María Isabel Micheletti

Sensitivity of Biologically Active UV Radiation to Stratospheric Ozone Changes: Effects of Action Spectrum Shape and Wavelength Range {

Abstract Biological action spectra are commonly used to assess health and ecosystem responses to increases in spectral ultraviolet (UV) irradiances resulting from stratospheric ozone (O3) reductions. For each action spectrum, a normalized sensitivity coefficient (the radiation amplification factor [RAF]) can be calculated as the relative increase in biologically active UV irradiance for a given relative decrease in the atmospheric O3 column amount. We use a detailed radiative transfer model to calculate the dependence of RAF on the O3 column amount and the solar zenith angle (and, therefore, implicitly on latitude and season) for several commonly used action spectra. A simple analytical model is used to interpret the results in terms of the semilogarithmic slope of the action spectra in the UV-B and UV-A wavelength ranges. We also show that RAF may be overestimated substantially if the UV-A portion of an action spectrum is significant but is neglected. This is illustrated using several idealized action spectra as well as published action spectra for plant responses to UV irradiation. Generally, if the portion of an action spectrum measured longward of ∼300 nm spans less than about two orders in magnitude in its sensitivity, significant errors in the estimated RAF may ensue, and the use of this action spectrum in O3-related studies can be compromised.

Solar UVB and Plant Damage Irradiances for Different Argentinean Regions

We calculated the integrated UVB and plant damage irradiances for Argentina, a country in the Southern Hemisphere spread over a large latitudinal range. The irradiances were calculated for clear sky days using the Madronich code for the average conditions of the months corresponding to the summer and winter solstices and the fall and spring equinoxes. Ozone, aerosol and ground albedo typical for each region and for each period of the year have been considered. A comparison was made of the behavior of these irradiances at the different locations. A more pronounced time dependence of the plant damage irradiance was obtained because of the fact that the corresponding spectrum is largely concentrated at a small wavelength of the UVB interval. We established a correlation between both irradiances, which can be approximated by a quadratic function. Because the plant damage irradiance is a quantity that is not directly measured by instruments, we showed the utility of the correlation by determining this biological effectiveness from the integrated UVB irradiance measured at the Astronomical Observatory of Rosario, Argentina, on clear sky days of the year 2001, as a characteristic example of the midlatitude near–sea level location of a highly productive agricultural region, which can be extended to other regions of the world. The plant damage results are relative ones (as is the case for the erythemal irradiance). So, they can be used to determine the maximum/minimum and asymmetry ratios, to study the influence of atmospheric variables and to make comparisons with other geographical locations.

Connections between black carbon (soot) emission and global warming

Fil: Piacentini, Ruben Dario Narciso. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Rosario. Instituto de Fisica de Rosario. Universidad Nacional de Rosario. Instituto de Fisica de Rosario; Argentina

Satellite and ground atmospheric particulate matter detection over Tucumán city, Argentina, space-time distribution, climatic and seasonal variability

The analysis of atmospheric particles (aerosols) is of special interest due to their potential effects on human health and other applications. In this paper the climatic and seasonal effects on aerosols have been characterized in Tucuman city (26°50’ S, 65° 13’ W,450 masl),Argentina, for the 2006–2013 period. The atmospheric aerosols in Tucuman city result from both stationary and mobile sources such as: industrial activity of sugar cane and alcohol distilleries, paper industry, biomass burning (mainly sugarcane waste crop and grasslands), household waste burning and transport emissions. The peak of industrial activity is seasonal, coincident with the austral winter (July-August-September), when accumulation of particles in the lower atmosphere occurs. In this region, there are no studies like the present one that evaluate, using “ in situ ” equipment, the temporal variation of aerosols and its causes, by applying modern analytical techniques. A continuous volumetric and isokinetic sampler of Hirst type (Burkard), was used for atmospheric particle sampling, in weekly records between 2006 and 2013. The particle concentration (number of particles per cubic meter) showed an increasing trend in the studied period. The monthly variation of: the particle concentration; the aerosol optical thickness at a wavelength of 550 nm (AOD 550 ) obtained from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensors onboard Aqua (NASA) satellite, and the AOD from different aerosol tracers (black and organic carbon, sea salt, sulfates, dust) obtained from the Modern-Era Retrospective Analysis for Research and Applications (MERRA-2), were also analyzed. The temporal variation in particle concentration was explained mostly by wind direction, while the corresponding variation for AOD 550 (MODIS) was explained by temperature and seasonality (as by-product of climatic variation and anthropogenic particle emission sources). The variation in the AOD 550 (MERRA-2) data series were explained by temperature, humidity, precipitation, and seasonality, with less effect of wind speed and direction. Particle concentration, AOD 550 (MODIS), and AOD 550 (MERRA-2) were highly variable. The cross-correlation between AOD 550 (MODIS) and AOD 550 (MERRA-2) time series was significantly positive at lag zero. Other contribution was the determination of the space-time distribution of aerosols on a monthly basis considering AOD 550 MODIS (3 km × 3 km) data. The present study suggests that these variables are affected by temperature and wind dynamics driven by seasonal and high-order autoregressive non-linear processes.