VOCs in Alberta’s Industrial Heartland

AMS Annual Conference

Rachel Mintz*, Robert D. McWhinney, Beau Chaitan, Curtis Englot, Réal D’Amours

Environment Canada

January 2009

Contents

• The Study Region

• VOC Monitoring

• Analysis: – Simple Statistics– Comparison to other Canadian cities– Principal Component Analysis– Lagrangian-stochastic modeling

• Summary

The Study Region: Fort Saskatchewan

The Study Region: Fort Saskatchewan

Mixture of anthropogenic and biogenic emissions:

City of Edmonton, pop. ~1 million

City of Fort Saskatchewan, pop. ~15,000.

National Park, 190 km2

Industrial Zone, over 30 facilities, downstream oil & gas petrochemical

New upgraders facilities proposed for the region; however current economic conditions have delayed several projects.

The Study Region: Fort Saskatchewan

• One facility manufacturing 1,2-dichloroethane in Canada located in the Fort Saskatchewan region.

• 1,2-dichloroethane has a long atmospheric lifetime: estimated range of 43 to 111.

• Other specific VOCs emitted in the region that aid in characterizing industry related emissions include vinyl chloride, styrene and HCFC-22.

Data collected in this VOC study prior to the construction of proposed oil sands upgraders is important as it provides baseline data.

VOC Monitoring

• September 2004 – March 2006• Six sites • Sampled for 24-hours, every 6 days

(according to the National Air Pollutant Surveillance Network)

• Xontechs and Summa canisters• Chemical analysis with GC/MS• 150 VOCs:

– Common suite of C3 –C12 ground-level ozone precursors, toxic chlorinated hydrocarbons and compounds found on the Canadian Environmental Protection Act’s Priority Substance List (CEPA, 1999).

Monthly Averages – All VOCs

0

20

40

60

80

100

120

140

160

180

200

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Month

Ave

rage

Tot

al M

eas

ured

VO

C C

onc

entr

atio

n (

µg/

m3)

Site A

Site B

Site C

Site D

Site E

Site F

Fort Sask Average

Planned flaring event

at a NGL facility

0

1

2

3

4

5

6

7

8

9

10

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Month

Ave

rag

e T

ota

l Me

asu

red

Mo

no

terp

en

e a

nd

Iso

pre

ne

C

on

cen

tra

tion

s (u

g/m

3)

Site A

Site B

Site C

Site D

Site E

Site F

Fort SaskAverage

Monthly Averages – Biogenic species

Trick or treat?Sample taken on October 31, 2005

Comparison to other Canadian Sites

• Comparison of averages was made to other Canadian cities (selected NAPS stations).

• Fort Saskatchewan shows higher concentrations than the “Group Average” for eight VOCs: 1,2-dichloroethane, 1-hexene/2-methyl-1-pentene, 2-methylhexane, 3-methylhexane, 4-methylheptane, heptane, p-cymene and vinyl chloride.

• 142 of the VOCs had concentrations lower than the other Canadian cities.

• Of the 8 substance identified, 4 had unique events (planned flaring and Halloween sample) that skewed the distribution and increased the overall average.

Principal Component Analysis

What is PCA?• Multivariate statistical

analysis method.• Finds underlying groups

of correlated variables (called factors) within a large data set.

• With VOC data, factors often help to identify emission sources as VOCs originating from one source should be correlated.

VOC1 VOC2 … VOCn

Sample1

Sample2

…

Samplen

Covariance Matrix

Eigenvalues and eigenvectors

Interpretation of the factors

PCA Set-up and Interpretation of Factors

• Number of variables to use: must have an excess of samples over variables for stable results.

– 30 VOCs considered suitable for this study.– Selection criteria for a VOC:

1. At least 50% of samples >LDL detection limit

2. Substances reported to NPRI

3. Biogenics

4. Average concentrations

• Sites B and D (Site F – Elk Island National Park had too many values < LDL)

• Interpret factors with eigenvalues > 1 Used 3 corroborating tests (and re-ran PCA): carbon monoxide

from Edmonton and Fort Saskatchewan; wind direction; seasonal split.

PCA Results: Site B

F1 F2 F3 F4 F5

Initial Eigenvalue 14 4 3 2 1

% of Variance 43 17 12 5 4

Cumulative % 43 60 72 77 82

Factor 1 accounts for 43% of the variance

Compounds loading on F1 with values > 0.5:2-Methylbutane, 2-Methylpentane, 3-Methylhexane, 3-Methylpentane, Benzene, n-Butane, Cyclohexane, Ethylbenzene, n-Heptane, n-Hexane, Isobutane, m,p-Xylene, Methylcyclopentane, o-Xylene, n-Pentane, Propane, Propene, and StyreneLOTS OF COMPOUNDS, DIFFICULT TO INTERPET

PCA Results: Site B, Factor 1

• Corroborating Test – Wind Direction– Result: No change of VOCs on factor, weak SW wind direction

loading

• Corroborating Test – CO from city of Fort Sask and Edmonton

– Result: No change of VOCs on factor, CO of Fort Sask and Edmonton load on F1

• Corroborating Test – Seasonal Split– Some differences to 1,2,4-trimethylbenzene, toluene and m-,p-

and o-xylenes.

• Interpretation: Vehicle and industry sources contributing to this factor, not possible to unambiguously determine whether F1 is vehicle dominated or industry dominated.

PCA Results: Site B

F1 F2 F3 F4 F5

Initial Eigenvalue 14 4 3 2 1

% of Variance 43 17 12 5 4

Cumulative %43 60 72 77 82

Vehicle and Industry Industry related:

Industry VOCs and time series

plot shows potential leak.

Long range transport: stable

halogenated VOCs.

Industry related:1,2-dichloroethane and vinyl chloride.

Seasonal effects:Biogenics and

HCFC-22

Lagrangian-stochastic modeling

• Used a short-range, first order lagrangian stochastic model to investigate the relationship between emissions of 1,2-dichloroethane and the ambient measurements.

• Model operated in a forward dispersion mode in which one unit of 1,2-dichloroethane was released as a fugitive emission at a constant rate from the industrial facility.

• Wind profiles were extracted from the 3-D regional GEM meteorological model at 5 levels: 10m, 40m, 120m, 215m and 325m.

• What modeled emission rate is necessary to obtain the measured concentrations?

Lagrangian-stochastic Results

Lagrangian-stochastic Results

• NPRI Reported Value: 10 kg/h

• L-S Model Result: 50-100 kg/h

• Reasons for the discrepancy:– If modeled wind fields do not match the actual winds, the

resulting model emission rate may be affected. – There are challenges in quantifying fugitive emissions partly

due to: i) the available monitoring technologies, ii) the number of inaccessible components in any given facility, and iii) the calculations used to quantify emissions are based on empirical factors and assumptions which may not be in line with actual conditions.

Note: The manufacture and distribution of 1,2-dichloroethane in the Fort Saskatchewan area ceased in late 2006.

Summary

• VOCs in Fort Saskatchewan:– 142 of 150 VOCs were below the Canadian cities’

Group Average.– The majority of the variance in the VOC

concentrations is attributed to a combination of vehicle and industry related emissions.

– Lagrangian-stochastic modeling showed a discrepancy between the reported 1,2-dichloroethane and the modeled emission rate. This may be attributed to either the limitations in the model due to differences in wind profiles and/or to the limitations in quantifying fugitive emissions.