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The influence of methane emission variability on tropospheric NO x recycling

The influence of methane emission variability on tropospheric NO x recycling. J. E. Williams, M. van Weele and P. F. J. van Velthoven Chemistry & Climate Division, KNMI The Netherlands. The link between CH 4 and O 3. Fiore et al, JGR, 2008.

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The influence of methane emission variability on tropospheric NO x recycling

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  1. The influence of methane emission variability on tropospheric NOx recycling J. E. Williams, M. van Weele and P. F. J. van Velthoven Chemistry & Climate Division, KNMI The Netherlands

  2. The link between CH4 and O3 Fiore et al, JGR, 2008 Multi-model ensemble of response of O3 to CH4 emissions IPCC 2007

  3. Mechanism: Methane and NOx recycling OH + CH4 (+ O2)  CH3O2 + H2O (1) CH3O2 + NO (+ O2)  NO2 + HCHO + HO2 (2) HO2 + NO  NO2 + OH (3) NO2 + hv (+ O2)  NO + O3 (4) Net: CH4 (+ 4O2)  HCHO + H2O + 2O3 (5) Additional HCHO oxidized to CO enhancing HO2 OH + CO (+ O2)  HO2 + CO2 (6) Termination steps HO2 + HO2 H2O2 (7) OH + NO2 HNO3 (8) OH + HO2 H2O (9)

  4. Constraints on CH4 in global chemistry-transport modeling Traditional No emissions applied 2D (latitude vs month) climatology assembled from NOAA-ESRL background measurement stations Instantaneous forcing at the surface to zonal mean at each lat,lon

  5. Emissions estimates EDGAR 4.0/LPJ-WhyMe combination applied (no Anthro. growth since 2005!) 2D (latitude vs month) climatology assembled from NOAA-ESRL background measurement stations Nudging in lower troposphere to background ratio (@ dateline) using 3 day relaxation time

  6. CTM model simulations (TM5) ● 3D global CTM TM5-chem-v3.0 (Huijnen et al., 2010) ● 3° x 2° with 34 vertical levels (1km resolution in the UTLS) ● Driven by the ERA-interim meterological re-analysis ● Modified CBM4 chemistry : NOx-HOx-CH4-CO-VOC-SOx ● Results part of decadel simulations performed between 2000-2009 ● 2-year spin-up (1998/1999) Non-CH4 emission set-up ● Anthropogenic : RETRO/REAS hybrid accounting for increasing emissions in the REAS region (Ohara et al., ACP., 2007; Schultz et al, 2008) ● Biomass burning: GFEDv2 global fire emission inventory (Monthly/8-day) ● Biogenic : ORCHIDEE 12-year annual average ● Lightning: related to convective precipitation (Meijer, 2001 scaled to 5 Tg N yr-1)

  7. Decadal CH4 emissions : Global Scale Emissions calculated from 2D (lat, lon) fields in chemical budget files from TM5 Global scale perturbation due to nudging Differences in CH4 emissions ranges from 0-15 Tg CH4 yr-1 additional emissions

  8. Zonal decomposition NH and SH : CH4 emissions Increased seasonal cycle Additional source term : +20Tg CH4 yr-1 NH Under estimation : too low emissions in inventories Additional sink term- 20Tg CH4 yr-1 SH Over estimation : Long range transport from source regions Implies : either transport too efficient or chemical lifetime is too long in TM5 (SH) Increased seasonal cycle in NH correlates with enhanced biogenic activity during boreal summer

  9. Increase in regional surface concentrations Anthro. Natural Significant improvements in seasonality near anthro. source regions (hun), in lower trop. (kzd) and background (sey) Small negative diffs away from sources

  10. Perturbations in global CH4 burden : Zonal trends CH4-HYBRID CH4-HYBRID NH: Increase till 2004-2005 (plateau) then decrease TR: Modest increase till 2007 then rapid increase SH : High variability due to lack of emission sources and meteorological variability

  11. Increases in surface O3 from increased NOx re-cycling • Increases of ~0.5% occur • in the tropics where most CH4 oxidized • near China (high NOx regime) • Increases of ~0.1-0.3% occur (i) in the background due to long-range transport away from sources (ii) Near strong natural sources which have lower NOx emissions

  12. Increases in CO via enhanced HCHO production • CH3O2 + NO (+ O2)  NO2 + HCHO + HO2 • OH + HCHO  CO + HO2 • HCHO + hV  CO • HCHO + hV  CO + 2HO2 • ~0.2Tg CO formed per Tg CH4 emitted • thus ~100 Tg CO yr-1 •  Increases of ~0.5-1.0% occur: • (i) In the tropics (high photochemistry) • (ii) Throughout NH where most CH4 emitted • Increases of ~0.2-0.5% occur: (i) In the background

  13. Seasonality in in-situ O3 production (pO3) : CH4-HYBRID For all zonal domains recycling by HO2 dominates O3 production RO2 term most important in NH near high VOC emission sources Strong seasonal dependency due to variations in photochemical activity

  14. Perturbations in pO3 via peroxy channels Increased scavenging for NO by HO2 and CH3O2 reduces RO2 channel across zones High variability in contributions due to different channels in NH Tropics gradual increase in pO3 with increasing BCH4

  15. Normalized O3 production (nO3) (Tg O3 yr-1/Tg CH4 yr-1) NH decreasing trend in nO3 over decade Reduced emissions in SH due to increased transport significantly increases nO3

  16. Conclusions

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