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Primary and Secondary (Gaseous Precursor) Emissions of PM 2.5. Number of samples: Fort Benning Flaming (5), Smoldering (5), Fort Gordon Flaming (4), Smoldering (3), Background (19).

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Primary and Secondary (Gaseous Precursor) Emissions of PM2.5

Number of samples:

Fort Benning Flaming (5), Smoldering (5),

Fort Gordon Flaming (4), Smoldering (3),

Background (19)

According to EPA’s emission inventory [1999] 18 % of primary PM2.5 emissions come from forest fires (wildfire and prescribed fire), 11.4 % and 5 %, for CO and Volatile Organic Compounds (VOC), respectively. Forest fire is a significant source of gaseous and particulate air pollutants, which are not well characterized in terms of their chemical composition and atmospheric reactivity. Some of the gaseous emissions are believed to be more reactive and act as precursors for secondary fine PM formation during atmospheric dispersion of the smoke plume. Secondary organic aerosol (SOA):

Organic compounds, some highly oxygenated, residing in the aerosol phase as a function of atmospheric gas or particle phase reactions.

SOA formation mainly depends on:

Emissions & forming potential of precursors

aromatics (BTX, aldehydes, carbonyls)

terpenes (mono-, sesqui-)

other biogenics (aldehydes, alcohols)

Presence of other initiating reactants

O3, OH, NO3, sunlight, acid catalysts

Mechanisms (with half hr to few hr yields):

Gas-to-particle conversion/partitioning

e.g. terpene oxidation

Heterogeneous reactions

aldehydes via hydration and polymerization, forming hemiacetal/acetal with alcohols

Particle-phase reactions

H2SO4-accelerated acetal formation

[Jang and Kamens, ES&T 2001]

Links to O3 Photochemistry:

Same precursors that form O3 play also a critical role in SOA formation. The determination of SOA contribution to total ambient PM2.5 mass observed at any receptor site is very difficult due to the above complex interactions, and can only be estimated from indirect methods. Due to the significant emissions of primary PM, however, EPA’s air quality regulations mandated by the Clean Air Act require the attainment of annual NAAQS for PM2.5, whereas O3 needs to be regulated only during the summer months.

O3

SOA

CO

CO2

VOC

NOx

PM

Toxics

5-year Average Monthly Totals of Prescribed Burns in GA

CE (%)

VOC canister sampling

  • VOC Source Apportionment at OLC Receptor Site
  • The Chemical Mass Balance (CMB) vers. 8 was used applying source profiles from Photochemical Assessment Monitoring Stations (PAMS) in the U.S. [Watson et al. 1998]. The CMB model worked well under the following assumptions:
  • compositions of source emissions are constant over the sampling periods;
  • chemical species do not react with each other;
  • all potentially contributing sources were identified and their emissions characterized;
  • the number of source categories is less than or equal that of chemical species;
  • the source profiles are linearly independent of each other; and
  • measurement uncertainties are random, uncorrelated, and normally distributed.
  • Findings:
  • Contributions from 7 source categories to total 28 measured VOC identified.
  • Significant Prescribed Burning contributions only at night and early morning.
  • Importance of continued smoldering emissions into shallow nighttime BL.
  • Biogenic contributions highest at midday, significant only in warmer season.

Scale!

Fall-Line

Photochemical processes leading to SOA linked to O3 formation, hence SOA must be expected higher in summer than in winter.

  • Indications for SOA
  • 1) PM2.5 Seasonal Differences
  • in Air Mass Transport
  • Ambient air quality measurements were made during the Atlanta Supersite Experiment in August 1999 [Baumann et al. JGR 2003, Solomon et al. JGR 2003], and within the Fall-line Air Quality Study (FAQS) at Griffin, Macon, Columbus and Augusta from summer 2000 to fall 2003. PB emission measurements were conducted at Fort Benning, SE of Columbus, and at Fort Gordon, S of Augusta, in winter/spring 2003 and April 2004.
  • The PM2.5 summer/winter wind roses show
  • Higher [PM2.5] in summer region-wide;
  • Atlanta being a major source for PM2.5;
  • potentially impacting Fall-line cities

with SOA formed during transport;

  • more local impacts (from PB) in winter.

Decreasing Occurrence and Size of Wild Fires With Increasing Prescribed Burns on Fort Benning, GA

Case Study of Local PM2.5 Exceedance

Annual NAAQS

24h NAAQS

2) PM2.5 Seasonal Differences in Diurnal Variability

Metro Atlanta

Macon

Columbus

Augusta

Coastal Sites

Annual NAAQS

Comparison of measured (OLC) and predicted (GFC) wind data (top), boundary layer mixing height (BLH) and atmospheric stability indicators (center, with daily T max/min difference), areas of prescribed burns and wild fires incl. their directions and distances from OLC with 24 h average [PM2.5] from OLC, Griffin, Macon, and Augusta (bottom), for 5 weeks in fall 2001. The blue open circles and triangles are the state’s regulatory FRM data from Columbus’ Cusseta Rd. (5 km N of OLC) and the Health Dept. (11 km N of OLC), respectively, both missing the exceedances of the continuous OLC measurements due to their 1/3 schedule.

Correlation of 24 h [PM2.5] at OLC with total acres burnt, considering the fire location (distance and direction) relative to OLC, and the projected plume trajectory as a measure for potential plume impact (largest if equal 1, placing OLC directly downwind), with the lower atmosphere stability indicator (Tmax - Tmin), wind speed (top), and with the GFC model predicted BLH for the day the burn or wild fire occurred as well as for the succeeding night (bottom). The date labels in the legend (right) point to a continued accumulation of fine PM pollution and contribution from smoldering fires until several days after the actual flaming stage.

Regional Non-attainment of the Annual NAAQS for PM2.5 During Dry Years

OM/OC 1.9 1.5 2.2 1.6 1.9 2.1 2.0

OC/EC 15 19 8 19 26 26 26

Acres burnt 0 937 1256 3770 4006 504 251

Midday minimum due to BL mixing in winter (right) seems compensated by SOA in summer (left);Similar bimodal variability at all sites except for summer 2000 (incomplete data);PM2.5 sources near Columbus drive nighttime averages in winter 2001/02;Standard deviations of those indicate rare occurrences of extreme values;Summer stagnation with high O3 also leads to high PM2.5 (e.g. 2000);Annual PM2.5 NAAQS (15 mg m-3) sensitive to:- SOA formed under regional stagnation in summer;- Primary PM2.5 from local sources at night in winter.

Prescribed Burning and the Development of a Smoke Management Plan (SMP) in Georgia

Karsten Baumann1, Sangil Lee2, Mark Clements3, Polly Gustafson4

1School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA

2School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA

3Southeast Regional Office, Installation Management Agency, U.S. Army, Fort McPherson, GA

4Environmental Management Divisio0n, U.S. Army Infantry Center, Fort Benning, GA

Prescribed Burning Activities in GA

Prescribed burning (PB) is a common land management practice in GA with 24.4 million acres of forested land. Of the 17.6 million acres privately owned forests alone, more than 1 million acres are burnt annually. Most forested areas are burnt in winter and spring. Agricultural burns gain importance in summer. Highest burn intensities occur on military installations where up to 5,000 acres can be burnt on a single day. The three largest military installations are Forts Stewart, Benning, and Gordon, which burn ~50,000, 30,000 and 12,000 acres every year, respectively. Here, PB emissions were determined at three different locations and evaluated in the context of long-term air quality measurements and the development of a Smoke Management Plan (SMP) for GA.

VOC Profile of Emissions from Flaming and Smoldering

Combustion efficiency (CE)

clearly different:

Flaming = 91-92 % vs.

Smolder = 81-82 %

ΔC: excess C concentration

[Ward and Hao, 1992]

  • VOC concentrations are orders of 10 to 1000 higher near the source.
  • VOC are generally higher during flaming than smoldering but similar in profile.
  • Emissions of certain alkenes, aromatics and biogenics are higher than others.
  • These are particularly efficient precursors for atmospheric O3 and SOA formation.
  • Average VOC profile valid for characterizing prescribed burning (PB) source.
  • New PB source profile suitable for VOC source apportionment at receptor sites.

See below…

Benefits

Georgia’s economy is heavily supported by agriculture and forestry. Both vocations utilize prescribed burning practices to cultivate agriculture and maintain healthy forests. The State of Georgia regulates open burning to assure air quality, minimize fire danger and protect wildlife species such as bob-white quail, eastern wild turkey, white-tail deer, and red-cockaded woodpecker that are protected by the Endangered Species Act (ESA) or designated by state initiatives for wildlife management. Many native songbirds and plants also depend on a natural fire ecology. Fort Benning fire statistics also show that prescribed burning reduces the occurrence and size of unwanted wild fires, and ultimately protects human lives and property. Prescribed Burning is therefore considered in the U.S. government’s Healthy Forests Restoration Act as an important measure to reduce fuel loads and the risk of catastrophic wild fires across the Nation.

SOA

The Conflict With Air Quality

The general trend in annual [PM2.5] at the State’s regulatory monitoring network is a uniform decrease across all 26 sites since 1999. This trend seems climatologically driven by precipitation, the main sink for atmospheric PM. The annual state-wide totals for the years 1999 thru 2003 were 40.9, 41.7, 42.9, 50.3, and 58.2 inches, compared to a 30-year normal (1961-1990) of 50.8 inches. All sites outside metro Atlanta benefited from the last two wet years and attained the annual NAAQS of 15 mg m-3. While the metro Atlanta sites experience the highest concentrations, the coastal sites remain the cleanest, apparently benefiting from diluting effects associated with the land-sea breeze circulation.

PM2.5 Mass and Composition at OLC near Fort Benning in 2003

“Others” includes K+, Na+, Cl-, and “LOA” includes acetate, formate and oxalate. Acres burnt are prescribed burns conducted on the Fort during each given period. The OM/OC ratios derived from mass closure provide some measure of the degree of POC oxygenation showing a trend toward higher values later in the season. The less uncertain OC/EC indicates relative change in SOA contribution, which was low early in the season, when photo-chemical activity was low (see max-O3). More SOA from regional sources in aged air masses contributed to total POM at the end, while more primary OPOC contributed earlier in the season.

Conclusions and Outlook

  • Most monitoring sites in GA exceed the annual NAAQS for PM2.5, coastal sites benefit from land-sea breeze circulation.
  • Regional trend in decreasing PM2.5 levels correlates with increasing annual total precipitation state-wide.
  • SOA is indicated indirectly to contribute significantly to observed ambient PM2.5 levels in summer months regionally.
  • SOA seems to compensate deeper BL mixing height in summer by secondary formation during atmospheric transport.
  • PM2.5 mass and its organics fraction increase with increasing atmospheric photochemical activity indicated by O3.
  • Prescribed burning (PB) emissions contain high levels of VOC precursors with substantial potential for SOA formation.
  • PB emissions influence the local PM2.5 mass and its organics fraction measured at OLC near Fort Benning.
  • The PB influence on PM2,5 mass is highest at night and early mornings, reaching extreme values during Oct-Nov 2001.
  • Exclusion of the five exceedance days would yield attainment of the annual NAAQS for PM2.5 in 2001.
  • Stable nocturnal stratification identified indirectly by max/min T difference and wind speed influence PM2.5 levels most.
  • Continued emissions from smoldering fires accumulate in shallow nocturnal BL layers and burden local air quality.
  • Forecasting of nocturnal BL height difficult due to complex, detailed land coverage and topography features.
  • PCA will be applied to a statistically robust, extended data set to determine the most important forecast parameter.

Acknowledgement

Part of this work was funded by the EPA/DOD Region 4 Pollution Prevention Partnership Small Grants Program and the U.S. Army Corps of Engineers via Engineering & Environment, Inc. subcontract NC03-05SUB01. The FAQS is directed by Dr. Michael Chang from EAS at Georgia Tech. OLC members from Columbus State University and LMB Personnel from Forts Benning and Gordon assisted with the VOC sampling and provided burn data. The VOC analysis was performed by Dr. Don Blake at UC Irvine. Daniel Chan from the Georgia Forestry Commission (GFC) provided state-wide burn data and forecast products.