Acid Rain

Acid rain

Acid Rain

The term Acid rain or more accurately acid precipitation is commonly used to mean the deposition of acidic components in rain, snow, dew, or dry particles. Acid rain occurs when sulfur dioxide and nitrogen oxides are emitted into the atmosphere, undergo chemical transformations, and are absorbed by water droplets in clouds. The droplets then fall to earth as rain, snow, mist, dry dust, hail, or sleet. This increases the acidity of the soil, and affects the chemical balance of lakes, streams and swimming pools! We have major manufacturing and oil refineries not far from us in Pattaya which contribute to acid rain formation. A little bit of acid rain is actually good for salt water pools as they tend to have a higher pH than chlorine pools. We have to use hydrochloric acid to bring down the pH in these swimming pools. The term “acid rain” is often used more generally to include all forms of acid deposition — both wet deposition, where acidic gases and particles are removed by rain or other precipitation, and dry deposition removal of gases and particles to the Earth’s surface in the absence of precipitation.

Acid precipitation

Acid rain is defined as any type of precipitation with a pH that is unusually low. Dissolved carbon dioxide dissociates to form weak carbonic acid giving a pH of approximately 5.6 at typical atmospheric concentrations of CO2. Therefore a pH of less than 5.6 has sometimes been used as a definition of acid rain. However, natural sources of acidity mean that in remote areas, rain has a pH which is between 4.5 and 5.6 with an average value of 5.0 and so rain with a pH of less than 5 is a more appropriate definition. “Acid rain is a serious environmental problem” Acid rain accelerates weathering in carbonate rocks and accelerates building weathering. You can see the results of accelerated building weathering all around Pattaya and Bangkok. It also contributes to acidification of rivers, streams, and forest damage at high elevations. When the acid builds up in rivers and streams, it can kill fish. It also plays havoc with the water balance of swimming pools as it can bring down the pH to unacceptable levels. I have even felt my eyes stinging whilst being caught out on my motor bike when it starts to rain here in Pattaya, Thailand.

Glacial Ice

Evidence for an increase in the levels of acid rain comes from analyzing layers of glacial ice. These show a sudden decrease in pH from the start of the Industrial Revolution of 6 to 4.5 or 4. Other information has been gathered from studying organisms known as diatoms which inhabit ponds. Over the years these die and are deposited in layers of sediment on the bottoms of the ponds. Diatoms thrive in certain pH levels, so the numbers of diatoms found in sediment layers of increasing depth give an indication of the change in pH over the years.

Since the industrial revolution, emissions of sulphur and nitrogen oxides to the atmosphere have increased. Occasional pH readings of well below 2.4 (the acidity of vinegar) have been reported in industrialized areas. Industrial acid rain is a substantial problem in the People’s Republic of China, Eastern Europe, Russia and areas down-wind from them. These areas all burn sulphur-containing coal to generate heat and electricity. The problem of acid rain not only has increased with population and industrial growth, but has become more widespread. The use of tall smokestacks to reduce local pollution has contributed to the spread of acid rain by releasing gases into regional atmospheric circulation.


Often deposition occurs a considerable distance downwind of the emissions, with mountainous regions tending to receive the most (simply because of their higher rainfall). An example of this effect is the low pH of rain (compared to the local emissions). Acid rain was first found in Manchester, England. In 1852, Robert Angus Smith found the relationship between acid rain and atmospheric pollution. Though acid rain was discovered in 1852, it wasn’t until the late 1960s that scientists began widely observing and studying the phenomenon. Mother Nature also causes acid rain via volcanoes.

Steve Johnson is the Managing Director of “WET” Water Engineered Technologies (Thailand) and offers a broad range of “Commercial & Domestic” water filtration solutions, potable water, plus swimming pool design, construction, equipment and consultation. Steve can be contacted on # 0848 28317 or email

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