A54B-01 INVITED
Interannual to millennial variation of biogenic ozone and aerosol precursor emissions
Biogenic volatile organic compounds (BVOC), particularly isoprene and monoterpenes are important precursors for the formation of tropospheric ozone and secondary organic aerosol. But the amount and regional distribution of their emissions are poorly known which makes them one of the chief sources of uncertainty in atmospheric chemistry-climate models. What is more, a number of processes have emerged over recent years that need to be taken into account in simulation experiments and that previously have not been accounted for in global emission estimates. To investigate the transient responses of isoprene and monoterpene emissions over time-scales from inter- annual to millennia BVOC algorithms have to be coupled into dynamic global vegetation models (DGVM) to account for variation in vegetation productivity, phenology and leaf area index as important controls on BVOC emissions. We will present here analyses of isoprene and monoterpene emissions in response to variation in climate and atmospheric CO2 concentration concentrating using a process-based BVOC algorithm within the DGVM framework LPJ-GUESS. The model accounts for the CO2-inhibition of leaf isoprene and monoterpene production. Our analysis concentrates specifically on emission variation over (i) the last two decades and (ii) from the mid- Holocene to the pre-industrial period. These analyses provide novel insight of emission responses to short-term fluctuations in climate, long term trends in climate and atmospheric CO2 concentration and of early human deforestation associated with establishment of agriculture.
A54B-02
Impact of Aerosol-Cloud Interactions on Tropospheric Ozone
Aerosol-cloud interactions may impact tropospheric ozone (O3) directly through modifications to photolysis rates and washout of precursors and indirectly through changes in climate variables such as temperature. Most previous studies of past and future O3 changes have neglected the influence of aerosol-cloud interactions. We apply the NASA Goddard Institute for Space Studies model for Physical Understanding of Composition- Climate INteractions and Impacts (G-PUCCINI) to quantify the impact of aerosol-cloud interactions on O3 radiative forcing and surface air quality for the 2030 A1B future atmosphere relative to 1995. Aerosols simulated include sulfate, organic carbon, black carbon, sea-salt and dust. The aerosol-cloud interactions simulated for liquid-phase stratus and cumulus clouds include (1) the first aerosol indirect effect: increased (decreased) cloud reflectivity due to an increase (decrease) in aerosols and cloud droplet number concentrations and reduced (increased) droplet sizes: and (2) the second aerosol indirect effect: change in cloud cover, cloud liquid water path and precipitation due to smaller droplet sizes that inhibit precipitation processes. For 2030 relative to 1995, the aerosol indirect effect is -0.69 Wm-2 mainly due to increases in cloud liquid water path at the expense of suppressed precipitation leading to increases in cloud optical depth. The global annual mean O3 radiative forcing across this time period is +0.126 Wm-2, 10% less than for experiments that do not consider aerosol-cloud interactions. Our results imply that aerosol-cloud interactions have limited the O3 forcing since the preindustrial. When aerosol-cloud interactions are included, simulated surface O3 at 2030 is decreased across the United States and South Asia and increased across Europe, around 1-2 pbbv on the annual mean. We use the model to explore the effect of the observed global decrease in reflective aerosol since 1990 on tropospheric O3 despite the counteracting influence of air quality control legislation on O3 precursors in the United States and Europe, and the simultaneous decline in the methane growth rate across the same time period.
A54B-03
Climate Effects on Ozone Concentrations in California
The statistical relationship between the daily 1-hr maximum ozone concentrations and the daily maximum upper air temperature was explored for California's two most heavily polluted air basins: the South Coast Air Basin (SoCAB) and the San Joaquin Valley (SJV). The temperature at an elevation of 850-milibar pressure (T850) for the period 1980 – 2004 was obtained from the National Center for Environmental Prediction (NCEP) / National Center for Atmospheric Research (NCAR) Reanalysis1 dataset for Riverside (SoCAB) and Fresno (SJV). Daily 1- hr maximum ozone concentrations were provided by the California Air Resources Board (CARB) for Upland (SoCAB) and Parlier (SJV) for the same time period. The ozone concentrations at any given value of T850 were approximately normally distributed. The 25%, 50%, and 75% quartile ozone concentrations increased linearly with T850, reflecting the effect of temperature on emissions and chemical reaction rates. A 2-D Lagrangian (trajectory) form of the UCD/CIT photochemical air quality model was used to explain the standard deviation of the ozone concentrations at each value of T850. Three-day back trajectories were calculated for a typical air quality episode. The base case trajectory routes were then perturbed by adding stochastic bias to the wind-field. Temperature, relative humidity, mixing height, initial concentrations for VOC concentrations, background ozone concentrations, time of year and overall emissions were also perturbed in a realistic fashion during this study. A total of 62 model simulations were performed and the results were analyzed to show that long term changes to emissions inventories were the largest sources of ozone variability at a fixed value of T850. Projections of future T850 values in California were obtained from the Geophysical Fluid Dynamics Laboratory (GFDL) model under the Intergovernmental Panel on Climate Change (IPCC) A2 and B1 emissions scenarios for the years from 2001 to 2100. The future temperature trends combined with the historical statistical relationships suggest that the number of days with O3>90 ppb would increase by 0.5-0.7 days/year under the A2 emissions scenario and 0.2- 0.3 days/year under the B1 emissions scenario (assuming the emissions remained at 1990-2004 levels). These calculations help to quantify the climate "penalty" that must be overcome to improve air quality in California.
A54B-04
The sensitivity of regional air pollution over the United States to future global climate and anthropogenic emissions changes: Part 1. Ozone
We examined the relative importance of future changes in climate, anthropogenic emissions, biogenic VOC emissions, CH4, and long-range air pollution transport on U.S. O3 by performing a suite of simulations with an an integrated model of global climate, gas-phase chemistry and aerosols. Where applicable we used the A2 2050s climate as a representative future climate, and the A2 2050s (overall U.S. emissions increase) and B1 2050s (overall U.S. emissions decrease) emissions for future emissions. The model simulations show that U.S. O3 is sensitive first and foremost to U.S. anthropogenic emissions changes, best illustrated in the domain- average changes in the average daily maximum 8-hour O3 concentrations (MDA8-O3) over the eastern U.S. (May-September) due to: 1) climate change with present-day anthropogenic emissions (2.1 ppbv); 2) anthropogenic emissions change alone (-9 to 9 ppbv); 3) climate change with different emissions regimes (0.9 to 3.4 ppbv); 4) increased global CH4 concentration only (2.4 ppbv); and, 5) long-range air pollution transport (1.4 ppbv). The 95th-percentile O3 increase (May-September) due to climate change with B1 and A2 emissions is 1 ppbv and 10 ppbv, respectively. Therefore, the O3 effect of climate change is minimized under an emissions reduction scenario and amplified under an emissions increase scenario. Increased CH4 and long-range transport (A2) together contribute 3.8 ppbv to the domain-average MDA8-O3 (May-September), thereby increasing the O3 background over the U.S. With more stringent O3 standards in the future, this increased O3 background could significantly reduce the benefits of likely drastic U.S. emissions reductions over the next several decades.
A54B-05
Climate Response to Global Ozone Changes: Impacts of Tropospheric Ozone Increase and Stratospheric Ozone Decrease During the 20th Century
We study the climate response to changes in global tropospheric and stratospheric ozone (O3) distributions from preindustrial times (PI) to the present day (PD; ~2000) through a set of model simulations. The climate response is evaluated by conducting a pare of equilibrium climate simulations with the CCSR/NIES/FRCGC climate model using PI vs. PD O3. We performed 5 distinct scenario experiments (with 5 ensemble runs for each) to isolate the impacts of (1) increases in long-lived GHGs (LLGHGs), (2) emission-induced increase in tropospheric O3 (TOZ), and (3) halogen-induced decrease in stratospheric O3 (SOZ). Climatologies of the global O3 distributions in PI and PD for each of TOZ and SOZ are generated using the chemistry climate model CHASER with PI and PD precursor emissions and halogen loading. In the simulation, tropospheric O3 burden increases by ~10 DU (0.41 W m-2 radiative forcing) up to the present due to the emission increases (TOZ), but decreases by ~1 DU due to the halogen-induced O3 depletion (SOZ); for SOZ, a large O3 reduction (5-10 ppbv) is calculated in the upper troposphere consistent with the O3 sonde observation in the late 20th century. As an equilibrium response, the TOZ increase causes a global and annual mean surface temperature increase of 0.29 C° (NH:0.31 C°,SH:0.26 C°), equivalent to 13% of the estimated LLGHGs impact (2.27 C°). Responding to TOZ, particularly large warming occurs in North America, Middle East, and Asia, apparently reflecting the spatial distributions of the radiative forcing from TOZ. However, our sensitivity simulation with evenly distributed TOZ increase suggested that such inhomogeneous warming response reflects the sensitivity of our climate model rather than the forcing distributions. The SOZ decrease, causing a decrease in tropospheric O3, leads to a surface cooling of -0.04 C°. Both TOZ and SOZ cause cooling in the lower to middle stratosphere (-0.5-1 C°). LLGHGs similarly cool the upper stratosphere, but warm the lower stratosphere due to the enhanced circulation.
A54B-06
Using the Longitudinal Structure in Ozone Trends to Differentiate Between Chemical and Dynamical Forcing of Ozone
A new collection of high vertical resolution trace gas profiles, with global coverage, has been assembled. The collection includes measurements from different satellite (HALOE, POAM II and III, SAGE I and II) and ground- based measurement systems (ozonesondes, lidar). In addition to the primary products of temperature and ozone, secondary measurements of aerosol extinction, NO2 and H2O are included. All data products are subjected to very strict quality standards and for every measurement an error estimate is stored. To facilitate analyses, three different databases within the collection have been constructed, viz., measurements indexed by:
A54B-07
Semi-Empirical Models of Polar Stratospheric Ozone Depletion and Their Applications
Inter- and intra-annual variability in polar stratospheric ozone depletion is controlled by the interaction of gas- phase chemistry, heterogeneous chemistry, and transport. Two semi-empirical models were developed to relate the conversion of total polar stratospheric chlorine (Cly) to activated chlorine (ClOx), and to then relate the rate of ozone destruction to ClOx. The first semi-empirical model was used to calculate the daily total mass of ClOx through a given season when provided with stratospheric temperature fields and a definition of the vortex edge. The equation is a first order differential equation relating the time rate of change of ClOx to unactivated stratospheric chlorine (Cly - ClOx) multiplied by the fraction of the vortex area containing polar stratospheric clouds and the fraction of the vortex area exposed to sunlight, and to a decay term to account for conversion back to reservoir species. The second semi-empirical model relates the time rate of change of ozone mass deficit (OMD) to the mass of activated chlorine as derived from the first equation, in-situ production of ozone and a term for dynamical entrainment of ozone rich air from lower latitudes into the polar vortex. The coefficients of both equations have been derived by optimally fitting the equations to observations and/or to output from chemistry-climate models (CCMs). The coefficients from these equations capture key sensitivities in the atmosphere that determine the interaction between climate change and polar ozone depletion. Potential applications of these coefficients include intra- seasonal projection of the severity of polar ozone depletion, evaluation of pre-1980 ozone depletion and process oriented validation of CCMs.
A54B-08
Towards an Earth System Model: Validating Interactive DMS Emissions, and the Importance of Making Atmospheric-Chemistry Interactive
We are laying the foundation for an Earth System Model (ESM) focused on the sulfur cycle. This ESM will be based on the Community Climate System Model (CCSM) with a fast atmospheric chemistry & aerosol capability communicating with an ocean sulfur-cycle incorporated into the ocean biogeochemistry module. We will present a validation of the di-methyl-sulfide (DMS) emissions from the ocean component using comparison of observed atmospheric sulfate aerosols with the sulfate aerosols calculated using our atmospheric chemistry & aerosol capability. The interactive ocean sulfur-cycle capability has previously been tuned to the in situ observational database of Kettle et al. (2000), but not to any atmospheric sulfate measurements, so this is an independent validation. We will also present the results of simulations to evaluate the importance of including atmospheric chemistry interactively in long steady-state climate simulations. In particular, we will show the impact on the mean and variance of zonal mean temperature and precipitation.