HAZE
Haze is traditionally an atmospheric phenomenon where dust, smoke and other dry particles obscure the clarity of the sky. The World Meteorological Organization manual of codes includes a classification of horizontal obscuration into categories of fog, ice fog, steam fog, mist, haze, smoke, volcanic ash, dust, sand and snow. Sources for haze particles include farming (ploughing in dry weather), traffic, industry, and wildfires.
Haze often occurs when dust and smoke particles accumulate in relatively dry air. When weather conditions block the dispersal of smoke and other pollutants they concentrate and form a usually low-hanging shroud that impairs visibility and may become a respiratory health threat. Haze particles can affect the heart and lungs, especially in people who already have chronic heart or lung disease e.g. asthma, chronic obstructive pulmonary disease (COPD), or heart failure. There may be up to 1-3 days of time between exposure to haze and health effects symptoms.
The health impact of haze is dependent on one’s health status, the PSI level, and the length and intensity of outdoor activity. Reducing outdoor activities and physical exertion can help limit the ill effects from haze exposure. Given the air quality forecast for the next 24 hours, everyone can continue with normal activities. Persons who are not feeling well, especially the elderly and children, and those with chronic heart or lung conditions, should seek medical attention.
Haze is traditionally an atmospheric phenomenon where dust, smoke and other dry particles obscure the clarity of the sky. The World Meteorological Organization manual of codes includes a classification of horizontal obscuration into categories of fog, ice fog, steam fog, mist, haze, smoke, volcanic ash, dust, sand and snow. Sources for haze particles include farming (ploughing in dry weather), traffic, industry, and wildfires.
Haze often occurs when dust and smoke particles accumulate in relatively dry air. When weather conditions block the dispersal of smoke and other pollutants they concentrate and form a usually low-hanging shroud that impairs visibility and may become a respiratory health threat. Haze particles can affect the heart and lungs, especially in people who already have chronic heart or lung disease e.g. asthma, chronic obstructive pulmonary disease (COPD), or heart failure. There may be up to 1-3 days of time between exposure to haze and health effects symptoms.
The health impact of haze is dependent on one’s health status, the PSI level, and the length and intensity of outdoor activity. Reducing outdoor activities and physical exertion can help limit the ill effects from haze exposure. Given the air quality forecast for the next 24 hours, everyone can continue with normal activities. Persons who are not feeling well, especially the elderly and children, and those with chronic heart or lung conditions, should seek medical attention.
CLOUD SEEDING
Cloud seeding is often used as a method to overcome the hazardous haze. Even in areas with very low humidity, there's at least some water in the sky and clouds. A rainstorm happens after moisture collects around naturally occurring particles in the air, causing the air to reach a level of saturation at which point it can no longer hold in that moisture. Cloud seeding essentially helps that process along, providing additional "nuclei" around which water condenses. These nuclei can be salts, calcium chloride, dry ice or silver iodide, which the Chinese use. Silver iodide is effective because its form is similar to ice crystals. Calcium chloride is often used in warm or tropical areas.
There are three cloud seeding methods: static, dynamic and hygroscopic.
Cloud seeding is often used as a method to overcome the hazardous haze. Even in areas with very low humidity, there's at least some water in the sky and clouds. A rainstorm happens after moisture collects around naturally occurring particles in the air, causing the air to reach a level of saturation at which point it can no longer hold in that moisture. Cloud seeding essentially helps that process along, providing additional "nuclei" around which water condenses. These nuclei can be salts, calcium chloride, dry ice or silver iodide, which the Chinese use. Silver iodide is effective because its form is similar to ice crystals. Calcium chloride is often used in warm or tropical areas.
There are three cloud seeding methods: static, dynamic and hygroscopic.
- Static cloud seeding involves spreading a chemical like silver iodide into clouds. The silver iodide provides a crystal around which moisture can condense. The moisture is already present in the clouds, but silver iodide essentially makes rain clouds more effective at dispensing their water.
- Dynamic cloud seeding aims to boost vertical air currents, which encourages more water to pass through the clouds, translating into more rain [source: Cotton]. Up to 100 times more ice crystals are used in dynamic cloud seeding than in the static method. The process is considered more complex than static clouding seeding because it depends on a sequence of events working properly. Dr. William R. Cotton, a professor of atmospheric science at Colorado State University, and other researchers break down dynamic cloud seeding into 11 separate stages. An unexpected outcome in one stage could ruin the entire process, making the technique less dependable than static cloud seeding.
- Hygroscopic cloud seeding disperses salts through flares or explosives in the lower portions of clouds. The salts grow in size as water joins with them. In his report on cloud seeding, Cotton says that hygroscopic cloud seeding holds much promise, but requires further research.