ARTICLE pubs.acs.org/est
Long-Term Temporal Variability in Hydrogen Peroxide Concentrations in Wilmington, North Carolina USA Rainwater Katherine M. Mullaugh,*,† Robert J. Kieber,† Joan D. Willey,† and G. Brooks Avery, Jr.† †
Department of Chemistry and Biochemistry, University of North Carolina Wilmington, Wilmington, North Carolina 28403-5932, United States
bS Supporting Information ABSTRACT: Measurements of hydrogen peroxide (H2O2), pH, dissolved organic carbon (DOC), and inorganic anions (chloride, nitrate, and sulfate) in rainwater were conducted on an event basis at a single site in Wilmington, NC for the past decade in a study that included over 600 individual rain events. Annual volume weighted average (VWA) H2O2 concentrations were negatively correlated (p < 0.001) with annual VWA nonseasalt sulfate (NSS) concentrations in low pH ( 5 rains (p > 0.05).
Figure 4A), which is consistent with the known chemistry of the aqueous-phase oxidation of SO2 by H2O2. At higher pH values, O3 is the main oxidant, and no relationship between NSS and H2O2 was observed under these conditions (Figure 4B and Table S2). Implications. The recent decrease of SO2 emissions has removed a major sink for H2O2 in the atmosphere, which may have resulted in the observed increase in H2O2 concentrations in precipitation. The increase in H2O2 driven by lower SO2 emissions has been suggested by other researchers,2 but this is the first data set to provide a lengthy enough sampling campaign to support this hypothesis. H2O2 is one of the most important oxidants in the atmosphere because it is a main source of aqueous phase •OH radicals.5 Changes in the concentration of H2O2 in precipitation presented in this manuscript suggest that there may be a rise of radically mediated transformations potentially altering the overall speciation of organic compounds and trace metals in atmospheric waters. The annual wet deposition of H2O2 in Wilmington, NC calculated from annual VWA H2O2 concentrations (Figure 1A) and local annual precipitation amounts (Figure 1B) is presented in Figure 5. When 2007, the second driest year in the 78-year climatological record in Wilmington, NC, was omitted the increase in wet deposition of hydrogen peroxide between 2001 and 2010 is significant (Mann Kendall trend analysis18 p = 0.024). The average deposition during the preceding 5 years (ca. 27 mmol H2O2 m2 yr1 not including 2007) is more than double the approximately 10 mmol H2O2 m2 yr1 observed in 2001 and 2002. The 20012002 deposition data are near the annual wet deposition of 12 mmol H2O2 m2 yr1 determined at this location between October 1992 and October 1994.27
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Figure 4. (A) Inverse linear correlation between annual VWA concentrations of nonseasalt sulfate (NSS) and H2O2 concentrations for rainwater samples with a pH < 5. The slope of the linear regression is 0.6 NSS/H2O2 (r = 0.871, p < 0.001). The value marked by “X” represents the VWA for data collected at this site from 19921994. These individual events were not sorted according to pH, but approximately 80% of the events over this time period had pH < 5.27 (B) Annual VWA concentrations of nonseasalt sulfate (NSS) and H2O2 concentrations for rainwater samples with a pH > 5 showing no significant correlation.
Figure 5. Annual wet deposition of H2O2 in Wilmington, NC determined from annual volume weighted averages and annual local rainfall amounts.
During this earlier study the VWA H2O2 concentration was 9.6 μM and NSS was 13.7 μM, which are both between the VWA’s for 2001 and 2002 (marked by “X” in Figure 4A). Comparison to the earlier data suggests that the concentrations of H2O2 and NSS at this location did not change in the ten years prior to the temporal trends presented in Figures 1A and 2. We estimate an individual rain event at this location typically deposits 350 μmol H2O2 m2 based on a rain amount of 20 mm 9541
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Environmental Science & Technology (the average rainfall of all the events included in this study) and the VWA H2O2 concentration for 2010 of 17.3 μM. The addition of higher amounts of H2O2 to surface waters via rain is significant given the disparity between typical H2O2 concentrations in rainwater (1100 μM) and surface water (10200 nM). The importance of rainfall to surface water concentrations was demonstrated quantitatively at the Bermuda Atlantic Time Series Station (BATS) during August 1999 and March 2000. Rainwater was responsible for a 2-fold increase in H2O2 concentrations throughout the 25-m mixed layer making wet deposition the dominant source of oceanic H2O2 at this location.28 The increase in wet deposition of H2O2 is particularly significant in the oligotrophic open ocean such as BATS where it has a relatively long half-life of approximately 100 h.8,9 As a labile oxidant, the infusion of excess H2O2 could greatly influence the redox chemistry of surface waters such as altering the speciation or bioavailability of trace metals such as iron and the oxidation state of organic compounds.
’ ASSOCIATED CONTENT
bS
Supporting Information. Figures S1 and S2 and Tables S1S5. This material is available free of charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION Corresponding Author
*E-mail:
[email protected].
’ ACKNOWLEDGMENT Our rainwater research program at UNCW has been continuously supported by a variety of NSF Atmospheric Chemistry grants since 1994 the most recent of which are AGS 0646153 and AGS 1003078. Event-based sampling and timely analysis of rainwater required by this project would not have been possible without the contributions of undergraduate students, master’s students, and postdocs. ’ REFERENCES (1) Gunz, D.; Hoffmann, M. R. Atmospheric chemistry of peroxides: A review. Atmos. Environ. 1990, 24A, 1601–1633. (2) Moller, D. Atmospheric hydrogen peroxide: Evidence for aqueous phase formation from a historic perspective and a one year measurement campaign. Atmos. Environ. 2009, 43, 5293–5936. (3) Kieber, R. J.; Smith, J.; Mullaugh, K. M.; Southwell, M. W.; Avery, G. B.; Willey, J. D. Influence of dissolved organic carbon on photochemically mediated cycling of hydrogen peroxide in rainwater. J. Atmos. Chem. 2009, 64 (23), 149–158. (4) Anastasio, C.; Faust, B. C.; Allen, J. M. Aqueous phase photochemical formation of hydrogen peroxide in authentic cloud waters. J. Geophys. Res. 1994, 99, 8231–8248. (5) Sakugawa, H.; Kaplan, I. R.; Tsai, W.; Cohen, Y. Atmospheric hydrogen peroxide. Environ. Sci. Technol. 1990, 24, 1452–1461. (6) Sander, R. Henry’s Law Constants. http://webbook.nist.gov (accessed June 7, 2001). (7) Calvert, J. G.; Lazarus, A.; Kok, G. L.; Heikes, B. G.; Walega, J. G.; Lind, J.; Cantrell, C. A. Chemical mechanisms of acid generation in the troposphere. Nature 1985, 317, 27–35. (8) Petasne, R. G.; Zika, R. G. Hydrogen peroxide lifetimes in south Florida coastal and offshore waters. Mar. Chem. 1997, 215–225. (9) Cooper, W. J.; Saltzman, E. S.; Zika, R. G. The contribution of rainwater to variability in surface ocean hydrogen peroxide. J. Geophys. Res. 1987, 92, 2970–2980.
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(10) Willey, J. D.; Kieber, R. J.; Avery, G. B. Changing chemical composition of precipitation in Wilmington, North Carolina, USA: Implications for the continental USA. Environ. Sci. Technol. 2006, 40, 5675–5680. (11) Sigg, A.; Neftel, A. Evidence for a 50-percent increase in H2O2 over the past 200 years from a Greenland Ice Core. Nature 1991, 351 (6327), 557–559. (12) Kieber, R. J.; Helz, R. G. Two method verification of hydrogen peroxide determinations in natural waters. Anal. Chem. 1986, 58, 2312– 2315. (13) Willey, J. D.; Kiefer, R. H. A contrast in winter rainwater composition: maritime versus continental rain in eastern North Carolina. Mon. Weather Rev. 1990, 118, 488–494. (14) Jickells, T. D.; Knap, A. H.; Church, T. M. Trace metals in Bermuda rainwater. J. Geophys. Res. 1984, 89, 1423–1428. (15) Khare, P.; Satsangi, G. S.; Kumar, N.; Maharaj, K.; Srivastava, S. S. HCHO, HCOOH, CH3COOH in air and rain water at a rural tropical site in north central India. Atmos. Environ. 1997, 31, 3867–3875. (16) Willey, J. D.; Kieber, R. J.; Eyman, M. S.; Avery, G. B. Rainwater dissolved organic carbon: Concentrations and global flux. Global Biogeochem. Cycles 2000, 14, 139–148. (17) Topol, L. E.; Levon, M.; Flanagan, J.; Schwall, R. J.; Jackson, A. E. Quality assurance management for precipitation systems; EPA/600/ 4-82-042a; Environmental Protection Agency: Research Triangle Park, NC, 1985. (18) Helsel, D. R.; Hirsch, R. M. Statistical Methods in Water Resources, 3rd ed.; Elsevier Science Pub. Co.: 2000. (19) NOAA, Local Climatological Data and Annual Summary with Comparative Data. In National Climatic Data Center: Wilmington, NC, 2010. (20) Wilmington and New Hanover County Planning Department Report; Urban Area Metropolitan Planning Organization: Wilmington, NC, 2009. (21) Lehmann, C. M. B.; Bowersox, V. C.; Larson, S. M. Spatial and temporal trends of precipitation chemistry in the United States, 19852002. Environ. Pollut. 2005, 135 (3), 347–361. (22) van der Swaluw, E.; Asman, W. A. H.; van Jaarsveld, H.; Hoogerbrugge, R. Wet deposition of ammonium, nitrate and sulfate in the Netherlands over the period 19922008. Atmos. Environ. 2011, 45, 3819–3826. (23) Santos, P. S. M.; Otero, M.; Santos, E. B. H.; Duarte, A. C. Chemical composition of rainwater at a coastal town on the southwest of Europe: What changes in 20 years? Sci. Total Environ. 2011, 209 (18), 3548–3553. (24) National Trends in Sulfur Dioxide Levels. http://www.epa. gov/airtrends/sulfur.html (June 7, 2011). (25) National Trends in Nitrogen Dioxide Levels. http://www.epa. gov/airtrends/nitrogen.html (June 8, 2011). (26) Brasseur, G. P.; Orlando, J. J.; Tyndall, G. S. Atmospheric Chemistry and Global Change; Oxford University Press: New York, 1999. (27) Willey, J. D.; Kieber, R. J.; Lancaster, R. Coastal rainwater hydrogen peroxide: Concentration and deposition. J. Atmos. Chem. 1996, 25, 149–165. (28) Kieber, R. J.; Cooper, W. J.; Willey, J. D.; Avery, G. B. Hydrogen peroxide at the Bermuda Atlantic Time Series Station. Part 1: Temporal variability of atmospheric hydrogen peroxide and its influence on seawater concentrations. J. Atmos. Chem. 2001, 39, 1–13.
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