CHART TO MEASURE OPACITY OF GREY OR BLACK EMISSIONS
Opacity of grey or black emissions into the atmosphere is measured using a Micro Ringelmann Chart in good condition, printed within the last 5 years, that meets 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. 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.
Opacity is measured from an observation point located between 30 m and 400 m from the emission point. The observation point must be such that the observer’s line of vision is perpendicular to the direction of the plume and that the sun is oriented in the 140 º sector to the observer’s back.
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 opacity of 100%. Momentary and punctual observations are noted every 15 seconds. Opacity evaluation is carried out over a 60-minute period without interruption (240 observations over 60 minutes) or over 2 30-minute periods with an interruption after the first 30-minute period (120 observations over 30 minutes, twice). Each observation is considered to be representative of the opacity for a 15-second period.
Opacity evaluation must be carried out at the point of maximum opacity, in a part of the plume where there is no condensed water vapour. 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.