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.

The composition of airborne particulate matter (PM) varies widely depending on its source, and recent studies have suggested that particle-associated adverse health effects are related to particle composition. The objective of this study was to compare the biological/toxicological effects of different source-related PM. Specifically, we investigated the biological/toxicological effects of standard reference materials (SRMs): non-ferrous dust (PD-1, industrial), urban PM (UPM, SRM1648a), and diesel PM (DPM, SRM2975), and ambient PM(2.5) (PM with an aerodynamic diameter <2.5 µm) collected at an urban site (Toronto, Canada). The dithiothreitol assay was used to measure the redox activity of the particles. Human alveolar epithelial cells (A549) were exposed to a range of concentrations (10-1000 µg/ml) of total PM, and the respective water-soluble and insoluble fractions, for 24 h. Biological responses were then evaluated in terms of cytotoxicity and interleukin (IL)-8 release, and compared with the PM composition and redox activity. We demonstrated that transition metal-enriched PD-1 exhibited the greatest cytotoxic effect (LD(50) values of 100-400 µg/ml vs. >1000 µg/ml for the SRM1648a, SRM2975, and ambient PM(2.5)). Similarly, the PM-induced release of IL-8 was greatest for PD-1 (~6-9 ng/ml vs. ~1.5-3 ng/ml for others). These endpoints were more responsive to metals as compared with compared with secondary inorganic ions and organic compounds. Interestingly, we demonstrated a high degree of adsorption of IL-8 to the various SRMs and ambient PM(2.5), and subsequently derived a new correction method to aid in interpretation of these data. These characteristics likely impart differential effects toward the toxic and immune effects of PM.

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