Ozone Distribution in the Middle Latitude Mesosphere as Derived From Microwave Measurements at Lindau (51.66 N, 10.13 E)
Mesospheric ozone measurements between 50 and 80 km altitude by means of the microwave technique were carried out in middle latitude at Lindau (51.66 N, 10.13 E), Germany, between 1993 and 2006, with an interruption from 1997 to 1998. We utilize data obtained between 1998 and 2006. The measurements show a tendency of typical ozone features that occurs in each year. The most marked patterns are a late summer maximum of ozone in the middle and lower mesosphere which is shifted into autumn and winter in the stratopause region, and a distinct nighttime maximum around 72 km during the winter season, whereas in principle no annual maximum occurs there during daytime. A clear annual asymmetry of the nighttime ozone distribution exists in this domain, marked by a decline of the mean ozone values in January/February and an increase to a subsidiary annual maximum a few kilometers higher in March/April. This asymmetry at the height of the well-known middle mesospheric maximum of ozone (MMM) results from the asymmetric occurrence rate of sudden stratospheric warmings (SSWs) occurring more frequent after winter solstice than before. Additionally, the asymmetric annual variation of water vapor with lowest values just around spring equinox influences the annual variation of ozone. The night-to-day ratios (NDRs) in the middle to upper mesosphere display a distinct winter anomaly marked by values more than twice as high as in summer. The NDR is modulated by pronounced oscillations with a planetary time scale. The maximum effect occurs at 65 to 70 km, clearly below the height of the MMM.
Evidence of transport of ozone from the Indo-Gangetic Plain over the Bay of Bengal
Extensive measurements of vertical distribution of ozone along with meteorological parameters were performed over the Bay of Bengal (BoB) as a part of an Intensive Campaign for Aerosols, gases and Radiation Budget (ICARB) from 19th March to 12th April 2006. A total of 12 balloon flights carrying ozone and radio sondes were conducted over Bay of Bengal (BoB). Based on wind regime prevalent during this period, this region was subdivided into Northern-BoB (closer to Indian mainland along with wind flow) and Southern- BOB (wind flow from open ocean). The derived meteorological parameters (virtual potential temperature, specific humidity, equivalent potential temperature, saturation equivalent potential temperature etc) were used to extract information about the structure of boundary layer. These parameters reveal the presence of additional mixed layer sandwiched between marine boundary layer and trade wind inversion over N-BoB. The ozone concentration was observed to be very high (~ 70 ppb) in this region. The seven day back-trajectory analysis show the advection of air rich in either ozone pre-cursors or ozone itself from highly polluted Indo-Gangetic Plain (IGP). The residence time estimation indicates that the polluted air parcels have spent longer time over the IGP before reaching the flight locations. The secondary mixed layer was absent over S-BoB, where the air was mainly influenced by local marine air. The average vertical ozone (surface to around 2 km) over N-BoB is twice that of over S-BoB. This is a clear example of N-BoB being polluted by transport from the IGP. These results will be discussed in detail during the presentation.
Assessment of the GEM-AQ Model Lightning and Emission Fields During the INTEX-A Field Campaign.
The Global Environmental Multiscale Air Quality model (GEM-AQ) is a tropospheric chemistry, general circulation model based on the global multi-scale model for operational weather forecasting developed by the Meteorological Service of Canada. We compare GEM-AQ with observations made during the first phase of the Intercontinental Chemical Transport Experiment (INTEX-A) campaign conducted mostly over North America and the North Atlantic during the summer of 2004. GEM-AQ was run on a global variable-resolution grid with a 0.5-degree uniform core domain covering Eastern Canada and United States, and 28 hybrid levels extending from the surface up to 10 hPa. The GEM-AQ representation of biogenic, anthropogenic, biomass burning, and lightning NOx emissions and of transport processes such as mixing in the PBL and large scale convection is assessed in a comparison with the measured mixing ratios of O3, NO, NO2, HNO3, H2O2, CO, CH3OH, HCHO, C5H8, C2H6, and HCN.
Detection of SO2 in the Plume of Volcán Turrialba From Ozonesonde Measurements: An Update
Turrialba volcano is located in Costa Rica at 10.0°N, 83.8°W and 3340 m a.s.l. It had been quiescent since a series of eruptions that occurred in 1866 that were sometimes accompanied by pyroclastic flows. Fumarolic activity continued at the summit craters and has intensified since 1996; their maximum intensity was in the period from 2006 - 2007. Due to its record of explosive eruptions, location, height and meteorological factors this volcano represents a significant threat to the Central Valley and during the latter period it has greatly affected the ecological, social and economic development of the region. Vertical profiles of ozone have been made on a regular basis since July 2005 at Alajuela, Costa Rica (10°N, 84.2°W, 883.5 m a.s.l) using balloon-borne electrochemical concentration cell (ECC) ozonesondes, combined with standard radiosondes and occasionally Cryogenic Frostpoint Hygrometer. Soundings are launched one per week and typically reach 30 km altitude. Since high concentrations of SO2 interfere with the reaction between ozone and the potassium iodide solution in the ECC ozonesonde, these profiles can be used to detect volcanic activity. Between 20 December 2007 and 1 February 2008, half of the soundings showed layers below 4 km up to 1 km thick with SO2 amounts in excess of 20 ppbv. This is the highest frequency of such observations since the beginning of ozone soundings in 2005. During this period an increase in the fumarolic activity of the Turrialba volcano was observed. In addition OMI satellite SO2 data showed that its plume was moving west, in the direction of the launch site at Alajuela. During 2008 tropospheric ozone concentrations increased again, and the fumarolic activity at the volcano appears to have diminished in intensity. Taken together, these observations suggest a significant decline in the levels of SO2.
Quantifying the impact of aggregation errors and model biases on top-down estimates of carbon monoxide emissions using satellite's observations
We conducted an inverse analysis of atmospheric CO, using the GEOS-Chem model and observations from the MOPITT satellite instrument, to quantify the potential contribution of model error and aggregation errors to top-down source estimates. We focus on quantifying CO emissions for the biomass burning season of 2000. Using a 4-dimensional variational data assimilation scheme, we optimize the CO emissions on the 2°x2.5° grid of the model. The high-resolution, a posteriori source estimates are compared with estimates obtained from a coarse resolution, analytical Bayesian inversion to quantify the impact of aggregation errors in the coarse resolution inversion on the source estimates. We also carry out the coarse resolution analytical inversion using two different versions of the GEOS-Chem model, driven with different transport fields, to isolate the impact on the source estimates of systematic differences in transport in the models.
Interannual variations in summertime easterly transport of Asian pollution
Previous studies have shown that transport of pollution from Asia has a significant influence on the summertime ozone abundance over the Middle East, North Africa, and the Mediterranean region. We investigate the internannual variability of this easterly transport of Asian pollution between 1986 and 2006 using the GEOS-Chem global chemical transport model, which is driven by assimilated meteorology from the Goddard Earth Observing System (GEOS-4). We find that the year-to-year variations in ozone transport are associated with the Tropical Easterly Jet, which is linked to the strength of the Tibetan High. The variability in the transport is closely related to the Asian Monsoon, indicated by a correlation coefficient of 0.69 with the Webster-Yang Index at a 95 % significance level. We find that the transport weakens during the analysis period, in agreement with the trend in weakening of the summer Asian Monsoon.
Signature of Cities in the Tropospheric Ozone Columns Obtained by the Empirically Corrected Tropospheric Ozone Residual Technique From TOMS/SBUV Measurements
Tropospheric ozone is an important greenhouse gas in the upper troposphere and is also a precursor of OH radicals, thus strongly influencing tropospheric chemistry. At the surface, it is a pollutant and is the primary component of photochemical smog. As such it is one of the key trace gases that future satellite missions like the GEO CAPE (Geostationary Coastal and Air Pollution Events) mission will measure. It is thus important to carefully assess the capability of the existing satellite data products for possible air quality applications to set the stage for such missions. There is a long heritage of satellite based methods that subtract the stratospheric column from the total ozone column measured to estimate the tropospheric ozone residual (TOR). The TOR values obtained by the empirically corrected technique (Fishman et al., Atmos. Chem. Phys.,3, 893, 2003) from TOMS/SBUV measurements show regional level enhancements that correlate with population density in various parts of the globe. In this study, we show that distinct signatures of city-scale ozone pollution can also be detected in this data set. Case studies of enhanced TOR plumes observed in the downwind areas of several large polluted cities will be presented. Corresponding NO2 tropospheric columns from the SCIAMACHY instrument are consistent with these urban plumes. Such plumes, however, are not seen at all times. Our preliminary results indicate that detection of these plumes is correlated with local convection, which effectively transports boundary-layer pollution to higher altitudes where TOMS sensitivity to ozone is enhanced. These results may have important ramifications for future air quality studies using residual techniques.
Improving Numerical Instability of the Assimilation of Nadir Profile Retrievals of Tropospheric Ozone From the TES Instrument Into the GEOS-Chem Model
The first ozone observations with the Brewer spectrophotometer at the South Pole
In February of 2008, Environment Canada in cooperation with National Oceanic and Atmospheric Administration installed the Brewer ozone spectrophotometer, serial number #085, at the Amundsen-Scott South Pole Station, Antarctica. The Brewer spectrophotometer (the Brewer) is a fully automated instrument, which allows continuous 24-hour a day direct-sun observations at the South Pole from September to March and periodic moon observations for the remainder of the year. Brewer #085 has been independently calibrated before its deployment at the South Pole and the internal tests from the instrument show that the instrument has been stable for the past year. Brewer #085 has now collected more than a year worth of data. Both the direct-sun and moon observations have been processed and analyzed. The results of this analysis are presented and discussed.
Impacts of biogenic emissions on summertime ozone episodes in North America: GEM-AQ simulation of the August 2007 heat wave
Long-term changes in air quality from the past to the future occur not only by changing anthropogenic emissions but also by changes in photochemical activities, transport, and natural emissions from forest fires and terrestrial vegetation induced by climate change. For example, it has been speculated that forest fire and biogenic emissions will increase with global warming in the northern mid- and high-latitudes potentially to exacerbate summertime air quality despite anthropogenic emission measures. To address synergies between these factors in the context of Canada's air quality trends, we are upgrading our air quality model, GEM-AQ (Global Environmental Multiscale Air Quality model) including the implementation of the online terrestrial biogenic emission model MEGAN (Model of Emissions of Gases and Aerosols from Nature). This will add a capability to the GEM-AQ model of simulating changing biogenic emissions due to climate change. Initial evaluation of the MEGAN emissions as implemented to GEM-AQ is performed by simulating a case for the August 2007 heat wave in North America. We will show how MEGAN improves GEM-AQ's capability by using surface ozone measurements across North America as well as column density measurements of HCHO and NO2 from the OMI satellite.
Ozone Concentrations Patterns over the Metropolitan Area of São Paulo, Brazil
Eleven years of ozone concentrations were analyzed in order to characterize the tropospheric ozone behavior since 1996 up to 2006 over the Metropolitan Area of São Paulo (MASP). MASP covers an area of 8.051 square kilometers, where approximately 19 million people live, and represents the most important economic region of Brazil. The main sources of pollutants in the MASP are the vehicles, which are responsible for more than 95% of CO, NOX and HC emission according to the São Paulo State Environmental Agency (CETESB). These pollutants are strictly correlated with ozone formation through a complex mechanism that depends mainly on a nonlinear mixture of volatile organic compounds (VOC) and nitrogen oxides (NOx). The ozone concentrations are also affected by meteorological conditions, as solar radiation that will be important for the photolysis, and by transport processes from/to other regions. The established maximum hourly National Air Quality Standard (NAAQS) for ozone is frequently violated in the MASP. According to CETESB, during the last five years the annual average of NAAQS violations was 65 days. It is important to emphasize that during this period a substantial increase in the number of vehicles was observed. So far, there is no study available in the literature which evaluates the complete historical time series of the ozone concentration data collected in the air quality monitoring network of the MASP. In this study, data from 12 air quality monitoring stations distributed over the MASP were evaluated. In general, annual mean concentrations of primary pollutants decreased on the last two decades mostly due to the Brazilian Vehicular Emission Control Program (PROCONVE). The program by itself was responsible for a drop of almost 70% of vehicular emissions. However, ozone annual mean concentrations do not reveal the same trend. Among 10 air quality monitoring sites four of it presented a reduction of ozone concentration values while the others six presented an increased tendency. Also, ozone mean concentrations presented an increase during weekends. This increase was about 11% during Saturdays and 20% on Sundays and it was observed in all stations over the area, being more significant in stations influenced by heavy traffic, especially of trucks or buses. The higher ozone concentrations were found during the afternoon, between 14 and 15 LST in all stations, in response to the time of maximum solar radiation incidence, which occurs a few hours early. During nighttime, ozone concentrations presented a fast reduction, mainly because of dry deposition on the surface and to the lost during chemical reactions (e.g., ozone molecule consumption by the reaction with nitrogen monoxide molecule).Although the absence of solar radiation incidence during nighttime, causing a sharp drop on ozone concentrations, a secondary peak can be observed in ozone concentrations around 03 and 04 LST over the region, which can be explained by transport (horizontal and vertical) from other regions as reported in many previous studies.
Simulation of a Multi-day Ozone Episode in the Metropolitan Area of São Paulo, Brazil
High concentration values of ozone are commonly observed over the metropolitan area of São Paulo (MASP). According to the state environmental agency (CETESB) violations to the National Air Quality Standards (NAAQS) were reported on 72 days during 2007. Over 19 million people live in the MASP and the vehicular fleet has more than 7 million vehicles responsible for almost 95% of CO, NOX and hydrocarbons emissions. In this study, a prolonged ozone episode observed in the area was simulated with the Simplified Photochemical Model coupled with the Brazilian version of the Regional Atmospheric Modeling System (SPM- BRAMS). The simulated photochemical episode started in October 3rd, 2002 and lasted for 14 days. During this period, hourly ozone concentration reached values over than 300 μ g.m-3. During 10 days of those 14, more than 60% of the air quality monitoring sites presented ozone levels above the NAAQS. Two nested grids with a horizontal resolution of 16 and 4 km were used in order to evaluate the meteorological conditions related with this extreme air pollution event. Several meteorological variables were extracted from the model simulation. Ozone concentration values simulated by the SPM were also used to support the analysis. During the simulation period, the MASP was under the influence of a high pressure system associated with clear sky conditions and calm winds. Meso-scale circulations were favored due to this synoptic pattern and the sea breeze influence, transporting the photochemical plume to northwest of the region, could be identified during all days of the simulation. During some days even the effect of the land breeze, transporting the plume to the seashore, located about 60 km southeast from the center of the grid, was verified. The planetary boundary layer (PBL) height simulated by the SPM-BRAMS model showed lower values during days when the worst air quality conditions were registered by the existent monitoring network. High temperatures and low relative humidity rates were also observed through the model results. During the entire period, precipitation was not produced by the model. All these factors contributed to the occurrence of the multi-day ozone episode considered in this work.