CHART TO MEASURE OPACITY OF GREY OR BLACK EMISSIONS
Opacity is evaluated using a chart in good condition, printed within the last 5 years, that complies with the following specifications:
The Micro Ringelmann Chart is printed on a card 12.8 cm long by 8.6 cm wide on which opacities of 20%, 40%, 60% and 80% (No. 1, No. 2, No. 3 and No. 4 respectively) are represented in order, in an alignment of vertical rectangles 24 mm by 58 mm (±1 mm), within which a 13 mm (±1 mm) slit is made (see figure below). Each degree of opacity is represented by an ultra fine grid of black lines on a white background, according to the following specifications:
For opacity No. 1: Black grid lines measuring 0.055 mm that are 0.555 mm apart with white spaces 0.5 mm by 0.5 mm.
For opacity No. 2: Black grid lines measuring 0.128 mm that are 0.555 mm apart with white spaces 0.427 mm by 0.427 mm.
For opacity No. 3: Black grid lines measuring 0.205 mm that are 0.555 mm apart with white spaces 0.35 mm by 0.35 mm.
For opacity No. 4: Black grid lines measuring 0.305 mm that are 0.555 mm apart with white spaces 0.25 mm by 0.25 mm.
The month and year the chart was printed must be indicated in the lower left-hand corner.
No.1 No.2 No. 3 No. 4
MICRO RINGELMANN CHART
Slit in the card
Opacity is measured from an observation point between 30 and 400 m from the emission point. The observation point must allow full view of the emissions. The sun must be oriented in the 140º sector to the observer’s back. The observer must make observations using a line of vision that is perpendicular to the direction of the plume.
The observer holds the chart at arm’s length and looks at the emission through the slit in the card. The observer notes the scale number (No. 1, 2, 3 or 4) that best suits the opacity observed. No. 0 is used to indicate that no emission is visible and No. 4 applies to an opacity of 100%.
Opacity evaluation must be carried out where the opacity is maximum, in a part of the plume where there is no condensed water vapour. The observer must not look continually at the plume but rather must observe the plume momentarily every 15 seconds. Opacity evaluation is carried out over a 60-minute period without interruption between each period (240 observations in 60 minutes) or two 30-minute periods with an interruption at half time (120 observations in 30 minutes, twice).
Where water vapour condenses and becomes visible at a certain distance from the emission point, the opacity must be evaluated between the emission point and the condensation point of the water vapour.
When condensed water vapour is present in the plume, at its emission point, the opacity of the plume must be observed at the point where the vapour is no longer visible.
The following formula is used to establish emission opacity:
| P = NEU at opacity No. 1 X 20% |
| ____________________________ |
| number of observations |
| where P is the percentage of emission opacity and NEU is |
| the number of equivalent units. |
| Each number on the chart represents as many equivalent |
| units. |
A single observation may suffice for the application of section 129.