Study Says Acid Rain Falls Over San José

June 2, 2006

One in every four rain showers that fall over the nation’s capital can be defined as acid rain, according to a joint study by Universidad Nacional (UNA) and the Municipality of San José.

The “First Annual Acid Rain Report for the City of San José: 2005” analyzes rain samples collected from July to December 2005 at six points in the capital, and reveals that as the rainy season advances, episodes of acid rainfall increase, UNA researcher Jorge Herrera told journalists during a recent presentation of the study results.

While getting caught in an acid rain shower may not bring about immediate illness, risks to human health are created by continued exposure to the toxic gases that produce acid rain (from car exhaust pipes and industry smokestacks), Herrera explained.

Acid rainfall mixing with potable water systems could also lead to problems, he said.

In nature, the acidification of rivers and lakes can cause fish and microorganisms to die. Also, acid rain has a harmful effect on forests and can increase the acidity of farmland, diminishing its productivity, Herrera warned at his May 19 presentation.

So far, the effects of acid rain can be seen on a global scale mainly in the damage it produces to infrastructure, he added. Acid rain accelerates corrosion of buildings, statues and paintings, leaving irreparable damage to structures that may have cultural or historical significance. Structures built from limestone, sandstone and marble tend to corrode at a faster rate than others, according to Herrera.

Acid rain results when toxic gases expelled in cities and industrial areas alter the properties of rain, which commonly registers a natural acidity of 5.0 pH units in uncontaminated environments. Acid rain is defined by values of less than 5.0.

Although San José registers pH averages between 5.20 and 5.30, one in four rain showers register below 5.0, the report revealed.

PH values recorded in the capital ranged from 4.30 at the Public Security Ministry, in southeastern San José, to 6.80 at Barrio Cuba, in southwestern San José. Other sites where samples were taken are the Children’s Museum, the Public Library, the San JoséMunicipality and the Costa Rican Electricity Institute (ICE) in Pavas, in western San José.

“Our problem is that we have episodes of acid rain. Thank God it’s not a general problem, but we do have a problem,” said Herrera, who compared San José’s average pH to that of other cities.

The city of Sao Paulo, Brazil, registers a very low pH of 2.70, while Mexico City has a pH of 4.7. Certain cities in the eastern United States show average values of 4.8, while Canada’s average of 4.25 is comparable to Costa Rica, the expert said.

Too Many Vehicles?

Sulfur dioxide (SO2) and nitrogen dioxide (NO2) are the main gases causing acid rain, which can be viewed as an atmospheric cleaning mechanism, Herrera said. Fuel combustion in vehicles and industrial smokestacks are the main producers of sulfur dioxide, although acid rain can also develop through natural processes.

For example, acid rain in the areas surrounding Poás Volcano, in the province of Alajuela, and Irazú Volcano, east of San José, is brought about by volcanic emissions, affecting nearby forests whose trees lose their leaves, said Alberto Salas, biodiversity coordinator for the San José-based World Conservation Union (IUCN) regional office for Mesoamérica.

However, in San José, the problem stems from different issues. “(Costa Rica) has not been very careful about (regulating) the amount of sulfur in fuel,” Herrera said, adding that controlling the amount of sulfur in fuel and driving environmentally friendly vehicles, such as hybrid cars, could help.

According to government officials, approximately 1.2 million cars and trucks are registered in the country; of those, 70% are in the greater metropolitan area.

Olman Segura, dean of Universidad Nacional, listed the increasing number of vehicles on San José’s streets, their poor conditions, organizational problems with public transportation, population density and a lack of awareness among residents as the causes for the city’s decaying air quality.Maureen Clark, Vice-Mayor of San José, highlighted the importance of reducing San José traffic.

“We need to improve our vehicles and diminish their numbers downtown,” Clark said. “Traveling on foot would be ideal for this city.”

She said approximately 80% of people who enter downtown San José do so by bus, while only 20% drive their own vehicles. The acid rain study was conducted within the framework of a research project by UNA and the San JoséMunicipality called “Green Agenda Program: San José,” which seeks to develop environmental quality indicators for San José.

The project started in 2003 with a system to monitor air pollution in the city; it was expanded to include acid rain in 2005. The university and municipality plan to conduct annual acid-rain studies, Herrera said.

UNA dean Segura mentioned that as part of the activities planned for June, Environment Month, UNA and the HerediaMunicipality plan to announce the results of the first air-quality study for the city of Heredia, north of San José.

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