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Analysis of Fine and Coarse Nitrate at Thompson Farm

Analysis of Fine and Coarse Nitrate at Thompson Farm. By Brian Cook. Motivation. Determination of the fractions of aerosol nitrate in the fine and coarse modes Further, to determine the fraction of the coarse nitrate that is associated with sea salt particles as opposed to dust particles

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Analysis of Fine and Coarse Nitrate at Thompson Farm

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  1. Analysis of Fine and Coarse Nitrate at Thompson Farm By Brian Cook

  2. Motivation • Determination of the fractions of aerosol nitrate in the fine and coarse modes • Further, to determine the fraction of the coarse nitrate that is associated with sea salt particles as opposed to dust particles • We care what fraction of nitrate is in fine particles because these have a more pronounced health effect, and they have a greater effect on climate. • These fractions must be determined by calculation as only bulk nitrate is measured at Thompson Farm. Size distribution data are unavailable.

  3. Nitrate Formation • Fine Nitrate Formation: • NH3+ H2SO4 NH4HSO4 • NH4HSO4 + NH3 (NH4)2SO4 • When there is excess ammonia, • NH3 + HNO3 NH4NO3 • Coarse Nitrate Formation: • HNO3 + NaCl NaNO3 + HCl • 2HNO3 + CaCO3 Ca(NO3)2 + H2CO3 • Sulfuric acid can act as nitric acid in these reactions, though to a much smaller degree

  4. Calculating Fine and Coarse Nitrate • If excess ammonia exists, ( NH4+ > (x)(SO42-) ) • Where x = 1 for pure ammonium bisulfate (NH4HSO4) and 2 for pure ammonium sulfate ( (NH4)2SO4 ) or some number between if there is a mixture. • Then, NO3- (fine) = NH4+ - (x)(SO42-) (excess NH4+) • NO3- (coarse) = NO3- – NO3- (fine) • When NH4+ < (x)(SO42-) • All ammonium is tied up with sulfate, so no fine nitrate can form. All detected nitrate must be coarse nitrate associated with sea salts and dust.

  5. Continental Source Regions Continental Canada N=291 Continental Midwest N=50 Continental Coast N=98

  6. Marine Source Regions Marine Marine Canada N=13 N=70 Marine Coast N=73

  7. Cl D E P L E T I O N (PPTV) Continental Con Con Marine Marine Marine Canada Coast Midwest Canada Coast Chloride Depletion by Source Region

  8. nss-Ca2+ and Mg2+ by Source Region Mg2+ (eq) nss-Ca2+ (eq) C/Canada C/Coast C/Midwest Marine M/Canada M/Coast C/Canada C/Coast C/Midwest Marine M/Canada M/Coast

  9. NH4+and nss-SO42- by Source Region nss-SO42- (PPTV) NH4+ (PPTV) C/Canada C/Coast C/Midwest Marine M/Canada M/Coast C/Canada C/Coast C/Midwest Marine M/Canada M/Coast

  10. Total Nitrate NO3- (PPTV) Continental Con Con Marine Marine Marine Canada Coast Midwest Canada Coast

  11. NH4+ / SO42- Ratios • If NH4+ > (x)(SO42-) then NO3- (fine) = NH4+ – (x)(SO42-) • Otherwise, NO3- (fine) = 0 MEAN FINE NITRATE (PPTV)

  12. Fine Nitrate Analysis X=2.0 Fine NO3- (PPTV) C/Canada C/Coast C/Midwest Marine M/Canada M/Coast

  13. Coarse Nitrate vs. Mg2+ NO3– (coarse) vs. Mg2+ NO3– (eq) Mg2+ (eq)

  14. Coarse Nitrate vs. Ca2+ NO3- (coarse) vs. Ca2+ NO3– (eq) Ca2+ (eq)

  15. CONCLUSIONS • Most chloride depletion comes from polluted coastal regions (high Cl and pollution) • The Continental/Midwest and Canada regions have the highest fractions of fine nitrate because they have high ammonium relative to sulfate (farming) • We get Coarse nitrate from both sea salts and dust particles at Thompson Farm. But, we are unable to determine the exact fractions of each without more data.

  16. Acknowledgments • Rob Griffin • Carolyn Jordan • George Hurtt • Research and Discover Program

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