What does haze weather mean?
Haze is an atmospheric phenomenon where visibility of the sky is reduced due to the high presence of smoke, dust and other airborne particles, giving the sky a bluish or brownish color. According to the World Meteorological Organization, horizontal obscurations can be classified among fog, ice fog, steam fog, mist, haze, smoke, volcanic ash, dust, sand or snow.
The coefficient of haze, which is also known as smoke shade, is a measurement of visibility interference in the atmosphere and it is calculated by the absorbance formula: COH = log10 (I1 / I0).
However, haze is usually measured using the Pollutant Standards Index (or PSI), which is a type of air quality index that indicates the level of pollutants in the air. It may differ depending on the country since other indices are used worldwide, such as Air Quality Health Index or Air Pollution Index. Some examples of countries using PSI as an indicator of air quality are the United States (until 1999, when it was changed for Air Quality Index) and Singapore.
Singapore’s National Environmental Agency (NEA), indicate PSI with a number between 0 and 500. If air quality reaches levels over 100 PSI, population may notice it and can suffer health effects. As a point of interest, Singapore has the 3-hour PSI reading record with 401 (21st June 2013).
Causes and effects of haze
Haze particles emissions come from sources such as farming (ploughing in dry weather), traffic, industry, and wildfires. Cars combustion engines or industrial pollution emit sulfur dioxide particles (SO2) that generate haze, which after chemically reacting in the atmosphere with other compounds can become smog or acid rain.
Wind can carry haze from one country to another, like what happened in Malaysia in 2013. Despite Arctic has not enough emissions to pollute its own air, during springtime that region suffer a reddish-brown haze due to air pollution emissions mainly coming from Asia. The most characteristic feature of Arctic haze is the ability of its chemical ingredients to persist in the atmosphere for an extended period of time, in comparison with other pollutants.
In Indonesia it is typical to burn trash because of the lack of cleaning services, or plantations, in order to clean land during dry weather. Especially in the islands of Sumatra, Kalimantan and Riau, fires are more regular, what made these places main sources of haze.
In 2013, due to indonesian forest fires, Kuala Lumpur (Malaysia’s capital) suffered extreme haze weather conditions. As Indonesia is considered the world’s third largest greenhouse gas emitter, in 2014 after what happened with Malaysia it also became part of ASEAN Agreement.
Other laws or agreements to preserve the environment and solve visibility problems are: the Interagency Monitoring of Protected Visual Environments (IMPROVE) program as a collaboration between US EPA and the National Park Service, or the Clean Air Act also implemented by US Environmental Protection Agency (EPA).
In order to reduce haze pollution in Southeast Asia, the Association of Southeast Asian Nations signed in 2002 an environmental agreement. In 2014 this agreement was ratified. Member states of the agreement are: Malaysia, Singapore, Brunei, Myanmar, Vietnam, Thailand, Laos, Cambodia, Philippines and Indonesia.
What is the difference between haze, fog and mist?
The three of them imply reduced visibility because of weather conditions (for fog and mist) or air pollution (for haze). This is the main difference, while fog and mist are formed by the suspension of water droplets, haze is made of extremely small and dry airborne particles.
Fog is the name given to resulting visibility of less than 1 km, according to the international agreement for aviation purposes. However, in weather forecasts for the general public it is understood as less than 180 meters of visibility. On the other hand, mist is exactly the same phenomenon as fog lowing its density and increasing visibility to 1 km or more.