Sierra Nature Notes, Volume 1, November 2001

Continued from:
Understanding Smog in the Sierra
by E. F. van Mantgem

III. Your Lungs as a Sponge: Why You Should Care about Air Pollution

Ozone at Two Levels
High concentrations of the wrong air ingredients are universally recognized as air pollution. Perhaps the most widely publicized of these air pollutants is ozone (O3). Normally found in the upper stratosphere, guarding the earth's surface from harmful ultraviolet (UV) radiation, ozone is now found in abnormal quantities in the ground level atmosphere. Normally a volatile, quickly dissipated molecule, high concentrations persist because of our continuous, heavy use of fossil fuels. Ambient ozone damages plants and agricultural crops, in addition to harming humans. For lungs everywhere, ground level ozone breaks down the mucosal barrier between gas and liquid, resulting in a damaged lung lining and a compromised immune system.

Ponderosa Pine damaged by air pollution in southern Sierra. Note thin foliage on left tree compared to healthier tree on right.

Because the formation of ozone requires sunlight, warm and sunny places with varied topographies like California have the highest average levels of ambient ozone in the country. Sierran locations above 6,000 ft. aren't significantly impacted, but lower elevation ponderosa pine and Jeffrey pine forests show dramatic mottling in their needles. This compromises the plant's ability to grow by diminishing its photosynthetic capabilities.

During the growing season of 1997, monitoring stations in the Sierra region recorded high ozone measures of 120 ppb-hr (parts per billion averaged per minute per hour). Compare this to the chilly Northwest and to flat Florida, each with an average less than five ppb-hr during the same year. Although federal health standards list 120 ppb-hr as the maximum acceptable level and California lists 90 ppb-hr as the state standard (Table 1), researchers have found that damage to vegetation starts with ambient ozone levels as low as 60ppb-hr. Studies also show that in young, elderly, and other sensitive humans, long-term healthy levels of ozone exposure should be no higher than 20-25 ppb-hr.

Ironically, while ground level ozone increases, the stratospheric protective ozone shell found between 10-25 miles above the earth's surface is thinning. It has been estimated that the global incidences of skin cancer, cataracts, and infections will increase by as much as 15% with just a 7% decline in the stratospheric ozone layer. This is the result of the infamous chlorofluorocarbons (CFC's) that are commercially produced and released with the use of spray cans, air conditioners, and refrigerators. The CFC's that make it to the stratosphere interfere with the fragile balance of ozone produced when UV rays split oxygen molecules. The UV light splits CFC's, forming chlorine and bromine, which in turn react with the dilute ozone layer, weakening its potency against short wave penetration.

Acid "Rain", Both Wet & Dry
Another commonly known, man-made pollutant is "acid rain", a generic term for both wet and dry acid deposition in the environment. The name "Acid rain" would be more technically accurate if it was changed to "Multiple Reactions of Nitrogen and Sulfur, Two Naturally Occurring Gaseous Elements" but this is too much to say. Now these elements exceed healthy levels in our air, as both volatile and persistent acid compounds.

Due to the burning of fossil fuels (coal, gasoline, etc.), these two elements are being released into the atmosphere disproportionately, providing fodder for billions of tiny, sun activated, chemical reactions. The toxic products of these reactions include ozone, as well as sulfure dioxide (SO2), nitrous oxide (NO2), nitric acid, and fine, particulate matter. The products are then dispersed and pocketed by weather, moisture, rain, and wind patterns.

Monitoring consistently shows that nitrogen compounds (NOx's) are the major component of acid deposition in the Sierra. NOx deposition acidifies sensitive, alpine lakes and creates concentrated acidic pulses in the mountains with the late summer rains and springtime Sierra snowmelts. Many wildlife biologists are currently investigating the suspicion that these acidic pulses are decimating the Sierra mountain-yellow legged frog population. The frogs were everywhere 15 years ago, but now they're in tiny isolated pockets. Coincidentally, the high elevation lakes in which they're still living seem to sustain relatively little exposure to air pollution from the west side of the Sierra crest, the source side for airborne NOx's.

Wherever acid rain goes, there is damage. Acid deposition, wet and dry, contributes to the death of plants by altering biochemical processes, water and soil pH. Acid rain causes rubber and building materials to decay at a faster rate, including historical buildings, statues, and monuments. The loss of scenic viewing has also been well documented as a result of the airborne, acid rain precursors (i.e. NOx's & SOx's). The inhalation of fine SO2 and NO2 particles are positively correlated with an increase in premature death from both heart and lung complications.

Statistically, the regions in the U.S. with significantly higher acid deposition rates are the coal-burning regions, like the northeast and the upper mid-west. Unfortunately, this is just a relative statistic. Even with much lower levels of acid deposition in the west, the sensitive lakes and streams in the Sierra Nevada are so poorly buffered against even the mildest of acidic pulses that the local flora, fauna, and geologic processes may still be altered over time. This inability of Sierran aquatic systems to cope with mild acid pulses is due to regional characteristics: thinner topsoils, granite subsurface layers, less vegetation, steeper slopes and a dry climate.

Particulates Matter
A final, more intuitively recognized air pollutant is particulate matter (PM). PM includes solid and liquid particles, with the exception of pure water molecules. All alone, one PM particle is usually impossible to see, but in high concentrations, these particles can appear as opaque chemical clouds, fog, smoke, or haze. As described earlier, acid rain contributes to PM in the form of fine SO2 and NO2 particles, but soot, ash, dust, molds, pollens, and other coarse particles are the popularly known constituents.

Within the U.S., California has a relatively high level of particulate pollution (PM). This is attributed to the dry climate, the fire regime, and the intensive agriculture practices in the region. In the Central Valley of California, plowing, discing, and other agriculture activities routinely cause soil to be airborne as dust. Wildfires, prescribed fires, agricultural fires, and wood stove fires all generate smoke, ash and soot. Industry emits volatile plumes of sulfur dioxide, nitrogen oxide, and organic carbons, all of which may glom onto or react with other atmospheric chemicals and particles. As everyone knows, Californians like to drive, and populated areas and roadways are a source of emissions from cars and trucks, as well as more dust when roadways are unpaved.

One aesthetically valuable aspect of the environment lost through PM pollution is visibility. Scenic views are completely obliterated when airborne PM particles scatter and absorb light, obscuring the clarity and color of whatever is in front of you. As we've all experienced, it's hard to enjoy a visit to places like Mt. Whitney, Half-Dome, or Moro Rock when you can't see. As a result of PM pollution, scenic viewsheds are considered to be a valuable but endangered, national human resource. Continued