Uncertainties in isoprene-no x -O 3 chemistry: Implications for surface ozone over the eastern United States PAR TEMP

Size: px

Start display at page:

Download "Uncertainties in isoprene-no x -O 3 chemistry: Implications for surface ozone over the eastern United States PAR TEMP"

Joleen Skinner
5 years ago
Views:

States ISOPRENE + NO x O 3 PAR TEMP Leaf Area Arlene M.

1 Uncertainties in isoprene-no x -O 3 chemistry: Implications for surface ozone over the eastern United States ISOPRENE + NO x O 3 PAR TEMP Leaf Area Arlene M. Fiore Telluride Atmospheric Chemistry Workshop August 11, 2004

Recent Changes in Biogenic VOC Emissions based upon analysis of > 280,000 forest plots substantial isoprene increases in southeastern USA largely driven by human land-use decisions Isoprene

2 Recent Changes in Biogenic VOC Emissions based upon analysis of > 280,000 forest plots substantial isoprene increases in southeastern USA largely driven by human land-use decisions Isoprene [Purves et al., Global Change Biology, 2004] Monoterpenes Sweetgum Invasion of Pine plantations Percent Change mid-1980s to mid-1990s Trends in anthropogenic precursors?

html) CO VOC NO x -20 10 0 +10 +20 +30 Percent Change Large decreases in

3 Trends in Anthropogenic Emissions: 1985 to 1995 from US EPA national emissions inventory database ( CO VOC NO x Percent Change Large decreases in CO and VOC Emissions Some local increases in NO x Higher biogenic VOCs Net effect On O 3?

4 Tool: GEOS-CHEM tropospheric chemistry model [Bey et al., 2001] Uses assimilated meteorology: GEOS-3 1 x1 fields for vertical levels ( 9 below 2 km) Regridded to 4 x5 for global spinup and boundary conditions for nested 1 x1 resolution over North America [Wang et al., 2004; Li et al., 2004] 31 tracers; NO x -CO-hydrocarbon-O 3 chemistry coupled to aerosols GEIA isoprene inventory [Guenther et al., 1995] v ( July p.m. Surface O 3 (ppbv)

5 Model Evaluation: July p.m. Surface O 3 (ppbv) Mean Bias = 6±7 ppbv r 2 = 0.4

, 2004] Low-NO x regime? e.g. titration of OH in pre-industrial [Mickley et al.

6 Isoprene increases reduce O 3 in Southeastern US Standard GEOS-CHEM 1x1 N. American Nested simulation: July 1-5 p.m. O 3 Change in July 1-5 p.m. surface O 3 (ppbv) + Isoprene emission changes from mid-80s to mid-90s [Purves et al., 2004] Low-NO x regime? e.g. titration of OH in pre-industrial [Mickley et al., 2001] & tropical [von Kuhlmann et al., 2004] boundary layers (%)

mean Ozone NO x - saturated High-NO x NO x- sensitive Low-NO x NO x isoprene-saturated?

7 Increasing Isoprene Decreases Ozone in Low-NO x environment GEOS-CHEM base-case July 1-5 p.m. mean Ozone NO x - saturated High-NO x NO x- sensitive Low-NO x NO x isoprene-saturated?? VOC SE US is near maximum VOC capacity point, beyond which VOCs suppress O 3 formation; [Kang et al., 2003]. ISOP Isoprene-saturated GEIA simulation: biogenics+o 3 (10d) comparable to O 3 +HO x (16d), hν -> OH (11d) in SE US (31-37N; 81-91W)

8 Isoprene can decrease surface O 3 by: (1) Sequestering NO x as organic isoprene nitrates (2) Titrating OH and enabling direct reaction of isoprene with O 3 High-NO x (very fast) OH Isoprene O 3 (slower ) RO 2 O 3 NO NO 2 O 3 Isoprene nitrates HO 2 ROOH OH Low-NO x, high-isoprene Uncertainties in the fate of organic nitrates and peroxides: Sinks of HO x / NO x vs. recycling of radicals?

9 Impact on surface O 3 from uncertainties in chemical fate of organic isoprene nitrates & peroxides Change in July mean 1-5 p.m. surface O 3 (MOZART-2) When isoprene nitrates act as a NO x sink When organic peroxides act as a HO x sink

Choice of isoprene emissions critical for predicting

molec cm -2 s -1 ) 0.47 TgN Difference in July 1-5 p.m. surface O 3 (Purves GEIA) GEIA 3.

10 Choice of isoprene emissions critical for predicting surface O 3 GEIA: global inventory Anthrop. NO x emissions 5.8 TgC Purves et al., [2004] (based on FIA data; similar to BEIS-2) (10 11 molec cm -2 s -1 ) 0.47 TgN Difference in July 1-5 p.m. surface O 3 (Purves GEIA) GEIA 3.0 TgC (10 11 molecules isoprene cm -2 s -1 ) (ppbv)

) Isoprene reduced 25% NO x reduced 25% With GEIA July Anthropogenic NO x

11 Surface Ozone Response to isoprene and anthropogenic NO x emissions: sensitive to isoprene inventory choice Change in July O 3 (ppbv; 1-5 p.m.) Isoprene reduced 25% NO x reduced 25% With GEIA July Anthropogenic NO x Emissions With Purves (10 11 molec cm -2 s -1 ) High-NO x : O 3 as isop Low-NO x, high isop: O 3 as isop

NO x emissions (ppbv) (ppbv) (ppbv) With Purves With GEIA (ppbv)

12 PAN most influenced by isoprene in high-no x locations Mean July at surface Change from -25% isoprene emissions Change from -25% anthrop. NO x emissions (ppbv) (ppbv) (ppbv) With Purves With GEIA (ppbv) (ppbv) (ppbv) Little effect on PAN in SE US where isoprene changed most

. Changes With Anthro.+ BVOC Changes With Purves et al.

13 Change in Mean July Surface O 3 (ppbv; 1-5 p.m.) reflecting 1980s to 1990s emissions changes With BVOC Changes With Anthrop. Changes With Anthro.+ BVOC Changes With Purves et al. Isoprene Emis With GEIA Isoprene Emis Changes in Anthropogenic NO x emissions dominate O 3 response But response depends upon choice of isoprene emission inventory Comparison with observed changes? Impact on high-o 3 events?

14 Model vs. Obs.: Change in July O s to 1990s (ppbv; 1-5 p.m.) Obs: EPA AIRS GEOS-CHEM: GEIA GEOS-CHEM: Purves ( ) ( ) Poor correlation (r 2 ~ 0) between observed and simulated changes Observed changes in O 3 are not explained by emission changes alone

15 Northeast Southeast GEIA Impact of Sensitivity Simulations on High-O 3 Events: Purves decrease with isoprene except for GEIA SE decrease with NO x, larger response with GEIA dominated by anthrop. (NO x ) emissions changes from 1980s to 1990s but BVOC changes may offset (Purves case) decreases of most extreme events

16 Preliminary Conclusions & Remaining Challenges Better constrained isoprene emissions are needed to predict O 3 response to both anthrop. and biogenic emission changes Utility of satellite CH 2 O columns? New inventories (MEGAN, BEIS-3) more accurate? NASA INTEX-NA observations?

17 Isoprene emissions July 1996 GEIA BEIS2 7.1 Tg C 2.6 Tg C MEGAN GOME 3.6 Tg C 5.7 Tg C [10 12 atom C cm -2 s -1 ] [from Paul Palmer]

18 Vertical slices through 34N: enhanced isoprene, CH 2 O, PAN at surface & upper trop for GEIA compared to Purves With PURVES Altitude With GEIA Longitude Insights from NASA INTEX-NA flights over SE US?

19 Preliminary Conclusions & Remaining Challenges Better constrained isoprene emissions are needed to predict O 3 response to both anthrop. and biogenic emission changes Utility of satellite CH 2 O columns? New inventories (MEGAN, BEIS-3, GLOBEIS) more accurate? NASA INTEX-NA observations? Recent isoprene increases may have reduced surface O 3 in the SE Does this regime actually exist? Can chemical indicators help? Fate of organic nitrates produced during isoprene oxidation?

20 Chemical indicators for O 3 or as Isoprene Isoprene OH RO 2 NO NO 2 O 3 High-NO x Isoprene nitrates HO 2 ROOH OH Change in O 3 for 25% decrease in isoprene emissions HO 2 /NO H 2 O 2 /HNO 3 Potential for using observations to diagnose isoprene-saturated regime, as for NO x -sensitive vs. NO x -saturated [e.g. Sillman, 1995]

21 Preliminary Conclusions & Remaining Challenges Better constrained isoprene emissions are needed to predict O 3 response to both anthrop. and biogenic emission changes Utility of satellite CH 2 O columns? New inventories (MEGAN, BEIS-3, GLOBEIS) more accurate? NASA INTEX-NA observations? Recent isoprene increases may have reduced surface O 3 in the SE Does this regime actually exist? Can chemical indicators help? Fate of organic nitrates produced during isoprene oxidation? Reported emission changes from 1980s to 1990s alone do not explain observed O 3 trends Role of decadal shifts in meteorology? Are anthropogenic emissions inventories sufficient to support trend studies? (Parrish et al., JGR 2002: inconsistencies with CO:NO x ratios from road traffic in EPA inventories vs. ambient msmts)

22 Acknowledgments Larry Horowitz Chip Levy Drew Purves Steve Pacala Mat Evans Qinbin Li Bob Yantosca Yuxuan Wang

Recent Changes in Eastern U.S. Forests: Implications for Air Quality

Recent Changes in Eastern U.S. Forests: Implications for Air Quality Arlene M. Fiore Seminar at the Center for Sustainability and the Global Environment (SAGE) University of Wisconsin-Madison December