allen

Point source emission variability and its impact on ozone precursor and HAP concentrations in the Houston-Galveston area: 

Point source emission variability and its impact on ozone precursor and HAP concentrations in the Houston-Galveston area David Allen, University of Texas at Austin with contributions by Harvey Jeffries and colleagues at the University of North Carolina

Point source emission variability : 

Point source emission variability Large chemical processing industry (CPI) facilities handle hundreds of millions to billions of pounds per year of material, yet their emission rates for ozone precursors and HAPS are typically in the range of thousands to tens of thousands of pounds per year; emissions are <0.01% of throughput Process upsets can significantly impact temporal patterns of emissions

Point source emission variability: 

Point source emission variability How are point source inventories usually constructed and what role does emission variability play? What is the magnitude and temporal pattern of point source emission variability? What is the effect of this variability on ambient concentrations of ozone precursors and HAPs? Can we model the variability?

How are point source inventories usually constructed and what role does emission variability play?Southeast Texas case study: 

How are point source inventories usually constructed and what role does emission variability play? Southeast Texas case study

Southeast Texas: Reported EI: 

Southeast Texas: Reported EI Normal Non-EGU VOC EI with Special EI additions hg_02km.tx_negu_si4a Total Point Source CB−IV HC Emissions, 08/25/2000 Base inventory of 240 T/D Nearly constant emissions Cantu, 2002

Discrete events in Reported EI: 

Discrete events in Reported EI Additions from the “upset” data hg_02km.tx_negu_up1 Total Point Source CB−IV HC Emissions, 08/29/2000 Less than 1 T/D Cantu, 2002 There was limited reporting of “upsets” in 2000 due to RQ being 5000 lbs above daily permitted values.

Variability in point source emissions: Definitions: 

Variability in point source emissions: Definitions Industrial VOC emissions inventory includes: Permitted emissions Relatively constant sources Fugitives Base load operations (waste water, fired equip., tanks, analyzer vents) Routinely variable Flares Cooling Towers Off-permit event emissions Scheduled Startup, Shutdown, Service events Unscheduled “event” releases.

Point source emission variability: 

Point source emission variability How are point source inventories usually constructed and what role does emission variability play? What is the magnitude and temporal pattern of emission variability? What is the effect of this variability on ambient concentrations of ozone precursors and HAPs? Can we model the variability?

Slide9: 

Focus on both EVENT EMISSIONS and CONTINUOUS EMISSION VARIABILITY

What is an emission event?: 

What is an emission event? Effective September 12, 2002, per Texas Administrative Code (TAC) Title 30 Chapter 101, reportable quantities were reduced from 5000 lbs. to 100 lbs. for most compounds in the Houston/Galveston ozone non-attainment area. Section 101.1, paragraph (83) defines a reportable emissions event as “Any emissions event which, in any 24-hour period, results in an unauthorized emission equal to or in excess of the reportable quantity…”. Alkanes remain at the 5000 lb limit provided they contain less than 0.02% of ethene (ethylene), propene (propylene), butene (butylenes), toluene, acetaldehyde, or oxides of nitrogen, and less than 2.0% of any other reportable compound. In addition, Texas House Bill (HB) 2912 requires that air emission incidents be filed electronically and be available in a publicly available database.

Key Questions regarding emission events: 

Key Questions regarding emission events Are the magnitudes of emission events, singularly and collectively, significant relative to routine emissions? What are the characteristics of the events in terms of time, space, and composition?

Question 1 : Are the magnitudes of these events, singularly and collectively, significant relative to that of routine emissions?: 

Question 1 : Are the magnitudes of these events, singularly and collectively, significant relative to that of routine emissions? Focus on highly reactive volatile organic compounds (HRVOC): ethene, propene, butenes, and 1,3-butadiene Emissions are evaluated in terms of flow (lbs/hr) TCEQ Air Emission Event Report Database is used as source of data

Slide13: 

First 11 Months of reporting: NOx emission event emissions are small compared to annual average emissions At specific times and locations, VOC and HRVOC emissions can be large relative to annual average emissions Average hourly emissions of all point sources, 2001 inventory

Slide14: 

Total mass of over 4 millions pounds (2000 tons) contributes 4% to the 45,000 tons of VOC emitted over a single year from point sources in the four counties. 14 times (18 hours) during the eleven-month period, event emissions exceed the annual average for all facilities in the region. 4 times in 11 months, the flow rate of event emissions is more than five times the annual average with a maximum of 86,000 lbs/hr. VOCs 4,000,000 lb

Slide15: 

Total mass of over 1.6 millions pounds (830 tons) is ~12% of the 6800 tons of HRVOC emitted over a single year from point sources in the four counties. 29 times (115 hours) during the eleven-month period, event emissions exceed the annual average. 7 times in 11 months, the flow rate of event emissions is more than five times the annual average with a maximum of 39,000 lbs/hr. HRVOCs 1,650,000 lb

Slide16: 

1,3-Butadiene ~50,000 lb Butenes ~100,000 lb Propene ~500,000 lb Ethene ~1,000,000 lb

What are the characteristics of the events in terms of time, space, and composition? : 

What are the characteristics of the events in terms of time, space, and composition? Most HRVOC events last less than a day, many last less than an hour Largest number of events is from events of 100-1000 lb, but most of the mass is associated with events greater than 1000 lb, which occur, on average, several times per week 2-3 times per week Daily Less than 24 hours

Conceptual model: 

Conceptual model Events with HRVOC emissions of more than 100 lb/hr occur daily, on average Events with HRVOC emissions of more than 1000 lb/hr occur several times per week, on average Events with HRVOC emissions of more than 10,000 lb/hr occur several times per month, on average Many are relatively short (well under one hour in duration) Among the HRVOCs, ethene and propene dominate the mass of emissions Events occur primarily in Harris and Brazoria counties at chemical manufacturing facilities

Point source emission variability: 

Point source emission variability How are point source inventories usually constructed and what role does emission variability play? What is the magnitude and temporal pattern of emission variability? What is the effect of this variability on ambient concentrations of ozone precursors and HAPs? Can we model the variability?

Variability in ambient concentrations in industrial source regions : 

Variability in ambient concentrations in industrial source regions Spatially dense monitors in industrial source region – primarily auto-GC Focus on Seabrook monitor – FTIR FTIR monitor has 15 minute time resolution but higher detection limits http://raqis.radian.com/pls/raqis/friendshippark

Ambient concentration variability of ozone precursors and HAPs: 

Ambient concentration variability of ozone precursors and HAPs

Ambient concentration variability of ozone precursors and HAPs: 

Ambient concentration variability of ozone precursors and HAPs

Ambient concentration variability of ozone precursors and HAPs: 

Ambient concentration variability of ozone precursors and HAPs

Ambient concentration variability of ozone precursors and HAPs: 

Ambient concentration variability of ozone precursors and HAPs Meteorological variability can also contribute to concentration variability, but: Event emission reporting provides evidence for temporal variability in emissions A variety of aircraft and ground based observational data indicate that meteorology cannot account for all of the emission variability

Point source emission variability: 

Point source emission variability How are point source inventories usually constructed and what role does emission variability play? What is the magnitude and temporal pattern of emission variability? What is the effect of this variability on ambient concentrations of ozone precursors and HAPs? Can we model the variability?

Can we model the emission variability? Event emissions: 

Can we model the emission variability? Event emissions Stochastic modeling of emission events uses probability distribution function, based on hourly emission rates

Other sources of emission variability: Discrete events that are not reported in event data base and variability in continuous emissions: 

Other sources of emission variability: Discrete events that are not reported in event data base and variability in continuous emissions

Estimating variability for continuous emissions: 

Estimating variability for continuous emissions Collect data on a sample of unit operations Assign variability in emissions (as a percentage of annual flow) to all “similar” point sources Calculate emission snapshots

Estimating variability for continuous emissions: 

Estimating variability for continuous emissions As domain size decreases, magnitude of variability (as a percentage of annual flow) increases Variability increases as specific compounds, as opposed to all VOCs, are examined.

Can we model the concentration variability?: 

Can we model the concentration variability? Focus has been on modeling ozone precursors in an eulerian photochemical model CAMx able to generally replicate high concentrations and rapid ozone and formaldehyde production observed by aircraft but simulations must be done at 1 km grid resolution

Point source emission variability: 

Point source emission variability How are point source inventories usually constructed and what role does emission variability play? Constant emissions, 24/7, does not capture extremes in concentration What is the magnitude and temporal pattern of emission variability? Short duration (<1 hr) emissions dominate variability; events occur daily in Houston What is the effect of this variability on ambient concentrations of ozone precursors and HAPs? Events can cause acute exposures Can we model the variability? Tools are emerging for modeling both emissions and concentrations