A12A-01
A Climate Change Penalty in Pollution Ozone Observed over the Eastern US
Numerical models predict that increasing temperatures due to greenhouse gas-induced climate change will increase ozone air pollution in some regions of the United States. We present evidence that an increase in ozone as a result of increasing temperatures is already observable in the Eastern US. We investigate 21 years of rural ozone observations (millions of hourly average values) spatially grouped into chemically coherent regions. We show that regional ozone amounts declined overall due to the decreasing power plant NOx emissions resulting from the Acid Rain Program and NOx SIP call. By constructing conditional ozone distributions for selected temperature bins we find a robust, nearly linear relationship for temperatures between 10 and 40°C. The slope was 3.2 ppb O3 per °C for 2002 and earlier, but fell to 2.2 ppb per °C after major emission reductions. For the period of 1987 to 2007 observed temperatures increased by 0.51 to 0.68°C, and the ozone temperature relationship indicates a climate change penalty for the mid-Atlantic region of between 1.1 and 2.2 ppb of ozone.
A12A-02
Using satellite data for evaluating the coupled WRF-CMAQ modeling system for use in studying the impact of climate change on air quality in the Western United States
Among the most important concerns in the assessment of the impact of future climate change on human and natural sectors is its effect on future air quality. We will show results of study using satellite remote sensing data from the NASA Tropospheric Emission Spectrometer (TES) and Atmospheric Infrared Sounder (AIRS) satellite instruments in conjunction with surface monitoring station data, to evaluate a regional climate-air quality modeling system in which the Community Multiscale Air Quality (CMAQ) model is one-way nested within the Weather Research and Forecast (WRF) model. The study is a part of preliminary investigation assessing the impact of global climate change on regional air quality, with an emphasis on California, which includes development of a scalable regional climate modeling system. Evaluation of a climate modeling system is a crucial step in assessing the climate change impact because the uncertainties in regional modeling systems are among the major sources of uncertainties in the resulting assessment. The data from TES and AIRS will be used to evaluate the meteorological fields generated by WRF and the air pollutant fields calculated by CMAQ. Information gained from the evaluation study will be used to assess model performance and to improve the modeling system. After the evaluation phase of the project is complete, the regional climate-air quality modeling system will be ready for use in the assessment of the effects of climate change on air quality in California using the scenarios generated by global climate models. We will show results from the model evaluation phase of the project and discuss the future climate scenario modeling that will be performed. The work is being done as a combined effort between UCLA and JPL as part of the UCLA Joint Institute For Regional Earth System Science and Engineering (JIFRESSE) development of a regional earth system model.
A12A-03
Lightning and anthropogenic NOx sources over the U.S. and the western North Atlantic Ocean: Impact on tropospheric O3 from space-borne observations
We use the Regional chEmical trAnsport Model (REAM) to analyze the contributions of lightning and anthropogenic NOx on ozone concentrations over the U.S. and the western North Atlantic Ocean from June to August 2005. Tropospheric NO2 columns from OMI, tropospheric O3 columns derived from OMI and MLS measurements, and vertical O3 profiles from TES over the region are used in the analysis. With a 50% reduction in the industrial and electrical power generation NOx emissions in the 23 eastern states over the U.S. from 1999 EPA NEI and a parameterization of lightning-produced NOx based on concurrent NLDN, CAPE, and cloud mass flux data, REAM generally captures the spatial distribution of lightning flash rates and OMI NO2 and OMI-MLS O3 column enhancements with high correlation coefficients (0.6-0.9). The model results show that over the U.S., the contribution of surface NOx emissions to summertime tropospheric O3 declines from 47% to 41% due to the reduced emissions. The contribution of surface NOx emissions becomes similar to that of stratospheric transport over the U.S., with the additional being the dramatic reduction in the relative impact of fossil-fuel NOx emissions over continental outflow regions. In the convective outflow regions over the Gulf of Mexico and the western North Atlantic, the contribution of lightning NOx production on tropospheric O3 in the summer is larger than that of anthropogenic NOx emissions with mean differences of 5% to 25%. The impact of NOx produced by lightning is becoming larger as fossil-fuel combustion NOx emissions decrease. After the onset of the North American monsoon, lightning-derived upper tropospheric O3 enhancements in July and August are shown over the convective outflow regions from REAM simulated and TES measured O3 vertical profiles. This result suggests that TES measurements have a potential to constrain lightning-derived tropospheric O3 enhancements, which may play a critical role in controlling climate.
A12A-04
On the Use of Boundary Layer NO2 Observations From an Airborne Platform for Satellite Validation
Tropospheric NO2 columns have been measured from space since the mid 1990s. The OMI instrument has been achieving global coverage daily since 2005, providing an incredible resource for addressing long- standing issues concerning global NOx emissions, chemistry and transport. Accurate retrievals are highly dependent on the use of correct a priori vertical distributions of NOx. Comparison of retrieved column densities with in situ aircraft data provides a direct method for evaluating the quality of satellite observations. Extensive use has been made of NO2 data collected by UC Berkeley aboard the NASA DC-8 during four different campaigns between 2005 and 2008 (Boersma, et al, 2008, Bucsela et al, 2008) but has thus far been limited to ascents and descents that span from the boundary layer to near the tropopause to minimize the need for extrapolation. The vast majority of the NO2 tropospheric column, however, is confined to the planetary boundary layer such that a reasonably accurate integrated column can be inferred from a boundary layer height and concentration alone. Here we describe the use of all boundary layer observations from the PAVE, INTEX-B, TC4 and ARCTAS campaigns to calculate integrated tropospheric NO2 columns for comparison to coincident satellite observations. The observations range from the equator to the North Pole between 175 and 289 degrees longitude and include winter, spring and summer measurements. This analysis greatly increases the number of available validation opportunities and allows us to investigate the influence of a variety of factors on retrieved column densities. An assessment of the accuracy of OMI retrievals based on this comparison is reported.
A12A-05 INVITED
Recent Trends in the Atmospheric Methane Burden
Atmospheric CH4 is a strong greenhouse gas and it affects background air quality because it is a precursor for O3 production. Because it has a relatively short lifetime (~9 years), it has a GWP over 20 years of 72, and reductions in emissions can be cost effective, it is a good target for short-term reductions in radiative forcing. Emission reductions must be verified through atmospheric observations; studying interannual variability in CH4 growth rate provides a means to test our overall understanding of the processes responsible for CH4 emissions, and ultimately to test the ability of our observing system for use in verification. From 1999 to 2006, the global burden of atmospheric CH4 remained nearly constant. A simple explanation for the stabilization of atmospheric CH4 remains elusive, and it is likely the result of many contributing factors. During 2007, CH4 increased globally by 7.5 ppb, providing another in a series of anomalies in CH4 growth rate since ESRL measurements began in 1983. Changes in CH4 growth rate are usually associated with changes in [OH], biomass burning, or wetland emissions. This anomaly coincides with the warmest year on record globally, when the Arctic was 4°C above average and Arctic sea ice was at its lowest recorded extent. When these unusual climatic conditions are coupled with estimates that suggest as much as 900 Tg C is stored in permafrost, it is tempting to attribute the cause of the increase in CH4 growth rate to increased emissions from Arctic wetlands. Measurements of CO in the same samples measured for CH4 suggest that biomass burning was not relevant. Measurements of δ13C in CH4 from Alert, Canada are consistent with greater than normal emissions from wetlands.
A12A-06 INVITED
Trends and seasonal cycle of the tropospheric methane observed and modeled over Siberia
We analyzed 12 years of atmospheric methane data observed over West Siberia and compared with models of atmospheric transport and chemistry. The observational data were obtained by flask sampling and laboratory analysis. The samples were taken at the altitude range of 0.5 to 7 km once a month near Surgut and Novosibirsk. The purpose of this study was to compare simulated concentration time series with observed ones is order to evaluate existing surface methane emission estimates for the region. We conducted model simulations with three different chemical tracer transport models using seasonally varying methane emissions (without inter-annual variability). In the lower troposphere, seasonal cycle and trends are obscured by large synoptic scale variability, exceeding seasonal cycle amplitude and inter-annual variability. To reduce the effect of the variability we use multi-year average seasonal cycle in the comparison between models and observations. Observations and models suggest the methane concentration in lower troposphere is significantly different from the free troposphere in response to regional emissions. There is an indication of the large emissions in late summer in the observed seasonal cycle over Surgut. To improve a seasonal cycle fit we need improved surface methane flux models, properly accounting for amplitude and seasonality of emissions.