Smog Charts Record 3 Pollutant Readings

With this edition, The Times begins publishing a daily air quality chart showing levels of three pollutants recorded at monitoring stations across the Los Angeles Basin.

Since last summer, most editions have carried a chart showing hourly ozone averages for the previous day at selected locations in the four-county South Coast air basin. The chart now will display readings for two added contaminants--nitrogen dioxide and carbon monoxide--for all areas where those pollutants are measured.

Reporting three air pollutants will present a more complete picture of air quality. Some winter days that appeared “clean” when ozone was reported alone now may show higher levels of other contaminants. The accompanying illustration shows conditions for Dec. 1, 1984, measuring ozone alone and measuring three pollutants.

Olympic Development

The Times is the only newspaper to publish such charts, which were developed as part of the coverage of the 1984 Olympics.

The charts are drawn by computer from data made available by the South Coast Air Quality Management District. Because the pollutants are measured differently, the district converts readings to a common scale; all pollutants are seen in relation to a “clean air standard.”

To aid readers in understanding the readings, shading has been added. If all readings are within the white, the air was considered officially clean. On days with little pollution, readings may be superimposed or difficult to distinguish; so long as all readings are in the white, the air quality district believes there was no ill health effect.

Readings in the light gray area show air that was unhealthy for sensitive people. Readings in the darker shaded area show air that was unhealthy for everyone. Any measurement above the line labeled for second-stage episodes shows air that was hazardous for everyone. During periods of such elevated readings, the air quality management district issues warnings to reduce driving and some industrial processes.

It will be unusual to see all three pollutants elevated on the same day or at the same hour because the conditions that cause them differ and are mutually exclusive, according to Jim Birakos, deputy executive officer of the district.

Here is a closer look at each pollutant:

Ozone, which is pungent but invisible, results when strong sunlight causes a reaction between hydrocarbons and nitrogen oxides. It is a daytime pollutant, reaching its highest levels in the afternoon and inland, where prevailing breezes concentrate the ingredients, Birakos said. The more sunlight, the more ozone, all other factors being equal. Therefore it is most severe in July, August and September. Ozone is reduced by reducing hydrocarbons and nitrogen oxides in the air.

The chart reflects the federal clean air standard of .12 parts per million of ozone as an hourly average, and the state first- and second-stage episode levels of .20 ppm and .35 ppm, respectively.

Violations of these ozone standards generally have been decreasing, but the basin is far from meeting the legally required federal standard and does not expect to comply until sometime after the year 2000.

The number of episodes is strongly influenced by the weather. In 1979 the district set a record of 120 first-stage episodes, Birakos said. Last year, it set another record by not recording any second-stage episodes. But this year, a second-stage episode already has been measured--in Norco on April 13, which is before the usual smog season.

Nitrogen dioxide, a yellowish-brownish gas, is a byproduct of combustion acting on the natural nitrogen in the air. Nitrogen dioxide impairs breathing, especially among children. It also harms vegetation, and, when combined with water vapor, produces nitric acid rain or fog.

Motor vehicles produce about 60% and the rest comes from industrial combustion sources, including power plants and refinery heaters. Nitrogen dioxide is worst during evening hours in November and December and near the coast, where temperature inversions prevent it from being dispersed, Birakos said.

The clean air standard for nitrogen dioxide used in the Times chart is .25 parts per million averaged over one hour, set by the federal government. The first-stage level is reached at .60 ppm and the second-stage level is 1.2 ppm. The district experienced four days when the first-stage level was exceeded in 1983, two in 1984 and none so far this year, according to Birakos.

Carbon monoxide, which is colorless, odorless and tasteless, is harmful because it displaces oxygen in the bloodstream. It is a product of incomplete combustion and nearly all of it comes from motor vehicles. It is most concentrated at about sunrise and during winter months, especially November and December, when strong surface inversions and calm winds trap it near the surface. It quickly disperses after sunrise as the cool air near the surface warms and the inversion diminishes, Birakos said.

The standard used for the Times charts is based on an eight-hour moving average and is set by the federal government at 9 parts per million, with the first-stage episode level occurring at 15 ppm and the second-stage level at 30 ppm. The district had nine first-stage carbon monoxide episodes in 1983 and again in 1984. Two have occurred so far this year.