Silver Iodide Research Paper

Austin Meng

Rogers

Honors Chemistry

04 November 2014

Honors Chemistry Literature Review Rough Draft

Around this time of the year, there are many ski resorts that will begin to open their services soon. However, what happens when there isn’t enough “natural” snow for everyone to have a good time? Often times, these ski resorts will utilize silver iodide to produce artificial precipitation, so that they do not shut down, lose business, etc. However, using such a chemical will naturally pose this question concerning the surrounding environment: How does silver iodide affect its surrounding environment when used to modify natural weather courses and phenomenons?

The implementation of silver iodide into the atmosphere is not restricted or limited

to the sole purpose of commercial business in ski resorts. It goes to certain extents as to varying certain natural phenomenons to produce more precipitation in particularly dry locations. Bruintjes (1999) defines “the introduction of any substance into clouds for the purpose of changing them is called cloud seeding.” According to Battan (2014), Cloud seeding is often performed through ground generators, airplanes, and even projectiles such as in an experiment by Soviet scientists. Despite the method to get the chemical into the cloud, cloud seeding will generally work as the solution will disperse a large number of ice nuclei which then lowers the surrounding overall temperature in which the solution was released.
The effects are not always distinct and available to the naked eye, but the use of silver iodide into the atmosphere does produce certain effects and even consequences. One study according to Ćurić, Janc, and Vučković (2007) finds, “the main consequence of hail cloud seeding is the additional cloud ice production by different nucleation mechanisms”. This will happen if the objective goal is not reached. This “goal” is to reduce hail as a result of cloud seeding. Changes in rates by which hail “accretes cloud water in dry growth regime and snow accretes rain”, according to Ćurić, Janc, and Vučković (2007), contributed largely to hail reduction at the surface. A separate study by Guo, Zheng,and Jin (2005) demonstrating the differences between silver iodide and liquid carbon dioxide show that the “accumulated precipitation at the surface can be increased and redistributed, and more concentrated in the downstream region of seeded clouds”. Both studies depict the positive effects in that silver iodide is very effective in increasing precipitation, as well as decreasing the potential outcome of harmful, natural weather phenomena.
In a study conducted in Israel, cloud seeding had been in action for many decades, starting as early as the 50s. However, the study shows that the ratio of rainfall in uneven, hilly terrain compared to the rainfall in the plains decreased in the 60s and 70s in comparison to the higher rates in the 50s. This finding demonstrates an increase of air pollution that has caused precipitation as a whole to decrease. However, recently found by Givati and Rosenfield (2005), “the opposite effects of air pollution and seeding appear to have nearly canceled each other in recent years, leading to the false impression that cloud seeding is no longer effective”. Seeding seems to also, then, have a reverse effect of decreasing precipitation if it were to cease.
One may pose the question, “Why does silver iodide produce these certain effects”?

Arlen Huggins answers in an interview conducted by Moseman (2009), “One thing people discovered early on is that the structure is very similar to that of ice. The lattice structure at the molecular level is very, very close”. Therefore, the silver iodide, in a way, “tricks” the atmosphere into producing excessive precipitation as a result of a release of silver iodide. The similar molecular structure proves to show its extreme effects as Huggins states in Moseman’s interview (2009), “If you had a large basin like I work with, between 300,000 and 500,000 acre-feet*, a 10 percent increase would equal 30,000 to 50,000 more acre-feet of water. If you can do that, it's very economically sound”. After the utilization of such a chemical, water/precipitation could be stored, saved, filtered, distributed, etc., and perhaps, it could help locations that are lacking in water. This does bring up suspicions of inserting a foreign object into the air, as Moseman (2009) writes, “As a pollutant, silver iodide is almost overshadowed by smokestacks spewing kilotons of pollution, or by auto exhaust”. Therefore, while being a “pollutant” by certain definitions, the silver iodide is a chemical that is not particularly harmful to the surrounding atmosphere or the people living in the area beneath. While a single chemical could not entirely resolve conflicts of droughts, it will very likely aid in the preservation

of water in the case of potential water shortage conflicts.
In conclusion, silver iodide produces many positive effects, such as reducing hail, increasing precipitation, providing rain for preservation in case of droughts, and even reducing certain harmful pollutants. While it is still being experimented with, silver iodide works in this way because of its almost identical molecular composition in comparison to ice. The chemical is still questionable as particular, specific results are not easily determined. It is not entirely certain if the larger production of snow, hail, or rain was a direct effect of the silver iodide, and it is also uncertain concerning the exact amount that the silver iodide is responsible for. If silver iodide is released into the air for the purpose of cloud seeding, then an excess/additional amount of precipitation will result because of the chemical’s similar structure to ice. This hypothesis may be testable in certain settings such as laboratories or projections.

Bibliography

Battan, L.

(2014, February 20). Weather modification. Retrieved from http://britannica.com/EBchecked/topic/638346/weather-modification

Bruintjes, R. (May 1999) . “A Review of Cloud Seeding Experiments to Enhance Precipitation and Some New Prospects”. Retrieved from: http://journals.ametsoc.org/doi/abs/10.1175/1520-0477(1999)080%3C0805:AROCSE%3E2.0.CO;2

Ćurić, M., Janc, D., Vučković V. (2007, February 1). Cloud seeding impact on precipitation as revealed by cloud-resolving mesoscale model. Retrieved from http://link.springer.com/article/10.1007/s00703-006-0202-y#page-1

Guo, X., Zheng, G., Jin, D. (2005, April 5). A numerical comparison study of cloud seeding by silver iodide and liquid carbon dioxide. Retrieved from http://www.sciencedirect.com/science/article/pii/S0169809505001420

Givati, A., Rosenfield, D. (2005). Separation between Cloud-Seeding and Air-Pollution Effects. Retrieved from http://journals.ametsoc.org/doi/abs/10.1175/JAM2276.1

Moseman, Andrew (2009, February 19) . “Does cloud seeding work?” Retrieved from

http://www.scientificamerican.com/article/cloud-seeding-china-snow