Tropospheric Chemistry Overview (or, 40 years in 20 minutes)

1. Tropospheric Chemistry Overview(or, 40 years in 20 minutes) Jennifer A. Logan Recent Results in Planetary Sciences, Atmospheric Chemistry, Climate and Energy Policy A symposium in celebration of Michael McElroy's contributions March 20, 2010.

2. 1949 1970 1980 1990 2000 2010 A short history of tropospheric chemistry highlighting MBM’s contributions • 1949: Migeotte - identifies CO in the atmosphere in solar absorption, ~100 ppb • 1969: Weinstock – shows lifetime of CO is ~1 month, based on 14CO and its budget, and suggests removal by OH • 1971: Levy - first model of tropospheric OH, ~3x106 molec/cm3 at noon; CO lifetime is ~2 months, and CH4 oxidation is a source of HCHO (15 reactions) • 1971, 1972:McConnell, McElroy, and Wofsy - show that CH4 oxidation is a large source of CO (also suggest sources from terpenes) (1-d model, 32 rxns) • Also show that CH4 oxidation is a source of H2O in the stratosphere • 1973: Chameides and Walker, Crutzen - first models of tropospheric ozone

3. 1970 1980 1990 2000 2010 Science, Levy Nature, McConnell et al. CH4 data used to test model

4. 1970 1980 1990 2000 2010 1975 • Mid-late 1970’s – the stratosphere and Mars • 1975: Two postdocs join MBM’s group

5. 1970 1980 1990 2000 2010 • 1981: Logan, Prather, Wofsy and McElroy - global model of trop. chemistry, constrained by observations of O3, CO, CH4, HNO3, H2O (51 rxns) • inventory for all sources of CO (P=2740 Tg) • remote sources of NOx are ~10 Tg, based on almost no data • used CH3CCl3 (MCF)and a box model to test OH • used OH to infer global budget for CH4 (580 Tg) and other gases • trop. ozone budget, P=3840 Tg, L=2820 Tg • All within ~20% of present day values

6. 1970 1980 1990 2000 2010 NOx observations and model (lines) OH, HO2 vs. NO CO observations

7. 1970 1980 1990 2000 2010 Atmospheric Chemistry within a General Circulation Model • 1978-1980: Mahlman & Moxim, Levy et al. - first tracer model of ozone using archived GCM fields, no chemistry • 1981: McElroy and Wofsypropose to NASA to develop “a global 3-D model with realistic dynamics and chemistry”, using the GCM developed by Jim Hansen et al. at GISS, building on their tracer model (Section 4 of a 103 page proposal!) Issues identified include • an accurate method for transport • tracer conservation • efficient techniques for chemical rates • use of activity data for anthropogenic emissions

8. 1970 1980 1990 2000 2010 Strategy outlined in the 1981 proposal Elucidate transport mechanisms, and include a strategy for model validation using observations • Use CFCs to test interhemispheric transport • Simple chemistry • Requires strict numerical accuracy • Use radioactive tracers to test downward transport from the stratosphere, including 7Be • Global model for OH – test with MCF • Use observed distributions of CH4, CO, O3, NOx, and H2O • Compute the time evolution of MCF • Global model for CO with sources prescribed • Tropospheric ozone as an active tracer

9. The holy grail – tropospheric ozone “A reliable description of ozone presumes a model for NOx, for CO, for H2O, for OH and for heterogeneous chemistry, in addition to a satisfactory representation of the stratosphere and a valid description of troposphere-stratosphere exchange. It is unlikely that we can complete work on such a model within three years, but we expect to make substantial progress.” MBM, 1981.

10. 1970 1980 1990 2000 2010 1985: Another new post-doc Major steps in development of the chemical tracer model (CTM) • 1986: Prather – 2nd order moments scheme for accurate non-diffusive 3-d advection • 1987: Prather et al. – CFCs as Tracers of Air Motion • development of the CTM, many technical issues described • sub-grid diffusion needed for correct interhemispheric gradient Wet and dry convection Higher resolution window

11. 1970 1980 1990 2000 2010 • 1990: Spivakovsky, Wofsy and Prather – chemistry parameterization for computation of OH • 1990: Spivakovsky et al. Tropospheric OH in a 3-d CTM – an assessment based on MCF • used observations of CO, CH4, O3, NOt, and column O3 • MCF lifetime with model OH is 5.5 y, MCF data implies 6.2 y • OH fields provided to the community Updated and extended in Spivakovsky et al. (2000) • 1990: Jacob and Prather – 222Rn as a test of convective transport in a GCM

12. 1970 1980 1990 2000 2010 And finally, ozone, 12 years after the original proposal • 1993: Jacob et al. – summertime ozone over the US • used 6 tracers, parameterized chemistry • sub-grid power-plant and urban plumes (Sillman et al., 1990) • observations for boundary conditions • gridded emissions from EPA, isoprene emissions • dry deposition, wet deposition (Balkanski et al. 1993) • evaluated with observations

13. 1970 1980 1990 2000 2010 And 17 years after MBM’s proposal – global ozone • 1998: Wang, Jacob, and Logan – 3 papers on global model of O3-NOx-hydrocarbons • 15 chemical tracers, new parameterizations • global emission inventories from fossil fuel/industry • biomass burning inventory, biogenic emissions • lightning NOx • stratospheric ozone flux • extensive evaluation with observations All of the above work used the GISS GCM fields • 2001: Bey et al. – Global tropospheric chemistry with assimilated meteorology – GEOS-Chem model • GEOS met. fields from NASA • Gear solver for chemistry (in window model earlier) • Adopted many features from GCM based CTM

14. 1970 1980 1990 2000 2010 Déjà vu: from a “window” in 1987 to a nested grid formulation • 2004: Yuxuan Wang, McElroy et al. – nested grid model for Asia. Aircraft observations downwind of Asia in 2001 1° x 1° resolution CO data model,1° x 1° Model, 4° x 5° Applications to CO, NOx, ozone –tomorrow, China Project talks.

15. Data Methane hindcast with a CTM, 1987-1998 • 2004:J. Wang, Logan, McElroy et al. – causes of the slowdown and variability in the CH4 growth rate CH4 growth rate, ppb/yr • Slowdown in growth rate: • slower growth in sources - the economic downturn in the former Eastern bloc • increases in OH - column ozone decr. (solar cycle + trends) • Variability • wetland emissions + OH (especially post-Pinatubo) • Results also showed model OH is too high (Wang et al., 2008)

16. 1970 1980 1990 2000 2010 Satellites Aircraft, ships, sondes, lidars Tropospheric chemistry in the 21st century Satellites provide a global continuous mapping of atmospheric composition, augmenting the otherwise sparse observing system The NASA “A-Train” Models Surface sites D.J. Jacob Terra – CO data since 2000; Aura – CO, O3, NO2, HCHO since 2004

17. NITROGEN DIOXIDE POLLUTION MEASURED FROM SPACE BY OMI13 x 24 km pixelsUSED to CONSTRAIN SOURCES March 2006

18. MAPPING OF REACTIVE HYDROCARBON EMISSIONS FROM SPACEusing measurements of formaldehyde columns Millet et al. [2008] 340 nm hydro- carbons formaldehyde Biogenic isoprene is the main reactive hydrocarbon precursor of ozone …and a major source of organic particles Jacob slide

19. Model inversion of CO sources using data from three satellite instruments – Kopacz et al., 2010 AIRS MOPITT Annual emissions Correction factors from inversion TES SCIAMACHY Errors of up to a factor of 2!

20. GEOS-4 model MLS data CO data for the upper and lower troposphere: a test of model transport CO (ppb) at 200 hPa J. Liu, draft paper Oct • Fires in Aug/Sept. are a large source of CO • satellite CO data show timing is correct in the lower troposphere • Convection moves south in October, lifting CO to the UT • model peak is 1-3 months too late (GEOS-5 is worse than GEOS-4) • Detailed analysis shows: • convection over South America detrains at too low an altitude • too strong export of CO to the eastern Pacific in Aug./Sept • isoprene is too large a source of CO • These transport problems will impact inversion studies, which cannot account for systematic errors in transport Nov

21. 1970 1980 1990 2000 2010 Concluding remarks • CTM studies often identify significant problems with model transport – but they don’t necessarily lead to improvements in parameterizations inherent in global GCMs – an issue for 20+ years – 2 communities • Need for a holistic approach with satellite data – a tendency for one species per paper, and global data for CO, O3, NO2, HCHO, aerosols now available (also CH4) • CTMs now used for policy – e.g., long-range transport from Asia to the US, the US to Europe • Coupled chemistry-climate models used for projections • The stakes high – we would like to get things right!