METHOD 9 - VISUAL DETERMINATION OF THE OPACITY OF EMISSIONS FROM STATIONARY SOURCES STACK EMISSION

1.  Principle and Applicability 

1.1 Principle. 

The opacity of emissions from stationary sources is determined visually by a qualified 

observer. 

1.2 Applicability. 

This method is applicable for the determination of the opacity of emissions from 

stationary sources pursuant to §60.11(b) and for qualifying observers for visually determining opacity of emissions. 

2.  Procedures 

The observer qualified in accordance with section 3 of this method shall use the following procedures for visually determining the opacity of emissions: 

2.1 Position. 

The qualified observer shall stand at a distance sufficient to provide a clear view of the 

emissions with the sun oriented in the 140° sector to his back. Consistent with maintaining the above 

requirement, the observer shall, as much as possible, make his observations from a position such that his 

line of vision is approximately perpendicular to the plume direction, and when observing opacity of 

emissions from rectangular outlets (e.g., roof monitors, open baghouses, noncircular stacks), 

approximately perpendicular to the longer axis of the outlet. The observer's line of sight should not 

include more than one plume at a time when multiple stacks are involved, and in any case the observer 

should make his observations with his line of sight perpendicular to the longer axis of such a set of 

multiple stacks (e.g., stub stacks on baghouses). 

2.2 Field Records. 

The observer shall record the name of the plant, emission location, type facility, 

observer's name and affiliation, a sketch of the observer's position relative to the source, and the date on a field data sheet (Figure 9–1). The time, estimated distance to the emission location, approximate wind 

direction, estimated wind speed, description of the sky condition (presence and color of clouds), and 

plume background are recorded on a field data sheet at the time opacity readings are initiated and 

completed. 

2.3 Observations. 

Opacity observations shall be made at the point of greatest opacity in that portion of the plume where condensed water vapor is not present. The observer shall not look continuously at the plume, but instead shall observe the plume momentarily at 15-second intervals. 

2.3.1 Attached Steam Plumes. 

When condensed water vapor is present within the plume as it emerges 

from the emission outlet, opacity observations shall be made beyond the point in the plume at which 

condensed water vapor is no longer visible. The observer shall record the approximate distance from the emission outlet to the point in the plume at which the observations are made. 

2.3.2 Detached Steam Plume. 

When water vapor in the plume condenses and becomes visible at a distinct 

distance from the emission outlet, the opacity of emissions should be evaluated at the emission outlet 

prior to the condensation of water vapor and the formation of the steam plume. 

2.4 Recording Observations.

Opacity observations shall be recorded to the nearest 5 percent at 15-second  intervals on an observational record sheet. (See Figure 9–2 for an example.) A minimum of 24 observations shall be recorded. Each momentary observation recorded shall be deemed to represent the average opacity of emissions for a 15-second period.

2.5 Data Reduction.

Opacity shall be determined as an average of 24 consecutive observations recorded at 

15-second intervals. Divide the observations recorded on the record sheet into sets of 24 consecutive 

observations. A set is composed of any 24 consecutive observations. Sets need not be consecutive in time and in no case shall two sets overlap. For each set of 24 observations, calculate the average by summing the opacity of the 24 observations and dividing this sum by 24. If an applicable standard specifies an averaging time requiring more than 24 observations, calculate the average for all observations made during the specified time period. Record the average opacity on a record sheet. (See Figure 9–1 for an example.)