlements are planned with macro wind-breeze movements over the terrain. But, when air movements within the buildings are considered, the scenario changes substantially. The micro air currents that help interior exterior exchange are chiefly governed by pressure-temperature differential across a profile of set of openings. The local pressure-temperature gradients arise due to the colour and texture of surfaces, shapes and sizes of architectural elements, size, shape and level of openings, and shadowing effect of projections. A water body or greenery outside an intake opening adds moisture and cools the temperature of intake air. Similarly a hard and dark surface on outward opening accelerates the ventilation effect.

Fatehpur Sikri, Near Agra India: Daftarkhana (Old Dak Bungalow) High ceiling room of Tropical architecture Wikipedia image by Author Anupamg

Passive air exchange works due to the difference across the exterior and interior air pressures and temperatures. In tropical areas and on warm days the exterior air replaces the interior air, but with few disadvantages. Exterior air is drier and can remove the interior moisture. It is warmer and so warm up the interior temperatures, and the high pressure air current can cause irritating skin sensation and affect the elders’ and infants’ body temperature mechanism. The air exchange can also advantageously reduce the high proportion of moisture, the temperature, and offer skin-feel comfort. For colder climes and colder days the air exchange through openings or leakages can decrease the room temperature, evacuate the moisture and cause localized body cooling through air droughts.

John Looney House Ashville, Alabama (The dogtrot, also known as a breezeway house, dog-run, or possum-trot, is a style of house that was common throughout the Southeastern United States during the 19th and early 20th C.) Wikipedia image by Author Chris

The interior air gets contaminated due to various activities of human (and animals) occupation, and in many instances even without it continues to get contaminated. Building materials, finishes, furnishings generate high volume of pollutants in their latent state. These are in the form of unwanted gases, moisture, volatile organic compounds (VOCs), odours, particulate matters, etc.

Indoor air quality control is achieved with reduction of volatile organic compounds (VOCs), and microbial impurities. Buildings depend on passive and mechanically powered means to achieve adequate exchange with cleaner air of the outdoors. Screen filters, scrubbers (water, air and active solid particles) and methods of isolation, are chief means of dilution. Proper selection of building materials, surface finishes, furnishing materials, and the maintenance techniques and products go a long way in upgrading the interior air quality. The degradation of building materials and residual products of maintenance increases several times when the surface temperatures are high such as near stoves, heating elements, thin body materials exposed to solar heating.

Low ceiling Rooms > Wikipedia-Flickr image by Author Rob Koopman

High volume rooms (such as with higher ceilings) are preferred in tropical dwellings, because these offer greater volume per (person) occupancy and so higher dilution of contaminants. The high volume also offers greater internal air movement or turbulence for better mixing of fresh air with contaminated air. Low volume rooms (such as with lower or barely adequate ceilings heights) are found in modern multistoried apartments and air-conditioned offices. Such low volume spaces economize on cooling-heating costs, but these are not working or adequately operational the quality of air deteriorates. The mixing effect due to turbulence is not able to ventilate all pockets, such as undersides of desks and cabinets. Such spaces have stagnant, moist and warm air, breeding ground for mosquitoes. Spraying mosquito repellents or insecticides only adds to the pollution.



Post -by Gautam Shah



An Interior Space has finite volume, but with very average level of air exchange with outside environment. Interior spaces can support a moderate level of human occupation and of certain intensity but for fixed duration. In excessively polluted localities it cannot offer the comfort and health safety beyond a limited period.


Quality of outdoor air determines the quality of Indoor air

Outside air is always fresher due to its infinite volume, air currents, solar radiation and other environmental processes of nature. Though external air in highly polluted surroundings could be inimical, during specific periods. For buildings, at micro climate level, the exterior air may be contaminated on specific sides and periods of the day.


Indoor air quality in buildings can be improved, by control at the source, by filtration techniques, and by passive and active means of ventilation to dilute contaminants. Inadequate exchange (ventilation) can increase indoor pollution level by not bringing in enough and quality outdoor air to dilute the pollutants in indoor air. High temperature, humidity levels and to some extent air movements also increase concentrations of some pollutants.


To refresh the interior environment, one needs passive and benign interaction with the exteriors. The benign interaction could be scheduled in terms of time, such as during periods when outside environment is better, or facilitating the exchange on faces that are less vulnerable to exterior fouling, such as off the road sides, terraces, etc.


Contamination of Interior Spaces is not related to occupancy, but it may continue in dormant periods also. Many of the contaminants evolve from building’s materials, furniture, furnishings, cleaning and maintenance products, and as after effects of processes (such condensation of vapours, deposition of airborne particles, bacterial growth, etc.). The contaminants include unwanted gases, excess moisture, volatile organic compounds (VOCs), odours, particulate matters, etc.


Poor indoor air quality can cause or contribute to the development of infections, lung cancer, and chronic lung diseases such as asthma. In addition, it can cause headaches, dry eyes, nasal congestion, nausea and fatigue. People, who already have lung disease are at greater risk.

Formaldehyde is a carcinogenic substance and also causes coughing, eye, nose, and throat irritation, skin rashes, headaches, and dizziness. It is a very common chemical group found in many substances such as adhesives, paints, dyes, processed and printed fabrics, carpets, upholstery, particle board, and plywoods. Formaldehyde continues to get released in the air. Similarly many types potentially harmful chemicals are emitted by household cleaning agents, personal care products, pesticides, paints, hobby products, and solvents. Such chemicals can cause dizziness, nausea, allergic reactions, eye, skin and respiratory-tract irritation.

bedroom-window-1434067_640Some simple strategies to improve Quality of Indoor Air

1 Design wise isolate areas of high contamination by controlled partitioning system from benign areas.

2 Recognize the role of cracks and crevices for micro ventilation in buildings of warm climates, compared with a tightly sealed entity designed to avoid heat loss in buildings of colder climates.

3 Schedule activities and locate processes in areas where passive exchange with the outdoors is available.

4 Interior Design must include products and processes with least or zero VOC emissions.

5 Use cleaning and maintenance products that emit low or zero VOCs.

6 Plan for Air Moisture Control by way of ventilation, diffusion and scrubbing.




Post –by Gautam Shah



Defilement of internal air occurs mainly due to the occupation of space by people, plants and pets (exhalation, body odours, excretion products odours, food preparation), gadgets, equipments, and building and furnishing materials. The quality of air is usually determined by people’s sensation to various odours present in the air. But certain harmful pollutants like carbon dioxide and radon cannot be perceived by people at even high concentrations.


Scooters_in_Taipei_street_06Quality of air is determined in two ways. There are Absolute standards that provide for ideal conditions for comfort and bio-survival. Relative standards provide ways for determining the qualitative difference between out door air and indoor air. Quality of outside air is generally superior because an infinite space and high speed winds are available for dilution to occur. Quality of internal air can be improved by diluting the proportion of pollutants in air, by replacing part of the fouled air with comparatively cleaner air; or by various mechanical and chemical scrubbers.

Old Farmhouse

Particulate matter is a major source of air pollution, which mainly but not necessarily, originates outside and penetrates inside through various cracks and openings. Particulate can be dust, fumes, mist or biogenic matter. Particles of diameters greater than about 75 microns settle down rapidly and are termed Grit. Particles of smaller than 50 microns may remain suspended and constitute Aerosols. An aerosol is a liquid or solid particle which is in a quasi stable suspension in air. Very fine aerosols may remain suspended for weeks, whereas larger aerosols may get deposited in minutes. The deposition (and movement) of very small particles (2 microns) is influenced by temperature gradient (through convective currents). The effect on health due to airborne particulate matter of biogenic origin such as fungi, moulds, bacteria, viruses, pollens are well known.


In modern artificially controlled environment buildings are well designed and sealed to eliminate waste leakages. Such spaces function well so far as the environmental systems operate. However, pollutants arising from building materials, aerosols settling down, degradation of biotic materials, evaporation of condensed moisture from air handling plants, etc. continue to be added to the internal environment. The process of addition becomes severe when the environmental systems are switched off, such as at night time, on off days and when there are power breakdowns. This situation also occurs when there is no casual ventilation of the space due to shutting of nominal openings like doors and windows.

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