Much of the ozone pollution at high elevations in the mountains of Western North Carolina is transported by winds from other states. The results from the high elevation ozone monitoring site near Shining Rock Wilderness figure above show ozone concentrations do not change throughout the day and that average concentrations are greater than at the Bent Creek site.
Consequently, people and vegetation at higher elevations are exposed to more ozone then people and vegetation at low elevations.
Ozone effects on plants are most pronounced when soil moisture and nutrients are adequate and ozone concentrations are high. Under good soil moisture and nutrient conditions the ozone will enter through openings into the leaf and damage the cells that produce the food for the plants. Once the ozone is absorbed into the leaf, some plants spend energy to produce bio-chemicals that can neutralize a toxic effect from the ozone. The presence of ozone in an area can be detected when consistent and known symptoms are observed on the upper-leaf surface of a sensitive plant species.
The photograph to the right shows the severe reddening of the blackberry foliage near Shining Rock Wilderness in western North Carolina when both adequate soil moisture and high ozone concentrations were present.
The presence of ozone symptoms is not an accurate indicator of how much growth loss has occurred to a sensitive plant from ozone exposure. Therefore, some air resource specialists rely upon measurements taken with ozone monitoring equipment in order to predict if growth loss has occurred. Ozone monitors provides over ozone readings from April through October.
Researchers and technical specialists have examined ways to summarize and use this extensive information. The Ozone Calculator is one tool that has been developed to estimate if ozone exposures recorded at a monitoring site could cause a growth loss to the vegetation.
There are two important statistics used to estimate the growth loss to vegetation when summarizing data from an ozone monitor. The N statistic is the number of hours when the measured ozone concentration is greater than or equal to 0. Experimental trials with a frequent number of peaks hourly averages greater than or equal to 0. For this reason, the W Lefohn and Runeckles, was developed as a biologically meaningful way to summarize hourly average ozone data.
The W places a greater weight on the measured values as the concentrations increase. Thus, it is possible for a high W value to occur with few to no hours above 0. Therefore, it is also necessary to determine the number of hours the ozone concentrations are greater than or equal to 0. It should also be noted the lack of N values does not mean ozone symptoms will not be present when field surveys are conducted.
The W exposure index does not utilize a threshold value, but weights differentially all hourly average concentrations. Significant weighting greater than 0 occurs at all hourly average concentrations above 0. The use of a 0 weighting for hourly average concentrations less than 0. The W has weighting of approximately 1 for all hourly average concentrations equal to and above 0. The weighting of 1 at these concentrations was based on informal discussions with vegetation researchers in California whose vegetation experienced repeated occurrences of hourly values equal to and above 0.
This was a subjective decision and it is recognized that every species will have a different weighting function. Taken from A. Vegetation's sensitivity to ozone varies -- not only between species, but also within a species.
For example, there may be two black cherry trees growing next to one another, and one will have severe ozone symptoms while the adjacent black cherry has no visible symptoms. Ozone contributes to what we typically experience as "smog" or haze, which still occurs most frequently in the summertime, but can occur throughout the year in some southern and mountain regions.
Although some stratospheric ozone is transported into the troposphere, and some VOC and NOx occur naturally, the majority of ground-level ozone is the result of reactions of man-made VOC and NOx.
Significant sources of VOC are chemical plants, gasoline pumps, oil-based paints, autobody shops, and print shops. Nitrogen oxides result primarily from high temperature combustion. Significant sources are power plants, industrial furnaces and boilers, and motor vehicles. Many people mistakenly believe that tropospheric ozone concentrations are high only in major urban areas, but high ambient ozone concentrations can and do occur anywhere.
It is also formed in smaller cities like Raleigh, NC and Cincinnati, OH, and it is transported hundreds of miles downwind from where it is created to affect ambient air quality in other urban and rural areas.
Where ozone is formed, peak concentrations usually occur during afternoon hours, when sunlight is the most intense. However, areas downwind of major sources of VOC and NOx may experience ozone peaks in the afternoon and evening, after wind has carried ozone and its VOC and NOx precursors many miles from their sources.
Thus, high ozone concentrations can occur in remote areas and at various times of day, including during the early evening or night.
Figure 1: U. This map depicts ozone concentrations by U. All orange, red, and purple areas exceeded the 8-hour ambient air quality standard for ozone during Stratospheric ozone is good ozone.
It forms about miles above the Earth's surface and forms a protective layer, called the ozone layer, that shields us from too much of the sun's harmful ultraviolet radiation UV.
Ground-level ozone is bad ozone. Ozone harms human health and the environment when it forms close to the ground. The most significant things that cause ground-level ozone to form are:.
We see higher ground-level ozone amounts most often in summer, due to increased amounts of UV radiation during the longer days, but ozone can still form in spring, fall, and even winter given the right conditions.
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