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Growth Factor as Related to HC and NOx from Automotive Sources

Although local traffic density has been taken as the principal index in the discussion of carbon monoxide control, an increase in central city area at an urban location, and an increase in total vehicular traffic may also be considered to bear a relationship to total pollutant emitted.

One

This could be related to pollutant concentration, particularly in cities which continue to show central growth. method of approximating this mass effect has been to weight traffic density as 90% of the total. To this is added 10% of an urban mass vehicular traffic factor. The latter includes an expanded urban area, and an expanded total vehicular traffic (Attachment A-3, Table 1 shows both types of information).

For example, Los Angeles shows a significant broadening of the high traffic density area. It is this city which has the highest ambient air concentrations of HC and NOx. It would appear appropriate to calculate a mass-related and density-related growth factor for HC and NOx, as follows:

Traffic Density

Increase to 1980:

22.5% Ave.

23 yrs. 40% 13 yrs.

Increase to 1990, extrapolated 22.5% ×
from above:

Central Business District Vehicular Traffic

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Traffic Density x 90% + Central Vehicular Traffic x 10% = Total

40% x .90 + 173% x .10 =

53% Increase

This corresponds to a growth factor of 1.53.

Alternatively, the simple increase in traffic density in

Los Angeles would indicate a growth factor of 1.40.

Using these modified growth factors, emission standards

can be calculated by the roll-back technique:

on the growth factor used. Since high concentrations of HC, CO and NOx are problems only in major cities, the appropriate growth factors of 1.40 to 1.46 are considered more representa

tive. Even these growth factors probably overstate

the increase

in motor vehicle useage in areas such as New York City and

Chicago.

As a consequence, the required emission control at the low end of the range shown is probably still somewhat stricter

than required of motor vehicles.

In summary, the required automotive emission control to

achieve primary air quality standards is:

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The high end of the range shown is considered to be a

better estimate of the control required in the urban areas,

which is the focus of the air pollution problem.

Range in Growth Factor

Following is a summary of growth factors:

1.66 Nationwide growth factor

See Attachments

1.53

1.40

1.10

1.0

A-1, A-2, A-3: This is too high

for urban areas, where pollution is a problem.

It is used here as the high end of the possible
range.

An urban area-traffic density growth factor.
Considered to be representative of Los Angeles.

A simple traffic density growth factor, calculated
for Los Angeles.

An urban area-traffic density factor calculated
for the central city areas of Chicago or New York
City, where traffic density is already at a maximum.

A simple factor, indicating that no growth in
traffic density is taking place in central Chicago
and New York City.

VEHICLE POPULATION GROWTH PROJECTIONS

Ref. (19) of Barth paper.

TABLE 5-1. Purchases of Automobiles, 1950,
1955, 1960, and Projections to 2000

(Million vehicles)

addi

domestic

5.0

2.0

7.0

Million persons

Medium

3/ Recorded figures are shown for 1967 through 1970.

ATTACHMENT A-2