In support of the first Tropospheric Ozone Assessment Report (TOAR) a relational database of global surface ozone observations has been developed and populated with hourly measurement data and enhanced metadata. A comprehensive suite of ozone data products including standard statistics, health and vegetation impact metrics, and trend information, are made available through a common data portal and a web interface. These data form the basis of the TOAR analyses focusing on human health, vegetation, and climate relevant ozone issues, which are part of this special feature.Cooperation among many data centers and individual researchers worldwide made it possible to build the world's largest collection of in-situ hourly surface ozone data covering the period from 1970 to 2015. By combining the data from almost 10,000 measurement sites around the world with global metadata information, new analyses of surface ozone have become possible, such as the first globally consistent characterisations of measurement sites as either urban or rural/remote. Exploitation of these global metadata allows for new insights into the global distribution, and seasonal and long-term changes of tropospheric ozone and they enable TOAR to perform the first, globally consistent analysis of present-day ozone concentrations and recent ozone changes with relevance to health, agriculture, and climate.Considerable effort was made to harmonize and synthesize data formats and metadata information from various networks and individual data submissions. Extensive quality control was applied to identify questionable and erroneous data, including changes in apparent instrument offsets or calibrations. Such data were excluded from TOAR data products. Limitations of a posteriori data quality assurance are discussed. As a result of the work presented here, global coverage of surface ozone data for scientific analysis has been significantly extended. Yet, large gaps remain in the surface observation network both in Schultz et al: Tropospheric Ozone Assessment Report Art. 58, page 2 of 26 terms of regions without monitoring, and in terms of regions that have monitoring programs but no public access to the data archive. Therefore future improvements to the database will require not only improved data harmonization, but also expanded data sharing and increased monitoring in data-sparse regions.

We describe and show results from a series of field campaigns that used balloonborne instruments launched from India and Saudi Arabia during the summers 2014–17 to study the nature, formation, and impacts of the Asian Tropopause Aerosol Layer (ATAL). The campaign goals were to i) characterize the optical, physical, and chemical properties of the ATAL; ii) assess its impacts on water vapor and ozone; and iii) understand the role of convection in its formation. To address these objectives, we launched 68 balloons from four locations, one in Saudi Arabia and three in India, with payload weights ranging from 1.5 to 50 kg. We measured meteorological parameters; ozone; water vapor; and aerosol backscatter, concentration, volatility, and composition in the upper troposphere and lower stratosphere (UTLS) region. We found peaks in aerosol concentrations of up to 25 cm–3 for radii > 94 nm, associated with a scattering ratio at 940 nm of ∼1.9 near the cold-point tropopause. During medium-duration balloon flights near the tropopause, we collected aerosols and found, after offline ion chromatography analysis, the dominant presence of nitrate ions with a concentration of about 100 ng m–3. Deep convection was found to influence aerosol loadings 1 km above the cold-point tropopause. The Balloon Measurements of the Asian Tropopause Aerosol Layer (BATAL) project will continue for the next 3–4 years, and the results gathered will be used to formulate a future National Aeronautics and Space Administration–Indian Space Research Organisation (NASA–ISRO) airborne campaign with NASA high-altitude aircraft.

[1] We present results from complimentary measurements of physical and optical properties of aerosols carried out at Delhi, as part of the Indian Space Research Organization Geosphere Biosphere Programme's Land Campaign II in December 2004. For the first time we unravel ground truth values of several radiatively important aerosol parameters such as their wavelength dependency in absorption, scattering behavior, singlescattering albedo, number size distribution, and vertical distribution in the atmosphere from this polluted megacity in south Asia. Interesting features are observed in the behavior of aerosol parameters under intermittent foggy, hazy, and clear-sky conditions prevalent during the campaign. All aerosol parameters exhibited a large distribution in their values, with variabilities being particularly higher on hazy and foggy days. The average clear-sky aerosol optical depth (AOD) value is 0.91 ± 0.48, which is higher than the AOD value reported for most other cities in India during this season of the year. Increases in AOD on hazy and foggy days are found to be spectrally nonuniform. The percentage increase in AOD at shorter wavelengths was higher on hazy days compared to clear days. Diurnally averaged BC mass concentration varied from a low of 15 mg/m 3 during clear days to a high of about 65 mg/m 3 on hazy days. The wavelength dependency of aerosol absorption shows signatures of the presence of a significant amount of absorbing aerosols produced from biofuel/biomass burning. Single-scattering albedo at 525 nm is found to vary between 0.6 and 0.8 with an average value of 0.68 for the entire period. Lidar observations reveal that during a fog event there is a subsidence of aerosols to an extremely dense and shallow atmospheric layer of less than 200 m height from the surface. The presence of an aerosol layer at elevated altitudes is also detected. All the results are combined and used for estimating aerosol radiative forcing using a discrete ordinate radiative transfer model. We find a large negative forcing at the surface level in the range of À40 to À86 W/m 2 , while forcing at the top of the atmosphere varied between À2 and +3 W/m 2 .Citation: Ganguly, D., A. Jayaraman, T. A. Rajesh, and H. Gadhavi (2006), Wintertime aerosol properties during foggy and nonfoggy days over urban center Delhi and their implications for shortwave radiative forcing,

[1] We present results on various physical and optical properties of aerosols measured over Ahmedabad, an urban location in western India, from 2002 to 2005 and discuss their seasonal and interannual variabilities. Aerosol parameters which have been studied include AOD spectra, aerosol mass concentration, size distribution, BC concentration, wavelength dependency in absorption, scattering coefficient, single scattering albedo and their vertical distribution in the atmosphere. All data have been classified in terms of four major seasons, namely, dry, premonsoon, monsoon and postmonsoon. AODs show an increasing trend over the first half of the year, and this is more consistent at higher wavelengths. Variation of Angstrom parameter a shows dominance of smaller size particles during dry and postmonsoon seasons while increase in coarser particle concentration during premonsoon and monsoon seasons. PM10 mass concentration varied from low values close to 40 mg/m 3 to highs of about 106 mg/m 3 . Size distribution patterns of near surface aerosols exhibited presence of three distinct modes, all of which could be fitted using three lognormal modes. Highest values of BC mass are obtained during postmonsoon (7.3 ± 3.7 mg/m 3 ) while lowest values are measured during monsoon season (1.5 ± 0.8 mg/m 3 ). Wavelength dependency of aerosol absorption shows signatures of presence of significant amount of absorbing aerosols produced from biofuel/biomass burning in the atmosphere. Single scattering albedo at 0.525 mm are found to be 0.73 ± 0.1, 0.84 ± 0.04, 0.81 ± 0.03 and 0.73 ± 0.08 during dry, premonsoon, monsoon and postmonsoon seasons, respectively. Vertical distributions of aerosol for dry and postmonsoon seasons are characterized by high values of extinction coefficients within first few hundred meters from the surface where we find a sharp decrease in the extinction values with increasing altitude. Vertical distribution of aerosols during monsoon season shows presence of a very thick and stable aerosol layer between 0.5 and 2.0 km, contributing significantly to the columnar AODs.Citation: Ganguly, D., A. Jayaraman, and H. Gadhavi (2006), Physical and optical properties of aerosols over an urban location in

[1] Extensive measurements of various aerosol parameters including single scattering albedo (SSA) were made at various locations over the central Indian region during February 2004 to study their impact on the regional aerosol radiative forcing. An overall increase in the measured value of SSA is noticed (0.75 to 0.9) over the period of this campaign, indicating unequal changes in source strength or removal processes of absorbing and scattering types of aerosols. Diurnally averaged value of direct SW radiative forcing for the region is in the range of À15 to À40 W/m 2 at the surface, about 15% lower compared to that over the Bay of Bengal region and 22% higher than over the Arabian Sea. TOA forcing is in the range of +0.7 to À11 W/m 2 , about 50% lower compared to both these regions. This results in a heating rate of nearly 0.8 K/day for the first 2km in the atmosphere. Citation: Ganguly, D., H. Gadhavi, A. Jayaraman, T. A. Rajesh, and A. Misra (2005), Single scattering albedo of aerosols over the central India: Implications for the regional aerosol radiative forcing, Geophys.