User:Snead.Emily/Emily Snead Sandbox

Aerosol Brown Cloud
Aerosol Brown Clouds are atmospheric phenomena where suspended solid and liquid pollutants condense in the troposphere to form a characteristic brown haze. Aerosol pollutants originate from human activities as well as natural earth processes. Formed in regions of high industrial activity and air pollution output, Aerosol Brown Clouds have direct adverse effects on climate. Aerosol Brown Clouds are prevalent in east Asia, south Asia, Indonesia, southern Africa, and the Amazon Basin in South America.

Origin of Aerosol Pollutants
Aerosol Brown Clouds are characteristically brown in color because of the distinct spectral and chemical properties of natural and anthropogenic aerosols present. Aerosols including fly ash, dust, black carbon, sulfur dioxide, nitrogen oxide, and volatile organic compounds are produced during fossil fuel and biomass burning. Additional human activities including trash incineration, slash & burn agriculture, and industrial combustion (coal & wood burning) produce high amounts of air pollutants that alter the characteristics of cloud formation and precipitation. Anthropogenic aerosols are difficult to quantify because of their small effective radii and chemical interactions with other atmospheric aerosols in Brown Clouds.

Common earth processes produce natural aerosols. Desertification and erosion of dry lake beds and plains emit large amounts of dust, a coarse-grained aerosol. Categorized as short-term events, volcanic and hydrothermal activities emit sulfur dioxide into the atmosphere and is easily transported by trade winds on a global scale. During rough wave and high wind conditions, coarse-grained salt particles from the ocean are precipitated into the atmosphere, contributing to the influence of cloud formation. Natural aerosols are easily identifiable by remote sensing and in situ instruments because of their large effective radii.

Aerosol Regulation
The United States, Canada, and many countries throughout Europe have strict regulations involving air pollution. However, many developing industrial countries in Asia and South America have poor pollution regulations. For example in China, rapid economic and industrial expansion combined with loose emission regulation has led to exponential increases in anthropogenic aerosol production. During dry winter months the Asian Brown Cloud is most prevalent throughout China and India due to increased residential coal and wood burning.

Because of their chemical and physical compositions aerosols are difficult to quantify, leading to further challenges in governmental regulation. Brown Clouds have serious ecological and biological health effects, and emissions throughout developing industrial countries are expected to increase if strict pollution regulations are not imposed.

Influences on Cloud Formation
When clouds form, water vapor in the atmosphere condenses around hygroscopic nuclei originating from natural and anthropogenic aerosols. When anthropogenic aerosols are abundant in the troposphere, they attract high amounts of small water droplets. The water droplets that condense around these aerosols have minute effective radii, thus prompting the formation of haze. Aerosols within the haze prohibit condensing water droplets from growing large enough to reach a precipitation state, and therefore influence rainfall patterns in regions affected. Brown Clouds typically have greater effects than haze because of their industrial-centered locations and high concentrations of anthropogenic aerosols with degenerative health effects.

Aerosol Brown Clouds form under certain atmospheric and terrestrial conditions. High mean temperatures, low winds, high solar radiation, and low mean precipitation are atmospheric conditions that promote Brown Cloud formation. Terrestrial characteristics including relatively flat regions, valleys, and low-lying coastal regions surrounded by mountains also promote Brown Cloud formation. Aerosol Brown Clouds occur frequently where these terrestrial and atmospheric conditions coincide with highly industrialized zones with high pollution output.

Influences on Precipitation
Aerosol Brown Clouds reduce regional rainfall because aerosols act as cloud-condensing nuclei. The haze reduces surface solar radiation, which decreases net sea evaporation. Water evaporated from oceans is the greatest source of water vapor for cloud formation, and its decrease because of Brown Cloud formation limits the amount of water available for precipitation. Black carbon in Aerosol Brown Clouds absorbs solar radiation and contributes to decreases in cloud development because of its influences on temperature inversions. Temperature inversions imply stable atmospheric conditions where warm air overlies cooler air, resulting in trapped aerosol pollutants close to ground surfaces. The minute effective radii of water droplets within Brown Clouds combined with the inability to develop into large droplets, inhibits net precipitation. Because of their small size, Aerosols contained within Brown Clouds extend the overall lifespan of the haze, resulting in magnified ecological and climatic effects over affected regions.

Recent Studies
In 2006, a study by Auffhammer et al. identified a reduction in rice harvest productivity in India due to decreased precipitation and increased atmospheric dimming as a result of the Asian Brown Cloud. Caused by aerosol nucleation in Brown Clouds, atmospheric dimming reduces available light for photosynthesis and hinders visibility. Results from this study indicate a correlation between decreased rice harvests and an increase of Brown Clouds. The study also noted a 6-17% reduction in rice yields during the test period. Rice harvest yields in India have leveled off despite growing demands due to Brown Cloud formations, and have serious implications on future food shortages.

In 2003, Ramanathan et al. identified a shift in the monsoonal cycle over China due to the Asian Brown Cloud. Over time, the monsoon has shifted southwards, causing yearly droughts in Northern China and flooding in Southern China. The Asian Brown Cloud disrupts monsoonal circulation because it causes temperature inversions that hinder convective mixing. A 2006 study by Huang et al. discovered that the monsoonal drift is also due to negative forcing (cooling) properties of aerosols on ground surfaces. Models used in the study consider the long lifespan and small effective radii of water droplets in Aerosol Brown Clouds that reduce net precipitation.