Spatial distribution of tropospheric ozone in national parks of California: interpretation of passive-sampler data.

John D. Ray

doi:10.1100/tsw.2001.83

Abstract

The National Park Service (NPS) has tested and used passive ozone samplers for several years to get baseline values for parks and to determine the spatial variability within parks. Experience has shown that the Ogawa passive samplers can provide ±10% accuracy when used with a quality assurance program consisting of blanks, duplicates, collocated instrumentation, and a standard operating procedure that carefully guides site operators. Although the passive device does not meet EPA criteria as a certified method (mainly, that hourly values be measured), it does provide seasonal summed values of ozone. The seasonal ozone concentrations from the passive devices can be compared to other monitoring to determine baseline values, trends, and spatial variations. This point is illustrated with some kriged interpolation maps of ozone statistics. Passive ozone samplers were used to get elevational gradients and spatial distributions of ozone within a park. This was done in varying degrees at Mount Rainier, Olympic, Sequoia–Kings Canyon, Yosemite, Joshua Tree, Rocky Mountain, and Great Smoky Mountains national parks. The ozone has been found to vary by factors of 2 and 3 within a park when average ozone is compared between locations. Specific examples of the spatial distributions of ozone in three parks within California are given using interpolation maps. Positive aspects and limitations of the passive sampling approach are presented.

Highlights

An extensive network of ozone monitoring stations exists in the U.S.; most of these monitors are located in urbanized areas
TheScientificWorld (2001) 1, 483-497 has become evident that rural national parks, including several in California, have ozone concentrations[1] that exceed the National Ambient Air Quality Standard (NAAQS) that was designed to protect human health and welfare
Because ozone monitors operated according to EPA guidelines are typically within ±5% but can be as high as ±15%, the passive samplers would be expected be vary by at least a similar amount

Summary

Introduction

An extensive network of ozone monitoring stations exists in the U.S.; most of these monitors are located in urbanized areas. Because most of the precursor emissions and the highest ozone values are generally found in urban areas, a higher density of monitoring stations has been used to characterize the spatial patterns of ozone among the population centers. TheScientificWorld (2001) 1, 483-497 has become evident that rural national parks, including several in California, have ozone concentrations[1] that exceed the National Ambient Air Quality Standard (NAAQS) that was designed to protect human health and welfare (which includes natural resources). Because only limited emissions are local to these monitors, the assumption has been that the measurements are representative of ozone concentrations over areas anywhere from 1 to 60 km or more from the station. Three national parks within California provide rural areas with significant natural resources where complex terrain and vegetation patterns make it unlikely that the ozone distribution is uniform

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Conclusion