Characterization of emissions from burning methyl-bromide-treated crop biomass

Figures & data

Figure 1. Photos of a) raw alfalfa, b) burn test, and c) residual ash.

Table 1. Target compounds and sampling instrumentation/methods (U.S. EPA 2017a)

Analyte	Instrument/Method	Frequency
CO2	LICOR-820^b, NDIR	Continuous 10 Hz
CO	e2V EC4-500-CO^c, Electrochemical cell	Continuous 10 Hz
PM2.5	SKC Impactor^a/47 mm, 2 micron pore size Teflon filter/40 CFR Part 50 Appendix L (40 CFR Part 50, Appendix L 1987)	Batch 10 L min^−1
PM by size^d	DustTrak DRX 8533^e	Continuous 1 Hz
HBr/HCl	SKC cassette 225–9032^a, NIOSH Method 7907 (NIOSH 7907 2014), Na2CO3 coated quartz filter, U.S. EPA Method SW-846 Method 6850 (U.S. EPA Method 6850 2007)	Batch 2 L min^−1
PBDD/PBDF and PCDD/PCDF	Quartz filter/PUF/Modified U.S. EPA Method TO-9A (1999b)	Batch nominal 650 L min^−1
Volatiles	6 L SUMMA canister/U.S. EPA Method TO-15(1999c)	Batch 0.5 L min^−1
CO2, CO, CH4	6 L SUMMA canister/U.S. EPA Method TO 25C (2017a)	Batch 0.5 L min^−1
Carbonyls	DNPH^f cartridge/U.S. EPA Method TO-11A (1999a)	Batch 1 L min^−1
PAHs	Quartz filter/PUF/XAD-2/PUF, Modified U.S. EPA Method TO-9A (1999b)	Batch 5 L min^−1

^aSKC Inc., USA. ^bLI-COR Biosciences, USA. ^cSGX Sensortech, United Kingdom. ^dPM₁, PM_2.5, PM₄, PM₁₀ Total PM up to 15 µm. ^eTSI Inc. USA. ^fDNPH – 2,4-Dinitrophenylhydrazine.

Table 2. Bromine and chlorine in the raw biomass and ash

Biomass	Format	Br, ppm (RPD%; RSD %)	Cl, ppm (RPD%; RSD%)
Untreated Alfalfa	Raw Biomass (n = 2)	20.5 (5%)	4,370 (107%)
	Ash (n = 3)	20 (0%)	8,383 (59%)
	Amount to Ash^a, % (n = 6)	17	33
	Balance to Emissions^a, %	83	67
Treated Alfalfa	Raw Biomass (n = 2)	3,665 (61%)	3,170 (31%)
	Ash (n = 3)	6,220 (32%)	4,717 (32%)
	Amount to Ash^a, % (n = 7)	50	43
	Balance to Emissions^a, %	50	57

^aPercent of original Br and Cl mass

Table 3. Emission factor results

		Untreated alfalfa				Treated alfalfa
Pollutant	Unit	n^a	Average	Stand. Dev.^b	RSD^c	n^a	Average	Stand. Dev.^b	RSD^c
CO2	g kg^−1 biomass	3	1,587	46	2.9%	3	1,569	21	1.3%
CO	g kg^−1 biomass	3	138	22	16%	3	149	11	7.5%
CH4	g kg^−1 biomass	3	11	3.9	37%	3	11	1.2	10%
CO2	g C kg^−1 biomass	3	433	13	2.9%	3	428	5.6	1.3%
CO	g C kg^−1 biomass	3	59	9.6	16%	3	64	4.8	7.5%
CH4	g C kg^−1 biomass	3	14	5.1	37%	3	14	1.5	10%
MCE^d	Ratio, unitless	3	0.865	0.025	2.9%	3	0.856	0.011	1.3%
PM2.5	g kg^−1 biomass	9	47	12	25%	9	32	6.5	20%
HBr	mg kg^−1 biomass	3	ND (<38)^g			3	ND (<38)^g
HCl	mg kg^−1 biomass	3	ND (<39)^g			3	ND (<38)^g
Σ VOCs^e	g kg^−1 biomass	3	17.2	5.8	34%	3	16.5	2.5	15%
Σ Carbonyls^f	g kg^−1 biomass	1	12.3			1	15.6
Σ PCDD/PCDF	ng TEQ kg^−1 biomass	3	0.30	0.18	62%	3	3.60	0.71	20%
Σ PCDD/PCDF	ng kg^−1 biomass	3	18	8.2	46%	3	216	92	43%
Σ PBDD/PBDF	ng TEQ kg^−1 biomass	3	0.14	0.19	136%	3	0.051	0.011	98%
Σ PAH16	mg kg^−1 biomass	3	76.6	11.0	14%	3	160.2	8.6	5.4%
Σ PAH16 – TEQ	mg B[a]Peq kg^−1 biomass	3	0.52	0.071	14%	3	1.32	0.22	16%

^an = number of samples collected. ^b Stand. Dev. = standard deviation. ^c RSD = relative standard deviation. ^d MCE = modified combustion efficiency (∆CO₂/(∆CO₂+∆CO+∆CH₄)). ^e Sum of 124 VOCs. ^f Sum of 14 carbonyls. ^g Method detection limit.

Table 4. Selected VOC emission factors

	Untreated alfalfa			Treated alfalfa
	EF	Stand. Dev.	RSD	EF	Stand. Dev.	RSD
VOC	mg kg^−1 biomass		%	mg kg^−1 biomass		%
Acetone^a	2384	659	28	2123	388	18
Chloromethane^b	2147	866	40	1106	376	34
Vinyl Acetate^b	2063	636	31	1234	349	28
Propene	2042	752	37	2253	166	7.4
Acetonitrile^b	1906	700	37	2392	473	20
Methyl Acetate	1422	599	42	1006	123	12
Toluene^a,b,c	1069	559	52	1077	99	9.2
2-Butanone^b	980	347	35	753	72	9.6
Acrolein^b	642	340	53	607	326	54
Benzene^a,b,c	507	122	24	820	37	4.5
1,3-Butadiene^a,b	443	141	32	627	22	3.5
Styrene^a,b,c	233	129	56	296	20	6.8
Acrylonitrile^b	211	93	44	382	26	6.8
Ethylbenzene^a,b,c	181	100	55	205	22	11
m,p-Xylenes^a,b,c	173	79	46	153	11	7.5
Ethanol^a	91	37	41	77	19	25
o-Xylene^a,b,c	68	37	54	64	7.1	11
n-Hexane^b	59	30	51	51	12	24
n-Heptane	43	22	52	34	4.2	12
Indene	37	23	62	63	2.2	3.5
1,2,4-Trimethylbenzene^a,c	35	24	70	33	4.1	12
n-Propylbenzene^c	33	21	63	32	5.4	17
2-Hexanone	28	11	40	22	2.5	11
n-Nonane	25	15	60	18	3.0	16
d-Limonene	24	6.2	25	20	7.8	39
Tetrahydrofuran (THF)	18	5.0	28	11	1.7	15
Indan	12	7.2	60	12	1.1	10
Thiophene	11	4.6	40	14	1.3	9.1
Chloroethane^b	11	4.6	42	7.8	1.4	18
1,3,5-Trimethylbenzene^a,c	10	6.4	65	8.6	1.3	15
Cumene^b	6.0	3.4	57	7.6	0.6	7.9
Methyl bromide^b	2.3	1.0	43	739	207	28
Bromodichloromethane	ND (1.1)^d			ND (1.5)^d
Dibromochloromethane	ND (1.2)^d			ND (1.6)^d
1,2-Dibromoethane	ND (1.2)^d			ND (1.6)^d
Bromoform^b	ND (1.1)^d			ND (1.5)^d
1,2-Dibromo-3-chloropropane^a	ND (0.73)^d			ND (0.93)^d
Vinyl Bromide	ND (1.6)^d			ND (2.1)^d
Dimethyl bromide	ND (1.5)^d			ND (1.9)^d
Bromobenzene	ND (1.8)^d			ND (2.5)^d

^aOn US EPA’s target list of photochemical assessment monitoring stations (PAMS) compounds (U.S. EPA 2013).

^bOn US EPA’s list of hazardous pollutants (HAP) (U.S. EPA Hazardous Air Pollution List 2008).

^csecondary organic aerosol potential (SOAP) compound (2013).

^dMethod detection limit within parentheses. The VOCs presented here are based on number of samples collected and their list of relevance to EPA’s HAP and PAMS lists and if Br-VOC. Full list of the 124 VOCs analyzed from SUMMA Canisters can be found in supplemental information Table SI-1.

Figure 2. Modified combustion efficiency (MCE) versus VOC emission factors.

Table 5. Carbonyl emission factors

Carbonyl	Untreated alfalfa			Treated alfalfa
	n^a	mg kg^−1 biomass	MDL^b	n^a	mg kg^−1 biomass	MDL^b
Formaldehyde^c,d	1	1,969	0.21	1	2,027	0.25
Acetaldehyde^c,d	1	4,683	0.82	1	6,623	0.96
Acetone^d	1	2,089	1.15	1	2,876	1.34
Propionaldehyde	1	1,133	0.86	1	1,300	1.00
Crotonaldehyde	1	305	1.15	1	390	1.34
Butyraldehyde	1	1,229	0.97	1	1,313	1.13
Benzaldehyde	1	543	1.64	1	551	1.91
Isovaleraldehyde	1	392	1.92	1	485	2.23
Valeraldehyde	1	ND	1.32	1	ND	1.53
o-Tolualdehyde	1	ND	2.66	1	ND	3.09
m-Tolualdehyde	1	ND	2.47	1	ND	2.87
p-Tolualdehyde	1	ND	2.25	1	ND	2.62
Hexaldehyde	1	ND	1.53	1	ND	1.78
2,5-Dimethylbenzaldehyde	1	ND	1.95	1	ND	2.27

^an = number of samples collected.

^bMDL = method detection limit in mg/kg biomass.

^cOn EPA’s list of hazardous pollutants (HAPs) (2008).

^dOn US EPA’s target list of photochemical assessment monitoring stations (PAMS) compound (2013).

Figure 3. PCDD/PCDF and PBDD/PBDF from treated and untreated alfalfa biomass. Error bars represent RSD.

Table 6. PAH emission factors from open burning of treated and untreated alfalfa

	Untreated alfalfa			Treated alfalfa
PAHs	mg kg^−1 biomass	Stand. Dev.	RSD %	mg kg^−1 biomass	Stand. Dev.	RSD %
Naphthalene	52.40	10.04	19	107.06	0.46	0.43
Acenaphthylene	5.42	0.62	11	18.08	3.42	19
Acenaphthene	1.70	0.30	18	2.14	0.31	15
Fluorene	4.69	1.55	33	5.48	1.44	26
Phenanthrene	5.39	0.76	14	11.23	2.06	18
Anthracene	1.65	0.19	11	2.76	0.45	16
Fluoranthene	1.58	0.25	16	3.85	0.74	19
Pyrene	1.42	0.22	16	3.55	0.64	18
Benzo(a)anthracene	0.43	0.15	36	1.07	0.24	22
Chrysene	0.75	0.15	20	1.68	0.31	18
Benzo(b)fluoranthene	0.28	0.040	15	0.63	0.11	18
Benzo(k)fluoranthene	0.25	0.045	18	0.75	0.15	20
Benzo(a)pyrene	0.31	0.045	14	0.80	0.14	18
Indeno(1,2,3-cd)pyrene	0.17	0.055	33	0.48	0.13	27
Dibenz(a,h)anthracene	0.034	0.011	32	0.10	0.029	30
Benzo(ghi)perylene	0.16	0.036	23	0.49	0.11	23
SUM PAH16	76.6	11.0	14	160.2	8.57	5.4

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Data availability statement

Data used in the writing of this manuscript is available at the U.S. Environmental Protection Agency’s Environmental Dataset Gateway (https://edg.epa.gov).