Impact of extreme wildfires from the Brazilian Forests and sugarcane burning on the air quality of the biggest megacity on South America.

Recently, extreme wildfires have damaged important ecosystems worldwide and have affected urban areas miles away due to long-range transport of smoke plumes. We performed a comprehensive analysis to clarify how smoke plumes from Pantanal and Amazon forests wildfires and sugarcane harvest burning also from interior of the state of São Paulo (ISSP) were transported and injected into the atmosphere of the Metropolitan Area of São Paulo (MASP), where they worsened air quality and increased greenhouse gas (GHG) levels. To classify event days, multiple biomass burning fingerprints as carbon isotopes, Lidar ratio and specific compounds ratios were combined with back trajectories modeling. During smoke plume event days in the MASP fine particulate matter concentrations exceeded the WHO standard (>25 µg m-3), at 99 % of the air quality monitoring stations, and peak CO2 excess were 100 % to 1178 % higher than non-event days. We demonstrated how external pollution events such as wildfires pose an additional challenge for cities, regarding public health threats associated to air quality, and reinforces the importance of GHG monitoring networks to track local and remote GHG emissions and sources in urban areas.

Molecular ordering of PAH/MA-co-DR13 azopolymer layer-by-layer films probed by second-harmonic generation.

Molecular orientation within azopolymer thin films is important for their nonlinear optical properties and photonic applications. We have used optical second-harmonic generation (SHG) to study the molecular orientation of Layer-by-Layer (LbL) films of a cationic polyelectrolyte (poly(allylamine hydrochloride)) and an anionic polyelectrolyte containing azochromophore side groups (MA-co-DR13) on a glass substrate. The SHG measurements indicate that there is a preferential orientation of the azochromophores in the film, leading to a significant optical nonlinearity. However, both the signal strength and its anisotropy are not homogeneous throughout the sample, indicating the presence of large orientational domains. This is corroborated with Brewster angle microscopy. The average SHG signal does not increase with film thickness, in contrast to some reports in the literature, indicating an independent orientational order for successive bilayers. Analyzing the SHG signal as a function of the input and output polarizations, a few parameters of the azochromophore orientational distribution can be deduced. Fitting the SHG signal to a simple model distribution, we have concluded that the chromophores have an angular distribution with a slight in-plane anisotropy and a mean polar angle ranging from 45° to 80° with respect to substrate normal direction, with a relatively large width of about 25°. These results show that SHG is a powerful technique for a detailed investigation of the molecular orientation in azopolymer LbL films, allowing a deeper understanding of their self-assembling mechanism and nonlinear optical properties. The inhomogeneity and anisotropy of these films may have important consequences for their applications in nonlinear optical devices.

Study of the properties of aerosols and the air quality index using a backscatter lidar system and AERONET Sunphotometer in the City of São Paulo, Brazil.

Between the months of July and September of 2007 during the so-called Brazilian dry season, an aerosol profiling campaign was carried out with a backscatter(ing) lidar system in the city of São Paulo, Brazil. The main goal of this campaign was to observe the aerosol load in the troposphere (up to 10 km) and its daily behavior to check for air dispersion conditions, planetary boundary, and mixed layer height daily evolution. Lidar analysis provided aerosol optical properties in the visible range (532 nm) and quantities such as aerosol backscatter(ing) and extinction coefficients in conjunction with the aerosol optical thickness provided by a collocated AERONET Sunphotometer. Altogether 61 days were used in the dataset, which were compared with air quality indexation from the local air quality monitoring and management agency.