Haze is the suspension in dry particles of salt, aerosols, dust, or photochemical smog atmosphere, which are so small (having the diameters 0.1 microns [0.00001 cm]) that they cannot be individually felt or seen with the naked eye. However, the aggregate reduces horizontal visibility and provides the atmosphere with an opalescent appearance. Haze appears as a yellowish or bluish veil based on whether the background is light or dark, respectively. In reference to these colours, the haze is discriminated against by the mist, which gives the sky a greyish cast.
Haze often takes place, when the smoke and dust particles accumulate in dry air, relatively. Whenever the weather conditions block the dispersal of smoke and other pollutants, they can concentrate and produce a normally low-hanging shroud, that impairs visibility. They can also become a respiratory health threat. Industrial pollution can also result in a dense haze, which is also called smog.
Haze has been a particularly acute problem since 1991 in Southeast Asia. The primary source of haze has been fired occurring in Borneo and Sumatra. In response to the Southeast Asian haze in1997, the ASEAN countries agreed on a Regional Haze Action Plan in the same year. But, in 2002, all the ASEAN countries signed the Transboundary Haze Pollution Agreement. However, pollution is still a problem today. Under this agreement, the ASEAN secretariat hosts a support and coordination unit. During the Southeast Asian haze in 2013, Singapore experienced a record level of high pollution, with the 3-hour Pollution Standards Index reaching a record level as high as 401.
In the United States, the IMPROVE (Interagency Monitoring of Protected Visual Environments) program has been developed as a collaborative effort between the National Park Service and the US EPA to establish the chemical composition of haze in the National Parks and establish air pollution control measures to restore the visibility to the pre-industrial levels. In addition, the Clean Air Act needs that any current visibility problems be remedied, and the problems of future visibility are prevented, in 156 Class I Federal areas located in the entire United States.
Haze is no longer considered a domestic problem. It has become the cause of international disputes among the neighbouring countries. Haze also migrates to the adjacent countries and thereby pollutes other countries too. One of the most recent problems takes place in Southeast Asia, which largely affects the Malaysia, Indonesia, and Singapore nations. In 2013, because of the forest fires in Kuala Lumpur, Indonesia and the surrounding areas became shrouded in a pall of noxious fumes, smelling of coal and ash for more than one whole week, in the country’s worst environmental crisis from 1997.
Sumatra Island of Indonesia, Riau, and the Indonesian regions of Borneo, where plantation owners, fishermen, and miners set hundreds of fires in the forests for land clearing at the time of dry weather, are the primary causes of haze. Also, winds blow the most fumes across the narrow Strait of Malacca to Malaysia, though Indonesia parts are also affected. The 2015 Southeast Asian haze was the other major crisis, although there were occasions like 2006. And, 2019 haze which was less impactful compared to the three major Southeast Asian haze of 1997, 2013, 2015.
Haze causes issues in the terrestrial photography area, where the penetration of huge amounts of dense atmosphere can be necessary to image distant subjects. And, this also makes the visual effect of a contrast loss in the subject, due to the reason, the effect of light scattering through the haze particles. For such reasons, the colours of sunrise and sunset appear subdued on hazy days, and stars can be obscured at night. In some other cases, attenuation by haze is much greater than, toward sunset, the sun has disappeared altogether before reaching the horizon.
Haze is described as an aerial form of the Tyndall effect; thus unlike other atmospheric effects like fog and cloud, haze is spectrally selective: shorter (which are blue) wavelengths are scattered more, and longer (either red or infrared) wavelengths are scattered less. Because of this reason, several super-telephoto lenses often incorporate coatings or yellow filters to enhance image contrast. Infrared (IR) imaging can also be used to penetrate haze over a long distance, with a combination of IR-sensitive detectors and IR-pass optical filters.
Formation of Haze
In general, the industry is a primary source of particulate matter. Industries like steel, cement, and power generation create massive amounts of particulate matter (PM2.5) in the course of their regular operations. These particular emissions are controlled by the use of a dust collection system (which are called baghouse). These specific systems suck up the dust-laden air or fugitive dust and send it through a fabric filter (which is called a baghouse filter), which traps the dust particles, but they allow the air to pass through.