Quantification of emission factor uncertainty

Figures & data

Table 1. Definition of ratings used for test data quality rating

Test Data Quality Rating Letter	Description
A	Tests are performed by a sound methodology and are reported in enough detail for adequate validation.
B	Tests are performed by a generally sound methodology, but lacking enough detail for adequate validation.
C	Tests are based on an unproven or new methodology, or are lacking a significant amount of background information
D	Tests are based on a generally unacceptable method, but the method may provide an order-of-magnitude value for the source.

Table 2. Definition of AP-42 emission factor ratings

Letter Rating	Description
A—Excellent	Factor is developed from A- and B-rated source test data taken from many randomly chosen facilities in the industry population. The source category population is sufficiently specific to minimize variability.
B—Above average	Factor is developed from A- or B-rated test data from a “reasonable number” of facilities. Although no specific bias is evident, it is not clear if the facilities tested represent a random sample of the industry. As with an A rating, the source category population is sufficiently specific to minimize variability.
C—Average	Factor is developed from A-, B-, and/or C-rated test data from a reasonablenumber of facilities. Although no specific bias is evident, it is not clear if the facilities tested represent a random sample of the industry. As with the A rating, the source category population is sufficiently specific to minimize variability.
D—Below average	Factor is developed from A-, B-, and/or C-rated test data from a smallnumber of facilities, and there may be reason to suspect that these facilities do not represent a random sample of the industry. There also may be evidence of variability within the source population.
E—Poor	Factor is developed from C- and D-rated test data, and there may be reason tosuspect that the facilities tested do not represent a random sample of the industry. There also may be evidence of variability within the source category population.

Table 3. Summary statistics of the 21 different SCCs

SCC	Fuel Type	Mechanism	AP-42 Grade	AP-42 EF(Lb/Ton)	CEMS Mean(Lb/Ton)	% Diff.
10100201	Bituminous/subbituminous coal	Pulverized coal: wet bottom (bituminous coal)	D	31	15.43	101.0%
10100202	Bituminous/subbituminous coal	Pulverized coal: dry bottom (bituminous coal)	A	12	11.46	4.7%
10100203	Bituminous/subbituminous coal	Cyclone furnace (bituminous coal)	A	33	22.28	48.1%
10100204	Bituminous/subbituminous coal	Spreader stoker	C	11	8.68	26.8%
10100212	Bituminous/subbituminous coal	Pulverized coal: dry bottom, tangential (bituminous coal)	A	10	10.27	−2.7%
10100221	Bituminous/subbituminous coal	Pulverized coal: wet bottom (subbituminous coal)	E	24	7.49	220.6%
10100222	Bituminous/subbituminous coal	Pulverized coal: dry bottom (bituminous coal)	A	7.4	7.30	1.4%
10100223	Bituminous/subbituminous coal	Cyclone furnace (subbituminous coal)	C	17	13.13	29.5%
10100226	Bituminous/subbituminous coal	Pulverized coal: dry bottom, tangential (subbituminous coal)	A	7.2	5.66	27.2%
10100301	Lignite	Pulverized coal: dry bottom, wall fired	C	6.3	4.57	37.8%
10100302	Lignite	Pulverized coal: dry bottom, tangential fired	A	7.1	4.46	59.0%
10100303	Lignite	Cyclone furnace	C	15	9.46	58.6%
10100401	Residual oil	Grade 6 oil: normal firing	A	1.97	1.51	30.1%
10100404	Residual oil	Grade 6 oil: tangential firing	A	1.34	1.79	−24.9%
10100501	Distillate oil	Grade 1 and 2 oils	D	1.01	2.02	−50.0%
10100601	Natural gas	Electric generation, boilers >100 million BTU/hr except tangential	A	0.19	0.20	−6.9%
10100602	Natural gas	Boilers <100 million BTU/hr except tangential	B	0.1	0.30	−66.2%
10100604	Natural gas	Tangentially fired units	A	0.17	0.14	18.9%
10200601	Natural gas	Industrial, boilers >100 million BTU/hr	A	0.19	0.17	10.9%
20100201	Natural gas	Electric generation, turbine	A	0.32	0.08	286.8%
20200201	Natural gas	Industrial, turbine	A	0.32	0.32	0.5%
Notes: EF = emission factor; AP-42 Grade = the letter grade found in the AP-42; AP-42 EF = emission factor as found in WebFIRE; %Diff. = AP-42 emission factor minus the mean emission factor divided by the AP-42 emission factor.

Figure 1. SCC 10100203 (bituminous coal, cyclone furnace) boxplots by plants before 2% trim. The NO_x emission factor is in units of lbs/ton.

Figure 2. SCC 10100203 (bituminous coal, cyclone furnace) boxplots by plants after 2% trim. The NO_x emission factor is in units of lbs/ton.

Figure 3. Time plot of NO_x emission factors for SCC 10100203, plant 963 (bituminous coal, cyclone furnace), with control period included; in lbs/ton.

Figure 4. Time plot of NO_x emission factors for SCC 10100203, plant 963 (bituminous coal, cyclone furnace), with control period not included; in lbs/ton.

Figure 5. Time plot of NO_x emission factors for SCC 10100203, plant 2364 (bituminous coal, cyclone furnace), with control period included; in lbs/ton. Data were removed from this plant beginning on April 1, 1998.

Figure 6. Distribution of NO_x emission factors for SCC 10100203 (bituminous coal, cyclone furnace), with the mean emission factor and AP-42 emission factor labeled. Units are in lbs/ton.

Table 4. Letter grades and assumed associated sample sizes

Letter Grade	Sample Size (n)
A	25
B	10
C	5
D	3
E	1

Table 5. SCCs and their corresponding uncertainties for A through E letter grades

SCC	Fuel Type	Mechanism	A(n = 25)	B(n = 10)	C(n = 5)	D(n = 3)	E(n = 1)
10100201	Bituminous/subbituminous coal	Pulverized coal: wet bottom (bituminous coal)	30%	51%	64%	72%	84%
10100202	Bituminous/subbituminous coal	Pulverized coal: dry bottom (bituminous coal)	21%	43%	57%	66%	80%
10100203	Bituminous/subbituminous coal	Cyclone furnace (bituminous coal)	16%	37%	53%	63%	78%
10100204	Bituminous/subbituminous coal	Spreader stoker	25%	47%	61%	69%	82%
10100212	Bituminous/subbituminous coal	Pulverized coal: dry bottom, tangential (bituminous coal)	13%	34%	50%	60%	76%
10100221	Bituminous/subbituminous coal	Pulverized coal: wet bottom (subbituminous coal)	3%	18%	34%	46%	67%
10100222	Bituminous/subbituminous coal	Pulverized coal: dry bottom (bituminous coal)	25%	46%	60%	69%	82%
10100223	Bituminous/subbituminous coal	Cyclone furnace (subbituminous coal)	12%	33%	49%	59%	76%
10100226	Bituminous/subbituminous coal	Pulverized coal: dry bottom, tangential (subbituminous coal)	23%	44%	59%	68%	81%
10100301	Lignite	Pulverized Coal: Dry Bottom, Wall Fired	24%	45%	59%	68%	81%
10100302	Lignite	Pulverized Coal: Dry Bottom, Tangential Fired	5%	22%	39%	50%	70%
10100303	Lignite	Cyclone Furnace	8%	27%	43%	54%	73%
10100401	Residual oil	Grade 6 oil: normal firing	19%	40%	55%	65%	79%
10100404	Residual oil	Grade 6 oil: tangential firing	17%	38%	54%	63%	78%
10100501	Distillate oil	Grade 1 and 2 oils	30%	51%	64%	72%	84%
10100601	Natural gas	Electric generation, boilers >100 million BTU/hr except tangential	42%	61%	72%	78%	87%
10100602	Natural gas	Boilers <100 million BTU/hr except tangential	28%	49%	63%	71%	83%
10100604	Natural gas	Tangentially fired units	26%	47%	61%	69%	82%
10200601	Natural gas	Industrial, boilers >100 million BTU/hr	39%	59%	70%	77%	86%
20100201	Natural gas	Electric generation, turbine	69%	80%	86%	89%	94%
20200201	Natural gas	Industrial, turbine	37%	57%	69%	76%	86%

Table 6. Emission factor data quality rating uncertainties for the different pollutant and source category combinations

Source Category/Pollutant	A(n = 25)	B(n = 10)	C(n = 5)	D(n = 3)	E(n = 1)
Hot mix batch filterable PM	64%	77%	83%	87%	93%
Hot mix batch inorganic cond	63%	76%	83%	87%	92%
Hot mix batch organic cond	62%	75%	82%	86%	92%
Hot mix benzene	49%	66%	76%	81%	89%
Hot mix drum filterable PM	47%	65%	75%	80%	88%
Hot mix drum inorganic cond	56%	71%	79%	84%	91%
Hot mix drum organic cond PM	66%	78%	85%	88%	93%
Hot mix formaldehyde	59%	73%	81%	85%	91%
OSB-HP PM filterable	55%	70%	79%	83%	90%
Refuse arsenic	48%	66%	75%	81%	89%
Refuse cadmium	58%	72%	80%	85%	91%
Refuse CO	45%	63%	74%	79%	88%
Refuse HCl FF	62%	75%	82%	86%	92%
Refuse HCl uncontrolled	25%	47%	61%	69%	82%
Refuse lead	51%	68%	77%	82%	90%
Refuse mercury	58%	73%	81%	85%	91%
Refuse nickel	44%	63%	73%	79%	88%
Refuse NOx uncontrolled	1%	11%	26%	38%	61%
Refuse PM DS FF	38%	58%	69%	76%	86%
Refuse PM ESP	58%	72%	80%	85%	91%
Refuse PM ESP RDF	68%	79%	85%	89%	93%
Refuse PM RDF uncontrolled	18%	40%	55%	64%	79%
Refuse PM SD ESP	30%	51%	64%	72%	83%
Refuse PM SD FF	55%	71%	79%	84%	91%
Refuse PM uncontrolled	28%	49%	63%	71%	83%
Refuse SO2	32%	53%	66%	73%	84%
Wood comb acetaldehyde	67%	79%	85%	88%	93%
Wood comb arsenic	78%	86%	90%	92%	96%
Wood comb benzene	71%	82%	87%	90%	94%
Wood comb cadmium	67%	79%	85%	88%	93%
Wood comb chromium	70%	81%	86%	89%	94%
Wood comb CO	51%	68%	77%	82%	90%
Wood comb formaldehyde	71%	81%	87%	90%	94%
Wood comb lead	74%	84%	88%	91%	95%
Wood comb mercury	69%	80%	86%	89%	94%
Wood comb nickel	74%	83%	88%	91%	95%
Wood comb NOx	15%	36%	52%	62%	77%
Wood comb PM cond	53%	69%	78%	83%	90%
Wood comb PM filter drywood	27%	49%	62%	70%	83%
Wood comb PM filter MC drywood	24%	45%	60%	68%	81%
Wood comb PM filter MC wetwood	59%	74%	81%	85%	92%
Wood comb PM filter wetwood	36%	57%	68%	75%	86%
Wood comb PM filter WS wetwood	11%	32%	48%	58%	75%
Wood comb SO2	67%	79%	85%	88%	93%

Table 7. Uncertainty ranges (the interquartile range) for emission factor data quality indicators

A Uncertainty(n = 25)	B Uncertainty(n = 10)	C Uncertainty(n = 5)	D Uncertainty(n = 3)	E Uncertainty(n = 1)
25–62%	46–75%	60–82%	69–86%	82–92%

Figure 7. Hot mix batch filterable PM—example of a log-normal distribution. The emission factor units are lbs/ton.