Australian guide to indoor nox exposure which affects the human health literature review


Quality of air is a determinant in the quality of life, indoor air is important as people spend on average 80-90% of their lives in door (WHO, 2007). Indoor air quality began a long time but only been a health concern decades ago when awareness of contaminants presented in the air. The problem begins when the construction of building are highly insulated to conserve energy, which caused a trap to air intoxicants inside the building (E. Willard, 2005). This causes the exchange of outdoor to indoor to lessen and therefore the indoor air pollution builds up.

Indoor air quality is a complex issue as research indicates that there are over 900 contaminants presented in the air from various sources (E. Willard, 2004). The indoor environments are under the impact of constant interaction changes which is difficult to analyze. For example, the concentration is greatly dependent on temperature or humidity, if temperature increases, the concentration increases.

Sources of air pollution are important when considering health effects because they relate to individual and population exposures (R. E. Hester, 2008). A survey conducted to review the source of contaminants that lead to poor indoor air quality. The results given as: 53% inadequate ventilation 10% outdoor contamination, 5% microbial contamination, 4% building material contamination and13% others. (E. Willard, 2003)

This review aims to find out how the indoor air affects the air quality management with various air studies that have been used to examine ambient air quality. The objectives of the review are to study:

  • Sources of Nox exposure, both indoor and outdoor
  • Strucutres that influence the accumulation of NOx
  • Adverse health effects associated with NOx exposure
  • Human behavior in response to Nox exposure
  • Compare effects of max and min exposures

The review strives to explore the different types of sources that contribute to NOx pollution and the sources are not restricted to indoor sources as the air also flows from the outside to t he inside.  The objectives of the paper leads to the research of the human health behaviors once exposed to NOx and explore different types of legislations and regulations that have been set up to monitor exposure of NOx since it is necessary to compare the current and the past issues that contribute to NO managements.

Indoor Air Pollution studies

Indoor air pollution is contributed from either indoor or outdoor air. Inside a building, there are many factors that originate contaminants and build up to air pollution. From outside, air may enter the buildings which increase the air the pollution (Willard, 2008).

Concentrations of pollutants are variable depending on the time and place. The impact of indoor pollution consists of cigarette smoking, stove operation, burning of kerosene, and various determinants from building materials (reference needed).  The impact from energy conservation decreases air quality due to the declining rate of ventilation.

Air pollution and health’ by Hester (date), the studies of air pollution are determined by various ways and methodologies; they are as follow;

  • By chamber (human challenge) studies
  • By studies of morbidity
  • Studies of hospital admissions
  • Studies of mortality

In chamber studies, the effect of individual pollutants is studied alone or in combination with other pollutants under controlled conditions. This monitors doses accurately to deliver the effects of co-factors. Epidemiological studies are more informative about health from individuals and population level.  The main purpose of the air quality studies is to measure, control and determine the effects on the human’s health and the results and examinations from the air pollution studies which enable the authorities to regulate and control the air quality for the community at the safest conditions.

What is NOx?

NOx is a reference to oxides of nitrogen, which as air pollutants, consists of NO and NO 2 . Nitrogen Dioxide (NO 2 ) has the most contribution of human health issue at a higher magnitude to Nitrogen Oxide (NO) (National environmental health forum, 2007). Nitrogen dioxide can be found in various places such as the outdoors, motor vehicles, public places, inside an office and within the homes.  Nitrogen dioxide is formed naturally in the atmosphere and can be created as a by-product from human activities. Nitrogen dioxide can also be formed from oxidation of the atmospheric nitrogen by the ignition and the oxidation of ammonia. The combustion process converts the nitrogen fuel into oxide, such as nitric oxide. The Nitric oxide oxidizes into nitrogen dioxide from the presence of the ozone and hydrocarbons outdoors and the presence of hydrocarbons.  NO2 can react with other compounds in the atmosphere and thus forming inorganic and organic nitrates, such as nitric acid and peroxyacetyl nitrate (National environmental health forum, 2007).

NOx indoor sources

The exposure to NO x has been known to cause varying levels of symptoms, but depending on the levels of exposure and its exposure can be particularly harmful to people suffering from asthma, as it might trigger an asthma attack . If one suspects that they have been exposed to harmful amounts of NOx  it is important to contact a health-care provider as fast as possible.

At low concentrations, NOx has been shown to cause:

  • Eye, nose, throat and lung irritation
  • Shortness of breath
  • Nausea
  • Dizziness
  • Coughing
  • Fluid build up in lungs

At very high concentrations, the NOx has been shown to cause:

  • Reduced ability to oxygenate body tissues
  • Death
  • Spasms of respiratory tract
  • Unconsciousness
  • Burning and swelling of respiratory tract

NOx affects the human health

The equipment which measures NOx is available, but is it is usually too expensive and complex to use for the general public. The homes that are located near busy roadways or the coal burning power plants often have higher levels of NOx. But burning natural gas, smoking tobacco, the kerosene, or the wood inside homes increases the concentrations of NOx. By avoiding the sources of the indoor NOx, it is often the best way to limit the indoor concentrations. Some easy recommendations to reduce exposure include not smoking tobacco inside, limiting the use of wood burning fireplaces and limiting the usage of gas or the kerosene powered space heaters and stoves. To limit the indoor concentrations, it i9s recommended that one always ventilate devices that create NOx directly to the outside (EPA, 2005)

Epidemiological studies (Morgan et al, 1996) found significant effects of nitrogen dioxide on mortality and hospitalisation. Exposure studies show inconsistent findings with young children with asthma whom are most likely to be affected by nitrogen dioxide.

NOx sampling and monitoring

Studies are carried out to sample and monitor NOx to determine exposures to the human health over certain periods. Samplers collect nitrogen dioxide over period of time to measure the presence and concentration of the contaminant.

For the indoor sampling, indoor air are not as uniform as ambient air and the general methods that are used to sample nitrogen dioxide are; Chemiluminescence method (AS3580. 5. 1), electrochemical cell device, passive Palmes tube method (AS2365. 11) and passive badge method (AS2365. 1. 2). The Chemiluminescence method and electrochemical device allows sampling to provide continuous data which presents in 1 hour average. AS2365. 1. 2 presents data in short term averages of several hours and AS2365. 1. 1 show long term averages of several days. (National environmental health forum, 2007). The precision of data depends on the period of average system. One hour averages are more accurate to determine concentration of nitrogen dioxide. What are the differences between these methods, could add more information now such as comparing the results from different studies utilizing the different methods.

There are indirect sampling approaches to measure nitrogen dioxide where studies used questionnaires technique to examine the candidates. Questions would be related to the presence or absence to nitrogen dioxide sources and the intensity of their use. The estimations are compared to the data from a continuous outdoor monitoring. The data then gathered from all sites and analyzed to provide appropriate result for an indirect assessment method (World health organization, 2008).

Studies are not accurately presented with indoor monitoring data as limitations to the number of sites, amount of data, conformity of data average periods and uniformity of methods. This results in instability and inconsistency of data monitoring.

A study was compiled by the National Environmental Health Forum (1997), which examined data from 5000 indoor samples. Figure X show a compilation of  the data on NOx exposures in……. recorded. It shows those indoor peaks are dramatically higher than outdoor peak, also on a regular basis. 30 studies from USEPA (1993) found that average indoor nitrogen dioxide with no sources to be 71% in comparison to 61% of corresponding outdoor levels. It shows that peak indoor levels generally occur when most occupants are in that specific environment.

Figure X.  Nox exposures in ……(National environmental health forum, 1997)

Another table below shows the results from indoor nitrogen studies that represent the results in an expression of a percentage to the concentration of nitrogen.

National environmental health forum, 1997

NOx regulations and guidelines

The guidelines from the National Health and Medical Research Council (NHMRC) for nitrogen dioxide over a one hour period for the indoor levels should be at maximum of 0. 16ppm. Currently, the level of concern for the indoor is at 0. 3ppm (National environmental health forum, 2006). In 2002 the IPCS and the WHO Air Quality Guidelines from Europe recommended a lower 1-hour period guideline of 0. 11ppm.

Case Study

The air pollution is a very serious problem in Canada and the burning of fuels in vehicles and engines is a main contributor, especially in big cities and thus, the air pollution is harmful to the environment and the health of Canadians. Many families use gas to heat up their houses as well as kerosene stoves and this contributes to much of the NOx emission. At the same time, the vehicles are parked adjust to the homes and the engines release all kinds of air pollutants including the volatile organic compounds (VOCs), and the particulate matter (PM), carbon monoxide (CO), oxides of nitrogen (NOx), and sulphur oxides (SOx), which are jointly termed to as Criteria Air Contaminants (CACs). Both the NOx and VOCs supply to the arrangement of the ground- level ozone and this is one of the major components of smog, which is often to be seen as a haze over urban centres.

In the 2000, emissions of the NOx and VOCs from these diesel engines that powered the farming and forestry, construction, mining, machines were equal to those created by about 480, 000 heavy duty diesel trucks and buses and this NOx finds its way to these homes though the open windows.

Figure X below shows the guidelines of nitrogen dioxide exposure over several countries.

Figure X:  Title (National environmental health forum, 1997)


Nitrogen dioxide has shown to be an indoor pollution contaminant that comes from various home cooking, heating appliances and indoor tobacco smoking. It has shown to have an impact on the human’s health with respiratory issues and impairs lung functionalities.  Epidemiological studies have assessed and quantify the health impact of indoor nitrogen dioxide exposure. It has shown a greater impact on the health effect of asthmatics and children. The indoor nitrogen dioxide concentration has been an issue for many countries over past decades. There has been guidelines set for improvements, however, Australia have not met to the guideline standards.


The resolution simply require the assessments to the problem, standard identification, formation of authorities to hold responsible for clean air and actions to improve air quality. At current Australia has National Enforceable Standards for Ambient air (NEPHs), but it only contains non enforceable guidelines for some indoor air pollutants. It is necessary to establish a set of national standard for indoor air quality in the near future. The Australia state government has imposed regulations for outdoor air control legislations which can fine up to $1 million for infringements of air pollution. However, there’s lack of interest for indoor air environment concerns. There have only been occasional involvements to issue information brochures about the gas heaters and the passive smoking to the community.

There should be actions and plans to help reducing the level of indoor air pollutants, such as nitrogen dioxide. Some immediate steps to address the indoor nitrogen issues include:

  • Establish a national body to be responsible for adequate nitrogen dioxide concentration.

Lack of ownership and responsibility to indoor air quality will no doubt be effective. There should be a government department that is to be responsible for unhealthy air quality that affects the community.

  • Develop standards for nitrogen dioxide.

Until Australia has adequate benchmarks, we cannot establish a degree of concern about the level of nitrogen dioxide or any pollutants and its action for resolution. At current, Australia is very slow in developing standards that meet the world’s air pollution standards. The benchmarks should be expanded to all pollutants (not just nitrogen dioxide) and to adopt them into international standards to set as working guidelines.

  • Collate data measured indoor nitrogen dioxide levels into a national database.

Collating indoor air pollution data into a national database allow an easy accessible source to obtain any raw data or measurements. At current, the Commonwealth has began funding for the first project in Australia to gather data to a simplified source. This will establish extensive knowledge hubs which engage data from all over the world.

  • Extensive education to the public about the concern of nitrogen dioxide.

At current, communities are not aware about the health risks posed by nitrogen dioxide pollutant, and only occasionally are attentive to the media. Smoking causes the most indoor air pollution, but the media addresses smoking harms human health, but do not explain indoor smoking can increase the indoor concentration, where if not highly ventilated, then it will be trapped indoor. The information base is not adequate for delivering the objectives.

  • Replace old unflued heaters (especially in NSW schools).

NSW government schools use the most gas heaters, which research shows that the nitrogen dioxide concentration levels goes up to 2. 9ppm. It is estimated that the number of affected students can be up to 50, 000. Replacing the gas heaters can minimize the affected health issues to the students.

  • Establish programs that will address the problems.

Coordinated education program can equip the community with the required knowledge about decisions and actions that could affect the quality of indoor air and nitrogen dioxide. This is necessary if other plans are not feasible and would be an effective method to influence human behaviors and decisions. A recommendation is to action a national day for air quality to increase the community’s awareness.

  • Improve ventilations where sources are presented indoors.

This is the simplest method to reduce levels of indoor air pollution. Increase ventilation will allow emissions from sources to be diluted with the ambient air. Building should have standards to achieve this; therefore, this should be included in building codes and standards.  The vehicles that are parked near the houses should be parked far away from any open windows and doors. So the planners of the house should ensure that when the houses are erected, the parking should be far away from the houses. At the same time, it would be important if the home owners strived to stop using kerosene stoves or other equipments that emits NOx.