y the 1980s, sulfur dioxide concentrations in the month of January, when heating demands were at their height, could average more than 75 parts per billion (ppb), nearly double what the U.S. Environmental Protection Agency considers the highest acceptable level. During the same period the average annual nitrogen dioxide concentration was 25 ppb, slightly above acceptable levels.
But the killers, literally, were the particulate emissions -- the fine particles of soot and dust, less than a quarter the diameter of a human hair -- that were released into the air. Photographer Antonin Kratochvil still recalls the haze of soot that used to hang in the Most basin, the surgical masks children wore on their way to school. Among the shades of "Kafka gray," as he puts it, that characterized Czechoslovakia under Soviet rule, the Most basin was the darkest.
The EPA requires that over the course of a year, particulate emission densities not average more than 40 micrograms per cubic meter. In 1980, densities in the Black Triangle averaged more than three times that, reaching nearly 200 micrograms per cubic meter during the winter months.
In a single generation, the average Czech life expectancy had fallen to seven years lower than that of Western Europe. The infant mortality rate was 40 percent higher than the European norm. The incidence of respiratory infections was five times greater. Those who could moved away, a migration caused not by war or natural disaster but by an environment made uninhabitable.
Once released into the air, sulfur dioxide and nitrogen dioxide, which do so much damage to the human respiratory system, undergo a chemical change. With sunlight as a catalyst, they combine with atmospheric water vapor and oxygen to form sulfuric and nitric acids. In a high mountain forest such as the Kruné hory, leaves soak in the acidic moisture from low clouds and mist. When it rains or snows, the acidic precipitation acidifies the soil. Nutrients in the soil get broken down and washed away. In their place substances toxic to trees, such as aluminum, are released and the trees, being the efficient hydraulic systems that they are, suck them up. Between 1972 and 1989 about half of the Kruné hory forests died, 115 square miles' worth, and had to be clearcut.
Ducking into my car to find some refuge from the day's rain, Rock explains that his studies of the effects of acid rain in the northeastern United States were what brought him to the Czech Republic. As a research scientist at the government's Jet Propulsion Laboratory in Pasadena, California, Rock had considered using satellites for environmental monitoring. When he came to the University of New Hampshire in 1987, Rock began trying to assess the decline of New England forests. What he concluded immediately was that airborne pollution appeared to hang in a layer at 3,000 feet, the altitude at which the bottoms of clouds flatten out.
"What I was seeing was that the bottom of a cloud could have a pH of 2.5 while the top of the cloud could be 4 to 4.5."
This is not a trivial difference. Each unit increment on the pH scale indicates a tenfold difference in the concentration of hydrogen ions. The lower the pH, the higher the acidity. What Rock was recording was a pH 100 times lower at the base of the clouds than at their top. Pure water has a neutral pH of 7. Normal rain, because of dissolved carbon dioxide, has a pH of 5.5. Rain is considered acidic when the pH level drops to 4. At 3,000 feet Rock was measuring vinegar. He tells me that in one Vermont forest, on September 20, 1988, scientists measured a single cloud with a pH of 2.6. "For three hours it hung there and just toasted the needles."
Rock concluded that pollution damage hits first and hardest at 3,000 feet, though other researchers questioned this. "I was asked whether this 3,000-foot acid rain damage applied only in a specific location in Vermont where the pollution input was constant. I had to find a place where, at 3,000 feet, they had a range of pollution levels," depending on proximity to industrial sources and wind direction.
"So I came to the Kruné hory. When I looked at the Landsat images I couldn't believe what I saw. The damage was appalling."
This was in 1989. What Rock found on the ground when he arrived in May of that year confirmed the worst.
"Retention of needles is a key indicator of health in these trees. A healthy tree may have 12 or more years of needles on its limbs. These had only two or three. The trees were skeletons with tufts of needles. When I looked at the cells of these needles I saw they were suffering plasmolysis, the inability to retain water. The cell content pulls away from the cell wall. The cells become physiologically crippled."
When Rock takes out photographs of damaged needle cells they recall for me comparisons between normal lungs and smokers' lungs. The cells' chloroplasts, which are responsible for photosynthesis, disintegrate. Acidic tannins, looking like tar, accumulate inside the cell. The cell's walls go flaccid and the needles' normally orderly interior structure disintegrates. Says Rock, "Sulfur dioxide and ozone are the only things that do this."
As it turned out, the most damaged Czech forests were those located at 3,000 feet.