Effect of petrochemical industrial emissions of reactive alkenes and NOx on tropospheric ozone ...

24 Pages·2003·1.37 MB·English

JOURNAL OF GEOPHYSICAL RESEARCH, VOL.108, NO.D8,4249, doi:10.1029/2002JD003070, 2003
Effect of petrochemical industrial emissions of reactive alkenes and
NO on tropospheric ozone formation in Houston, Texas
x
T. B. Ryerson, M. Trainer, W. M. Angevine,1 C. A. Brock,1 R. W. Dissly,1,2
F. C. Fehsenfeld,1 G. J. Frost,1 P. D. Goldan, J. S. Holloway,1 G. Hu¨bler,1
R. O. Jakoubek, W. C. Kuster, J. A. Neuman,1 D. K. Nicks Jr.,1 D. D. Parrish,
J. M. Roberts, and D. T. Sueper1
AeronomyLaboratory,NationalOceanicandAtmosphericAdministration,Boulder,Colorado,USA
E. L. Atlas, S. G. Donnelly, F. Flocke, A. Fried, W. T. Potter, S. Schauffler, V. Stroud,
A. J. Weinheimer, B. P. Wert, and C. Wiedinmyer
AtmosphericChemistryDivision,NationalCenterforAtmosphericResearch,Boulder,Colorado,USA
R. J. Alvarez,1 R. M. Banta, L. S. Darby,1 and C. J. Senff1
EnvironmentalTechnologyLaboratory,NationalOceanicandAtmosphericAdministration,Boulder,Colorado,USA
Received23October2002;revised8January2003;accepted9January2003;published25April2003.
[1] Petrochemical industrial facilities can emit large amounts of highly reactive
hydrocarbons and NO to the atmosphere; in the summertime, such colocated emissions
x
are shown to consistently result in rapid and efficient ozone (O ) formation downwind.
3
Airborne measurements show initial hydrocarbon reactivity in petrochemical source
plumes in the Houston, TX, metropolitan area is primarily due to routine emissions of the
alkenes propene and ethene. Reported emissions of these highly reactive compounds are
substantially lower than emissions inferred from measurements in the plumes from these
sources. Net O formation rates and yields per NO molecule oxidized in these
3 x
petrochemical industrial source plumes are substantially higher than rates and yields
observedinurbanorruralpowerplantplumes.Theseobservationssuggestthatreductions
in reactive alkene emissions from petrochemical industrial sources are required to
effectively address the most extreme O exceedences in the Houston metropolitan
3
area. INDEXTERMS: 0345AtmosphericCompositionandStructure:Pollution—urbanandregional
(0305); 0365AtmosphericComposition andStructure:Troposphere—compositionandchemistry; 0368
AtmosphericComposition andStructure:Troposphere—constituent transport andchemistry; KEYWORDS:
Houstonozoneformation, petrochemical alkeneemissions
Citation: Ryerson,T.B.,et al.,Effect ofpetrochemicalindustrialemissions ofreactivealkenes andNO on troposphericozone
x
formation inHouston,Texas, J.Geophys.Res., 108(D8),4249,doi:10.1029/2002JD003070,2003.
1. Introduction and magnitude of O production consistently occur in
3
plumes downwind of different anthropogenic source types,
[2] Ozone (O3) is formed in the troposphere by photo- characterized by different NO and VOC emissions rates
chemicalreactionsinvolvingtheoxidesofnitrogenNOand x
and the VOC/NO ratios that result [e.g., Daum et al.,
NO (summed as NO ) and reactive volatile organic com- x
2 x 2000a; Gillani et al., 1998; Luria et al., 2000; Neuman et
pounds (VOCs) [Crutzen, 1979; Haagen-Smit, 1952;
al., 2002; Nunnermackeret al., 2000; Ryerson et al., 1998,
Leighton, 1961; Levy, 1971]. Model studies have shown
2001].
that O formation rates and yields are dependent upon both
3 [3] Three anthropogenic source types with contrasting
theabsoluteconcentrationsofNO andVOCsanduponthe
x emissions rates and VOC/NO ratios are fossil-fueled elec-
ratiosofthesespecies[e.g.,DerwentandDavies,1994;Liu x
tricpowerplants,thetransportationsourcestypicalofurban
etal.,1987;Sillman,2000].Resultsfromambientmeasure-
areas, and the petrochemical industry. The first two com-
mentshaveconfirmedthatsubstantialdifferencesintherate
bined account for approximately 75% of total U.S. anthro-
pogenicNO emissionsannually[EPA,2001].Fossil-fueled
x
1AlsoatCooperativeInstituteforResearchinEnvironmentalSciences, electricpowerplantsareveryconcentratedpointsourcesof
UniversityofColorado,Boulder,Colorado,USA. NO but do not emit appreciable amounts of VOCs. Thus
2NowatBallAerospaceCorporation,Boulder,Colorado,USA. x
O production observed in plumes downwind of isolated,
3
rural power plants in the U.S. [e.g., Davis et al., 1974]
Copyright2003bytheAmericanGeophysicalUnion.
0148-0227/03/2002JD003070$09.00 occurs as a result of mixing plume NOx with primarily
ACH 8 - 1
ACH 8- 2 RYERSON ETAL.:PETROCHEMICAL EMISSIONS AND OZONEFORMATION
biogenic reactive VOCs, especially with isoprene [Cha- that project to evaluate the effects of petrochemical indus-
meides et al., 1988; Trainer et al., 1987a, 1987b], over trial emissions on tropospheric O formation. First, we
3
time during plume transport. Measurements confirm the analyze O production in spatially resolved plumes from
3
strong dependence of O production on NO concentration the geographically isolated complexes at Sweeny, Freeport,
3 x
[Gillanietal.,1998;Nunnermackeretal.,2000;Ryersonet and Chocolate Bayou (Figure 1). We then extend this
al.,1998]andonambientVOCconcentrationandreactivity analysis to include data from coalesced plumes downwind
[Luria et al., 2000; Ryerson et al., 2001]. of multiple petrochemical complexes in the heavily indus-
[4] Power plant plume VOC/NOx ratios can be suffi- trialized Houston Ship Channel and Texas City areas.
cientlylowthatO formationisinitiallysuppressedinfavor Finally, O production in petrochemical industrial plumes
3 3
of efficient nitric acid (HNO ) production, removing NO is compared to that observed downwind of urban areas and
3 x
from further participation in O formation cycles [Neuman rural, fossil-fueled electric utility power plants.
3
et al., 2002; Ryerson et al., 2001]. In contrast, the tailpipe
emissions that dominate urban areas are sources of both
2. Experimental Procedure
NO and VOCs. The many small individual sources con-
x
tributingtourbanemissionsareusuallyconsideredtogether [7] The National Center for Atmospheric Research
as an areasource dispersed over tens to hundreds of square L-188C Electra aircraft leased by the National Oceanic
kilometers. As a result, urban plumes are relatively dilute, and Atmospheric Administration (NOAA) was based at
with total NOx emissions rates comparable to those from Ellington Field, Houston, TX, as part of the Texas Air
power plants but dispersed over a much larger area. QualityStudyinAugustandSeptember2000.Instrumenta-
CoemissioninthismannerresultsininitialVOC/NOxratios tion aboard the Electra included 1-Hz measurements of O3,
that favor O3 formation immediately upon emission, typi- nitric oxide (NO), nitrogen dioxide (NO2), HNO3, total
callyleadingtofasterO3productionratesandhigheryields reactive nitrogen (NOy), carbon monoxide (CO), carbon
in urban plumes than in concentrated power plant plumes dioxide(CO ),sulfurdioxide(SO ),andspectrallyresolved
2 2
[Daum et al., 2000a; Luria et al., 1999; Nunnermacker et actinic flux [Holloway et al., 2000; Neuman et al., 2002;
al., 2000]. Nicks et al., 2003; Ryerson et al., 1998, 1999, 2000].
[5] The fastest rates of O3 formation, and the highest Formaldehyde(CH2O)wasmeasuredbytunablediodelaser
yields per NOx molecule emitted, are predicted for con- absorption spectrometry [Fried et al., 1998; Wert et al.,
ditions where strongly elevated concentrations of NOx and 2003] at 10-s resolution for 27 and 28 August, the two
reactiveVOCsaresimultaneouslypresent.Theseconditions flights reported here. Peroxyacyl nitrate compounds (e.g.,
can be routinely found in the NOx- and VOC-rich plumes peroxyacetyl nitrate (PAN)) were measured once every
from petrochemical industrial facilities [e.g., Sexton and 3.5minbygaschromatography(GC)usingelectroncapture
Westberg, 1983]. Petrochemical NOx emissions are a by- detection. GC measurements, either performed in situ
product of fossil-fuel combustion for electric power gen- [Goldanetal.,2000]orasawhole-air sample(WAS) from
eration, for heat generation, and from flaring of unwanted canisters [Schauffler et al., 1999], provided speciated data
volatilematerials;NOxemissionfromalargepetrochemical on an extensive set of VOCs (Table 1). Thirty-nine WAS
facilitycanapproachthatfromalargeelectricutilitypower canisters were sampled on each flight; in addition to the
plant. While a given facility may have hundreds of com- VOCs, the WAS instrument provided data on CO, methane
bustion sources, spread over many square kilometers, the (CH ), C through C monofunctional alkyl nitrate com-
4 1 5
majority of petrochemical NOx emissions typically come pounds (RONO2), and a variety of other halogenated
from onlyafewof thelargestsources.Thus concentrations species.
of NO in plumes from large petrochemical facilities are
x
typically much higher than in those from urban areas. 2.1. Measurement Uncertainties
Sources of VOC emissions from a petrochemical industrial [8] Here we briefly assess uncertainties in the chemical
facilityarethoughttobemuchmorenumerousthansources measurements most relevant to the following analyses.
of NO . VOCs can be emitted via continuous emissions Calibrations of the reactive nitrogen (NO, NO , HNO ,
x 2 3
from stacks, episodic emissions specific to individual pro- PAN compounds, and total NO ) measurements are con-
y
cesses, and leaks from pipes and valving. The wide variety servatively estimated to be accurate to better than ±10%
of VOC compounds typically emitted from petrochemical based on in-flight standard addition calibration data, multi-
facilities, with differing reactivities toward the hydroxyl ple internal consistency checks, and extensive intercompar-
radical (OH), must be considered to understand the O - ison with other aircraft and ground measurements of these
3
forming potential of these sources [Carter, 1994; Derwent, species[Neumanetal.,2002].Inadditiontouncertaintiesin
2000; Watson et al., 2001]. calibration, estimated imprecision for the 1 Hz reactive
[6] The greater Houston, TX, metropolitan area is distin- nitrogenmeasurementsatlowmixingratiosvariedbetween
guished by the largest concentration of petrochemical ±20partspertrillionbyvolume(pptv)forNOto±150pptv
industrial facilities in the U.S. (Figure 1). Further, Houston for NO. Both the NO chemiluminescence instrument and
y y
is noted for some of the highest O mixing ratios routinely theHNO chemicalionizationmassspectrometerhavebeen
3 3
encounteredinthecontinentalU.S.inthepresent-day.Asa shown to sample atmospheric HNO rapidly and quantita-
3
result, photochemical O and aerosol production in the tively during flight [Neuman et al., 2002; Ryerson et al.,
3
Houston area was the focus of the Texas Air Quality Study 2000]. Tight correlation (r2 = 0.962), a linear least squares
2000 field project [Brock et al., 2003; Kleinman et al., fitted slope of 0.96 ± 0.05, and an intercept of 22 pptv
2002; Neuman et al., 2002; Wert et al., 2003]. We report suggeststhatnosystematicbiasexistedbetweenthesumof
measurements taken from an instrumented aircraft during (NO+NO +HNO +PAN)compoundsandthetotalNO
2 3 y
RYERSON ETAL.:PETROCHEMICAL EMISSIONS AND OZONEFORMATION ACH 8 - 3
Figure1. A200(cid:1)200kmmapcenteredonthegreaterHoustonmetropolitanarea(redline),showing
the study region for Electra research flights of 27 and 28 August 2000. Locations of point emission
sources are shown sized according to volatile organic compound emission source strengths (‘‘E ,’’
VOC
filled green circles) and NO emission source strengths (‘‘E ,’’ open black circles) according to the
x NO
x
legends provided. Emissions data are taken from the 2000 Texas Natural Resource Conservation
Commission point source database; only sources greater than 100 t/yr are shown. The Houston Ship
Channel is east of the Houston urban center, surrounded by numerous petrochemical facilities at 29.7(cid:1)
latitude; other major petrochemical complexes and power plants are labeled.
measurement over the course of the field mission [e.g., components of the reactive nitrogen family were measured
Neuman et al., 2002]. The fractional contribution of C -C accurately.
1 5
RONO2 compounds (measured in the WAS) ranged [9] Comparison of the two independent CO measure-
between 0.01 and 0.02 of total NO, similar to or slightly ments aboard the Electra (GC analysis of WAS canisters
y
lowerthanpreviousstudies[Bertmanetal.,1995;Flockeet [Schauffler et al., 1999] and vacuum-ultraviolet resonance
al., 1991; Ridley et al., 1997]. Although coincident alkyl fluorescence [Holloway et al., 2000]) showed tight correla-
nitrate and PAN data are very sparse, inclusion of the tion (r2 = 0.989), a fitted linear least squares slope of 1.03,
averageRONO fractionof 0.015intheabove NO budget and an intercept of 4 parts per billion by volume (ppbv),
2 y
brings the sum very close to 1, indicating that all the major suggesting that both instruments measured ambient CO to
ACH 8- 4 RYERSON ETAL.:PETROCHEMICAL EMISSIONS AND OZONEFORMATION
Table1. NamesandOHRateCoefficients(k )forHydrocarbonCompoundsandSelectedOtherSpeciesMeasuredAboardtheElectra
OH
Used inThisReporta
Alkanes k Alkenes k Aromatics k Alkynes k Others k
OH OH OH OH OH
Ethane 0.3 ethene 9 benzene 1.2 ethyne 0.9 CO 0.2
Propane 1.1 propene 26 methylbenzene(toluene) 6.0 propyne 5.9 CH 0.007
4
n-Butane 2.4 1-butene 31 ethylbenzene 7.1 CHCHO 17
3
2-Methylpropane 2.2 cis-2-butene 56 1,2-dimethylbenzene 13.7 CHO 8
2
n-Pentane 4.0 trans-2-butene 64 1,3-and1,4-dimethylbenzene 20 NO 9
2
2-Methylbutane 3.7 1,3-butadiene 67 phenylethene(styrene) 58
Cyclopentane 5.0 1-pentene 31 2-methylethylbenzene 12.3
n-Hexane 5.5 2-methyl-2-butene 87 n-propylbenzene 6.0
2-Methylpentane 5.3 3-methyl-1-butene 32 1,3,5-trimethylbenzene 58
2,2-Dimethylbutane 2.3 trans-2-pentene 67 1,2,4-trimethylbenzene 33
2,3-Dimethylbutane 6.0 cis-2-pentene 65 1,2,3-trimethylbenzene 33
3-Methylpentane 5.4 cyclopentene 67
Methylcyclopentane 5.7 2-methyl-1,3-butadiene 101
(isoprene)
Cyclohexane 7.2
n-Heptane 7.0
2-Methylhexane 7.0
3-Methylhexane 7.5
2,3-Dimethylpentane 7.1
2,4-Dimethylpentane 5.0
Methylcyclohexane 10.0
n-Octane 8.7
2,2,4-Trimethylpentane 3.6
cis-andtrans-1, 9.5
3-Dimethylcyclohexane
n-Nonane 10.0
n-Decane 11.2
aNormaltypeindicatescompoundsmeasuredonlyinthewhole-aircanistersamples,italicizedtypeindicatesthosemeasuredonlyintheinsituGC,and
boldtypeindicatesthosemeasuredinbothsystems.Ratecoefficients(k ,inunitsof10(cid:2)12cm3molec/s)calculatedfor298Kand1013mbfromdatain
OH
theworkofAtkinson[1994,1997]andDeMoreetal.[1997].CO,CH,NO,CHO,andCHCHOareincludedforcomparison.
4 2 2 3
within the stated uncertainties of the two techniques [Nicks mixed layer is derived from on-board chemical and mete-
et al., 2003]. The CH O measurement has been critically orological measurements [Ryerson et al., 1998] and obser-
2
evaluated to characterize its time response, precision, and vations from other airborne [Senff et al., 1998] and
accuracy, and the data were compared to a ground-based ground-based[Angevineetal.,1994]remote-sensinginstru-
long-pathmeasurementusingdifferentialopticalabsorption mentation deployed throughout the area for the Texas 2000
spectroscopy (DOAS) [Stutz and Platt, 1997]. These tests study. Uncertainties in wind speeds of ±1 m/s and in
suggestthe10-sCH OdataonboardtheElectraareaccurate boundarylayerheightsof±10%areestimatedbycomparing
2
tobetterthan±(120pptv+10%)[Wertetal.,2003].The1-s derived values from the various aircraft- and ground-based
O measurement by NO-induced chemiluminescence was data sets. Tabulated information on source emissions was
3
compared to a UV-absorption measurement aboard the obtained from and, where possible, crosschecked between
Electra, and to a separate UV-absorption measurement various inventory databases. These included the U.S. Envi-
during overflights of an instrumented ground site, and ronmentalProtectionAgency(EPA)AIRS,TRI,andE-Grid
shown to be accurate within the stated uncertainty of databases (www.epa.gov/ttn/chief), as well as from infor-
±(0.3 ppbv + 3%). VOC data were compared between the mation provided by plant operators to the Texas Natural
WAS measurements and the in situ GC and found to be ResourceConservationCommission(TNRCC)forthe2000
accurate, within stated experimental uncertainties of ±10% reporting year (www.tnrcc.state.tx.us/air/aqp/psei.html).We
or less, for the compounds reported here at the elevated use the TNRCC point source database (PSDB) for 2000 as
mixing ratios relevant to this report. Generally, the uncer- the primary reference in this report. Hourly averaged
tainty of the SO measurement was within ±10% for SO emissions data, from continuous emission monitoring sys-
2 2
levels well above the detection limit of approximately 0.5 tems (CEMS) and from estimates provided by facility
ppbv. However, for the data on the two flights presented operators, were also examined for the time periods of the
here,thisaccuracywassporadicallydegradedbyshort-term presentstudy.Thetimingandnatureofnonroutine-emission
transients, of up to several parts per billion by volume, due events, or upsets, at many facilities was also reported to
to operational difficulties with the in-flight calibration TNRCC and are taken into account in the present analysis.
system.TheSO dataareusedhereonlyinarelativesense,
2 2.3. Plume Identification
e.g., to distinguish between different anthropogenic source
typesbynotingthepresenceorabsenceofelevatedSO ina [11] Plumes from different sources are distinguished by
2
given plume. markedly different enhancements above background of
many of the chemical species measured aboard the Electra
2.2. Meteorological and Emissions Data aircraft,reflectingthedifferentemissionsprofilesfromeach
[10] Information on wind speed and direction, mixed source type. Fossil-fueled electric utility power plant
layer heights, and vertical mixing within and above the plumesshowrelativelystrongenhancementsinNO species
y
RYERSON ETAL.:PETROCHEMICAL EMISSIONS AND OZONEFORMATION ACH 8 - 5
andCO .SO canalsobestronglyenhancedinpowerplant We analyze data from these days specifically because the
2 2
plumes if sulfur-rich fuels are used and emissions are not prevailing wind direction provided spatially separated and
treated to remove it; typically,coal- and oil-fired units emit relatively well-resolved plumes from several isolated pet-
substantial amounts of SO , while natural-gas-fired turbine rochemicalindustrialfacilities,theW.A.Parishpowerplant,
2
units do not. CO enhancements are typically negligible in themultiplepetrochemicalcomplexesalongtheShipChan-
power plant plumes, with some exceptions [Nicks et al., nel, and the urban core of Houston itself.
2003]. Substantial VOC enhancements in power plant [14] We present data on photochemical O3 production
plumes are never detected. Urban plumes are characterized from emissions released during the morning and early
by substantial enhancements in CO and VOCs, typical of afternoon hours and observed within 15 min to ca. 8 hours
tailpipe combustion sources [Harley et al., 2001]; NO following release. These findings are most relevant to
y
species and CO are also enhanced but to a lesser degree typical Houston summertime conditions characterized by
2
than in power plant plumes. SO is not typically substan- low to moderate background O levels (40–60 ppbv)
2 3
tially enhanced in urban plumes. Plumes from petrochem- coupled with substantial and rapid O production (within
3
ical complexes have varied chemical composition, but 4 hours of release) in a single day. This characteristic is
typically have enhanced NO and CO characteristic of uniquetoHoustonandisincontrasttootherurbanareasin
x 2
the embedded power plants required to supply electricity the U.S., in which the highest O mixing ratios typically
3
and heat to the facilities. Petrochemical plumes can also be result from slower accumulation of O over the period of
3
characterized by elevated CO levels and elevated SO several days [e.g., Banta et al., 1998; Daum et al., 2000b;
2
depending on the fuel source. Enhanced VOC levels spe- Kleinman et al., 2000; Winner and Cass, 1999].
cifictoindividualprocessesandfacilitiesarealsocharacter-
istic of petrochemical source plumes [Watson et al., 2001]. 3.1. Isolated Petrochemical Industrial Complexes
Thus examination of the chemical data in conjunction with [15] Aircraft flights on 27 and 28 August 2000 sampled
aircraft position, wind speed, and wind direction informa- the spatially resolved plumes from several isolated petro-
tion permits identification of plumes from different sources chemicalcomplexessouthoftheHoustonmetropolitanarea
until they are nearly fully mixed with each other or with (Figure2).These plumeswerecomposed oftheaggregated
background air. emissions from groupings of chemical plants in well-segre-
[12] Plume chemical and dynamic evolution was tracked gated areas several kilometers in extent. On both days,
from the Electra aircraft by performing crosswind transects emissionsplumesfromcomplexesatSweeny,Freeport,and
withinthemixedlayeratsuccessivedistancesdownwindof ChocolateBayouwerecarriedinlandbysteadywindsat4.5
individualsourcesandsourcecomplexes[e.g.,Brocketal., ±1.0m/sat160(cid:1)±16(cid:1)fromtheGulfofMexico.Measure-
2003;Ryersonetal.,1998].Thesedataweretakenbetween ments upwind over the Gulf onboth days characterized the
noon and 1700 hours local standard time, at times of day inflowasrelativelyclean,devoidofappreciableamountsof
when mixing was most rapid, so that compounds emitted reactiveVOCsorNO ,withCOlevelsbelow100ppbvand
x
from a source were rapidly and extensively mixed within O roughly 35 ppbv. For the isolated sources, we establish
3
the boundary layer. Emissions from an individual petro- thatthesourceofenhancedplumelevelsofNO andVOCs,
x
chemical complex are treated as coming from asingle or at and the O and other photoproduct formation, are due to
3
mostafewpointemittersfortransectsperformed>10kmor emissionsfromthepetrochemicalfacilitiesthemselves.The
a few source diameters downwind [Wert et al., 2003]. This plume transect data are then used to estimate VOC/NO
x
is justified by downwind observations of multiple Ship emissions ratios, NO oxidation rates, HNO production
x 3
Channel point source plumes on these two flight days; rates, net O production rates and yields, and to determine
3
originallyseparatedplumes becamemutuallyindistinguish- the primary species contributing to OH reactivity in these
ablebetweensuccessiveafternoontransects15kmapart,or petrochemical emissions plumes.
roughly an hour of transport time downwind. 3.1.1. Emissions Sources
[16] Enhancements of NOx, CO, CO2, and VOCs, and
secondary photoproducts including O , CH O, CH CHO,
3. Results 3 2 3
andPANcompounds,observedintheseisolatedplumescan
[13] Hourly averaged O3 mixing ratios measured at sur- be unambiguously attributed to emissions from the petro-
face sites can exceed 200 ppbv during severe summertime chemical facilities at each location. Potential emissions of
pollution episodes in the Houston metropolitan area. Pre- NO andreactivehydrocarbonsfromcolocatedautomobile,
x
vious studies in Houston have suggested these extreme O truck, ship, and rail traffic in the area are ruled out as
3
exceedences are more common on days characterized by significantcontributorstothetotalsemittedfromthesethree
relatively complex meteorological conditions and can be complexes. The fraction of on-road transportation, or tail-
frequentduringstagnationepisodes[Davisetal.,1998].For pipe, emissions from automobiles and trucks is expected to
Sunday,27August,andMonday,28August2000,however, have been minimal owing to the location of these com-
no exceedence of the 1 hour, 120 ppbv Federal air quality plexes, which are remote from city or town centers and are
standard was recorded in the Houston metropolitan area, in characterized by low roadway densities in all three source
part due to steady ventilation by relatively clean southerly areas (Figure 1). Recent reports suggest that such tailpipe
winds from the Gulf of Mexico. Despite relatively low O emissions result in tightly correlated enhancements in CO
3
mixingratioenhancements,Electraresearchflightsonthese and NO , with characteristic morning emissions ratios in
x
2 days provided data from which O formation rates and 2000 of roughly 5–6 (mol CO/mol NO ) [Harley et al.,
3 x
yields downwind of different anthropogenic source types 2001; Parrish et al., 2002]. These values are in good
are determined under relatively uniform-flow conditions. agreement with tailpipe CO/NO emissions ratios of 6 ± 1,
x
ACH 8- 6 RYERSON ETAL.:PETROCHEMICAL EMISSIONS AND OZONEFORMATION
ured in plume transects within 10 km of the three isolated
petrochemicalcomplexesvaried,rangingfrom0.1tonearly
1, further illustrating that the NO was not emitted from
x
tailpipe sources.
[17] Ratios of hydrocarbons to ethyne (acetylene; C2H2)
measuredinplumetransectsalsoruleouttailpipesourcesas
substantialcontributorstotheobservedenhancementsinthe
isolated petrochemical facility plumes. Tailpipe emissions
have characteristic ratios of (ethene (C H )/ethyne) ranging
2 4
from 1 to 3 and (propene (C H )/ethyne) from 0.5 to 1.5,
3 6
determined from airborne VOC measurements above the
urbancoresofNashville,TN,andAtlanta,GA,in1999,and
inHoustonandDallas,TX,in2000.Atmosphericoxidation
processes decrease these two ratios over time between
emission and measurement, primarily due to the substan-
tiallyfasterOHreactionratecoefficientsofC H andC H
2 4 3 6
comparedtoethyne(Table1).Nonetheless,theratiosinthe
urbanplumesobservedfrom aircraft arein goodagreement
with recent tunnel measurements in both Houston (W.
Lonneman,unpublisheddata,2000)andinNashville [Har-
ley et al., 2001]. In contrast, observed molar ratios in near-
fieldtransectsoftheplumesfromavarietyofpetrochemical
facilities in the Houston study region for (C H /ethyne)
2 4
ranged from 10 to 30 and for (C H /ethyne) from 5 to 40.
3 6
These values are substantially higher than ratios from
tailpipesources,confirmingthatthecontributionofalkenes
from tailpipe sources was negligible in these plumes.
[18] Fortheisolatedfacilities,theabsenceofsubstantially
elevated SO in these plumes is characteristic of gas-fired
2
turbine exhaust and suggests that locomotive and marine
diesel emissions, which are typically rich in SO [Corbett
2
andFischbeck,1997],arenotsignificantsourcesofNO in
x
the plumes studied here. Small enhancements of SO
2
observed in the Freeport plume are qualitatively consistent
with emissions from the Gulf Chemical and Metallurgical
Plant, a known SO source within the Freeport complex
2
[Brock et al., 2003]. We conclude the observed plume
enhancements are due to emissions of reactive VOC and
NO directly from the petrochemical facilities themselves.
x
[19] While other colocated sources are ruled out as
substantial contributors to the isolated petrochemical
plumes, these plumes may have entrained emissions from
other sources during transport. For example, the wind
direction on the 2 days considered here advected the
Sweeny plume over a wooded area to the north-northwest,
which is a known weak biogenic source of isoprene
Figure2. A90(cid:1)90kmdetailviewofthemapshownin
[Wiedinmyeret al., 2001]. This acted to continually replen-
Figure 1, showing measured ozone and NO values plotted
y ish the Sweeny plume with low but nonnegligible amounts
relative to aircraft position along the SW portions of the
ofisopreneduringtransport.Plumesfromthepetrochemical
flight tracks on 27 August (first panel) and 28 August
complexes south of Houston, as well as that from the W.A.
(secondpanel).Symbolsalongtheflighttracksgivesample
Parish power plant, eventually were transported over the
locations for the whole-air canisters (WAS, open squares)
westernandsouthernedgesoftheHoustonurbanarea,with
and in situ gas chromatography (barred squares). Winds on
additional mixing of urban tailpipe emissions into the aged
bothdaysweresteadyfrom 160(cid:1)at4.5m/s.The scalebars
plumes. The overall impact of entrainment during transport
show a 20 ppbv equivalent enhancement in ozone.
onderivedNO oxidationrates,andplumeproductionrates
x
of O and other secondary products, is shown below to be
3
estimated from Electra data taken in late-morning transects relatively minor.
of the Houston urban core. In contrast, for transects flown 3.1.2. VOC Reactivity
very close to the isolated petrochemical facilities, observed [20] WAS canisters taken in resolved plumes from the
enhancementsofthesespecieswereoftenpoorlycorrelated, threeisolatedpetrochemical complexesshowelevated mix-
suggesting physically separate emissions of CO and NO ingratiosofmanyofthemeasuredhydrocarbons(Table1),
x
uncharacteristic of tailpipe sources. CO/NO ratios meas- including substantial enhancements in alkanes, alkenes,
x
RYERSON ETAL.:PETROCHEMICAL EMISSIONS AND OZONEFORMATION ACH 8 - 7
aromatics, and ethyne. In general, the compounds ethane tinued beyond the final aircraft transect downwind ((cid:3)60
(C H ),C H ,propane(C H ),C H ,andisomersofbutane km), catalyzed by the remaining NO , additional NO from
2 6 2 4 3 8 3 6 x x
andpentanewerethemostabundant,withdifferingrelative other downwind sources, and that recycled from thermal
abundances characteristic of the three source complexes. decomposition of PAN-type compounds. However, the
However, the contribution of an individual hydrocarbon remaining alkanes will oxidize relatively slowly thereafter,
species to prompt O formation is determined both by its and alkane reaction products are predominantly the less-
3
concentration and by how rapidly that compound can react reactive ketones [Atkinson, 1997]. Given the low observed
with OH, which is the rate limiting step in O formation mixing ratios of NO and reactive VOC remaining at these
3 x
[e.g., Atkinson, 1994, 1997; DeMore et al., 1997]. Alkenes distances, andthe observeddecreasein O production rates
3
and larger aromatic compounds typically have relatively betweensuccessivetransects,therateatwhichO wouldbe
3
large OH rate coefficients (Table 1); thus these compounds formed is also expected to be substantially lower down-
will contribute more to prompt O production at a given wind. The evolution over time of plume CH O mixing
3 2
concentration thanwillalkanesor alkynes. Toelucidate the ratios [Wert et al., 2003] further suggests that reservoirs of
directly emitted VOCs primarily responsible for plume O compounds serving as precursors to peroxy radical forma-
3
formation, the hydrocarbon data are presented in Figure 3 tion in the plumes were also relatively depleted at these
by multiplying the concentration of each measured species distances.ThusO formationdownwindofthefinalElectra
3
by the appropriate OH rate coefficient at the measured transects (plume ages >4 hours) in the isolated petrochem-
ambient temperature and pressure. The black horizontal ical plumes is expected to have been relatively minor
bars in Figures 3a and 3c show total OH reactivity calcu- compared to that observed on the timescales considered
lated from the measured VOCs, excluding the photoprod- here. The majority of O produced in these plumes is
3
ucts CH O and acetaldehyde (CH CHO). While plume OH therefore ascribed to colocated emission of large amounts
2 3
reactivities due to NO , CH , and CO are not negligible of C H and C H with NO from the isolated petrochem-
2 4 2 4 3 6 x
(Figures 3a and 3c), the large increases over reactivities ical facilities.
calculatedfromsamplestakenoutsidetheplumesarealmost [23] Equally important in designing an effective O3
entirely due to petrochemical VOC emissions. Further control strategy is the identification of VOC compounds
examination of the individually speciated VOC data shows that did not contribute significantly to OH reactivity, and
that of the many compounds emitted and measured, two thus prompt O formation, in the isolated plumes. While
3
compounds alone account for the majority of the plume mixing ratios of many alkane compounds were enhanced,
reactivityabovethebackground.ThedatainFigures3band sometimes strongly, these contributed negligibly to O
3
3d from both days show that the principal reaction partners formation in the Freeport and Sweeny plumes on these
forOHinallthreeplumeswerethedirectlyemittedalkenes timescales due to their substantially lower OH reaction
C H and C H andtheir oxidation products. Mixing ratios rates. An exception is noted for the Chocolate Bayou
2 4 3 6
of C H and C H observed within 5 km of these sources plume,inwhichisobutanemixingratiosexceeding20ppbv
2 4 3 6
exceeded background levels by factors ranging from 20 to were measured 5 km downwind, accounting for 11% of
over 200. Elevated plume levels of the reactive alkenes OH reactivity with the measured VOC compounds at this
C H and C H and their photooxidation products CH O distance. Alkenes other than C H and C H contributed
2 4 3 6 2 2 4 3 6
and CH CHO are sufficient to dominate OH reactivity for little to initial OH reactivity. While the OH rate coefficient
3
sometimeafteremission.Forexample,inthe(cid:3)20-min-old for1,3-butadieneisafactorof(cid:3)3largerthanthatforC H
3 6
Chocolate Bayou plume sampled at 1902 UT (1302 hours (Table 1), emissions of 1,3-butadiene contributed relatively
local time) on 27 August (Figure 3a), C H and C H little to OH reactivity in these plumes, even after account-
2 4 3 6
account for >80% of the OH reactivity calculated from ing for differential loss in samples taken within 10 km of
themeasuredhydrocarbons(Table1).Eveninthe(cid:3)45-min- the Freeport and Chocolate Bayou facilities. All other
oldFreeportplume,C H andC H stillaccountfor75%of directly emitted and individually measured VOCs contrib-
2 4 3 6
OH reactivity. uted less than 0.2/s to the OH loss rate, and, to first
[21] As these alkenes are rapidly consumed, their photo- approximation, can be neglected in terms of prompt O3
products CH O and CH CHO increase in relative impor- formation. This finding includes the suite of higher aro-
2 3
tanceasOHpartners,actingtofurtherpropagatetheradical matic compounds measured (Table 1), which, like 1,3-
chain leading to O formation. Measurements of plume butadiene,areveryreactive,butwerepresentatsufficiently
3
CH O show that direct emissions of this compound are low levels to be minor contributors to rapid O formation
2 3
negligibly small compared to CH O formed during trans- in the plumes presented here. Thus relatively few com-
2
port from the OH-induced oxidation of the directly emitted pounds were responsible for the bulk of initial VOC
VOCs, primarily C H and C H [Wert et al., 2003]. The reactivity of these petrochemical plumes, which were
2 4 3 6
CH O derived from alkene oxidation, once formed, con- dominated for the first 50 km of transport (first 2–3 hours
2
stitutesamajorreactionpartnerforOHinalltheseplumes, after emission) by anthropogenic emissions of C H and
2 4
and photolysis of CH O becomes an important free radical C H and by the aldehyde photoproducts derived from
2 3 6
source.CH OandCH CHOarethemselvesrelativelyshort- these species. Enhancements in initial plume OH reactivity
2 3
lived, and within hours the longer-lived alkane compounds duetoCOandNO emissionswerenegligiblecomparedto
2
are observed to dominate plume reactivity downwind. theenhancementsresultingfromalkeneemissions(Figure3).
However, by then, the shorter-lived NO had already been Considering the wide variety of VOCs emitted from petro-
x
extensively oxidized. chemical industrial sources [Derwent, 2000], this finding
[22] The presence of elevated mixing ratios of longer- suggests a relatively straightforward O3 control strategy.
lived alkanes suggests that O formation may have con- Reducingemissionofthesetwoalkenesisclearlyindicated
3
ACH 8- 8 RYERSON ETAL.:PETROCHEMICAL EMISSIONS AND OZONEFORMATION
Figure3. (a)Timeseriesof chemical data fromthe aircraft transect at29.3(cid:1) latitude(Figure2),which
sampled plumes downwind of the Sweeny,Freeport,and Chocolate Bayou petrochemical complexes on
27 August 2000. Horizontal bars show the time, duration, and calculated value of k X[NO ] (green
OH 2
bars), k X[CO] (gray bars), k X[CH ] (blue bars), and k X(cid:1)[VOC] (black bars) for each
OH OH 4 OH
hydrocarbon sample. (b) Speciated hydrocarbon measurements show that the alkenes ethene, propene,
and isoprene account for >80%, and the sum of all measured aromatics <3%, of total plume OH
reactivities with hydrocarbons on this transect. Derived loss rates for all measured volatile organic
compounds(VOC)areplotted;notethatmostliebelowtheminimumyaxisvalueof0.1/s.CH Omixing
2
ratios (blue circles) were sufficiently enhanced, primarily due to photoproduction from directly emitted
alkenes,torepresentasubstantialreactionpartnerforOHintheseplumes.(candd)AsinFigures3aand
3b above, for the 29.3(cid:1) latitude transect of the 28 August flight.
RYERSON ETAL.:PETROCHEMICAL EMISSIONS AND OZONEFORMATION ACH 8 - 9
Figure 3. (continued)
as the most effective VOC-reduction strategy to minimize reactionorphysicalremovalratesdifferforthetwospecies
promptO formationdownwindofthesesources. in question. We use plume transect data to estimate the
3
3.1.3. (Alkene/NO ) Emission Ratios emissions ratios of (C H /NO ) and (C H /NO ) for the
x 2 4 x 3 6 x
[24] Ratios of coemitted species from a single large Sweeny, Freeport, and Chocolate Bayou facilities, account
source are, to first order, independent of dilution over time for differential chemical loss with respect to OH, and
during transport downwind and are given by the slope of a compare to emissions ratios calculated from the 2000
linear fit to measured data. Ratios measured downwind in TNRCC PSDB inventory. We note that some differences
plumes will differ from the emissions ratio if chemical existbetweenthe1999inventoryusedbyWertetal.[2003],
ACH 8- 10 RYERSON ETAL.:PETROCHEMICAL EMISSIONS AND OZONEFORMATION
Table2. TabulatedNO andAlkeneEmissionsRatesandRatios,andMeasurement-InferredEmissionRatios,forSelectedPetrochemical
x
Complexes andanElectric UtilityPower Plant
Tabulated Measured Tabulated Measured
Complex E a E a Ethene/NO Ethene/NO E a Propene/NO Propene/NO
NOx ethene x x propene x x
Sweeny 12.6 0.6 0.05 3.6 0.4 0.03 2.0
Freeport 34.8 1.8 0.05 1.5 0.4 0.01 0.5
ChocolateBayou 7.2 0.6 0.08 2.0 0.7 0.10 4.0
W.A.Parish 66.5 ... ... ... ... ... ...
aSumofannuallyaveragedemissions(kmol/h)listedinthe2000TNRCCPSDBfortheboxesinFigure1.
andthe2000inventoryusedinthepresentwork,whichhas reportedbythelargestofthefourfacilitiesintheChocolate
only recently become available, for the Texas 2000 study Bayou area differed by less than 5% for the 27 and 28
period.Theseinventorytabulationsarenotstaticovertime, August plume study periods reported here. Further, very
reflecting changes in operating conditions, plant activity, little variation is apparent over the 11 days of hourly
and addition of new facilities or shutting down older units. averaged emissions rates for NO (264 consecutive hours,
x
Changes from the 1999 to the 2000 inventory are also due average ± sigma = (7.9 ± 0.2), max = 8.5, min = 7.5, with
to a substantially smaller fraction of VOC emissions units of 1023 mol/s) reported by this facility (22 August–1
reported as ‘‘unspeciated’’ in 2000. The PSDB inventory September 2000, including the plume study periods). The
is the basis for the predictive and regulatory modeling by 2000PSDBannuallyaveragedNO emissionsrateisfurther
x
TNRCC and EPA. consistent within 15% with that derived from the hourly
[25] (C2H4/NOx)ratiosmeasuredintransectswithin5km averages from this facility. In addition, the available daily
of the Freeport and Chocolate Bayou facilities were not averaged NO emissions data from the second largest
x
significantly affected by differential chemical or physical facility show variations of less than 10% (11 consecutive
removal; the inferred emissions ratios are therefore judged days, average ± sigma = (2.7 ± 0.2), max = 3.0, min = 2.5,
to be accurate to within the combined measurement uncer- with units of 1023 mol/s). Annual averages suggest these
tainties of ±17%. The closest Sweeny plume transects took two facilities account for 91% of the total NO emissions
x
place ca. 22 km or 1.4 hours downwind; given the larger fromtheChocolateBayousourceregion.Similararguments
OH reaction rate for C H relative to NO (Table 1); the can be constructed for the facilities in the Sweeny and
3 6 x
resultingestimated(C H /NO )emissionsratioissubjectto Freeport source regions (Figure 1). These findings suggest
3 6 x
the largest uncertainty.We judge the estimated (C H /NO ) that for the 27 and 28 August plume studies, the emissions
3 6 x
emissions ratio for Sweeny is only accurate to within a ratesderivedfromhourly,daily,andannuallyaveragedNO
x
factorof2.Theseestimatedemissionsdataarepresentedin inventories are comparable, and that NO emissions from
x
Table 2 along with the ratios calculated from annual the three isolated petrochemical source regions were quite
emissions rates listed in the 2000 PSDB inventory for the constant and representative of normal operating conditions
geographicsourceareasgivenbytherectanglesinFigure1. of these complexes.
The data in Table 2 show that substantial discrepancies, 3.1.3.2. NO Emissions are Well Represented
x
many times larger than the measurement uncertainty, exist by the Available Inventories
betweenthemeasurement-inferredemissionratiosandthose [28] The overall accuracy of the NOx emissions rates for
calculated from the 2000 inventory values. Small differ- these three complexes is evaluated by comparing to emis-
ences in the inventory (alkene/NO ) ratios between Table 2 sionsratesinferredfromplumemassfluxofNO,calculated
x y
in this report and those in Table 4 of Wert et al. [2003] are from near-field aircraft transect data [Brock et al., 2003;
due to the different inventory reporting years. Ryersonetal.,1998,2001;Traineretal.,1995;Whiteetal.,
[26] Suchlargediscrepanciescouldarisefrominaccuracy 1976], to the available inventory values. Mass flux esti-
either in the tabulated inventory values of NO , of alkenes, mates from aircraft data taken in well-resolved plumes are
x
orofboth,forthepetrochemicalcomplexesinquestion.The subject to several sources of uncertainty, including deposi-
discrepancy could also arise if the actual NO emissions tional losses, venting to the free troposphere, incomplete
x
were extremely low, or the alkene emissions extremely mixing within the boundary layer, and variability in wind
high, from all three facilities simultaneously during both speeds. These uncertainties and their evaluation are dis-
the27and28Augustplumestudiescomparedtotheannual cussedextensivelybyRyersonetal.[1998].Examinationof
averages. In the following section, we show that the NO the multiple plume transect data on these 2 days suggests
x
emissions were relatively constant over time and are rea- that the NO mass flux was relatively well conserved over
y
sonably well estimated in the inventory. time. Plume NO /SO ratios remained constant, within
y 2
3.1.3.1. NO Emissions Were Constant Over Time ±30%, between successive transects on these 2 days (e.g.,
x
[27] The NOx emissions information is derived from seeBrocketal.[2003,Figure8]fortheanalysisoftheW.A.
CEMS data for many of the largest NO sources at each Parish plume), suggesting minimal differential loss of NO
x y
complex; these data are believed to be accurate to better relativetoSO and/orCO .Further,thetotalestimatedmass
2 2
than ±30% on average [Placet et al., 2000; Ryerson et al., of NO in each petrochemical plume remained constant
y
1998]. Petrochemical facilities are typically operated con- within±30%overtimedownwindofeachcomplex,inturn
tinuously,sothatvariationintheirNO outputovertimecan suggesting that depositional loss of HNO was relatively
x 3
be minimal (C. Wyman, personal communication, 2001). small compared to the total NO on the timescales consid-
y
As an example, total hourly averaged NO emissions rates ered here. Thus NO appears to have been approximately
x y