Recebido em 17/2/06; aceito em 17/7/06; publicado na web em 10/1/07 POLYCYCLIC AROMATIC HYDROCARBONS AS SUGARCANE BURNING TRACERS: A STATISTICAL APPROACH. In this study atmospheric particulates of PAHs were measured in Araraquara, Piracicaba and São Paulo in July 2003 (sugarcane harvest season in Araraquara and Piracicaba) and in Araraquara in March of 2003. The results were normalized to the total PAH concentrations. Comparison among the sites and principal component analysis (PCA) were used to investigate possible tracers of emission. Fluoranthene and pyrene concentrations were higher in Piracicaba and Araraquara samples. These PAH were also responsible for the largest negative loadings on the second principal component and account for the negative scores and for the formation of the Araraquara and Piracicaba group.Keywords: PAH; sugarcane burning; PCA. INTRODUÇÃOEmbora grande produtor de açúcar desde o final do século XVI, o Brasil expandiu muito a cultura da cana-de-açúcar a partir da década de 70, com o advento do PROÁLCOOL, programa desenvolvido pelo governo brasileiro para estimular a produção de etanol, usado como combustível de automóveis. Atualmente, o Brasil possui 4,5 milhões de ha de terra plantados com cana-de-açúcar. A produção brasileira vem aumentando a cada ano. Na safra de 2003/04 foram produzidas 359 milhões de t de cana. O Brasil é o maior produtor de cana-deaçúcar do mundo, seguido por Índia e Austrália. A cana é colhida no Centro-Sul (de maio a outubro) e no Norte-Nordeste (dezembro a maio), o que permite dois períodos de safra. Na média, 55% da cana brasileira gera álcool e 45% açúcar [1][2][3] . O Estado de São Paulo possui 2,35 milhões de ha de terra plantados com cana de açúcar e responde por 60% da produção nacional. São Paulo é também responsável por 64% do álcool e 56% do açúcar produzidos no Brasil 3 . Na época da safra, as plantações de cana-de-açúcar são queimadas. A cana passa por uma queima pré-colheita para facilitar o trabalho dos cortadores e protegê-los, pois elimina do local o excesso de folhas e palhiço e espanta os animais peçonhentos (cobras, escorpiões etc.) muito comuns nas plantações. A queima da cana também melhora o rendimento do corte manual (aumentado em até 10 vezes), auxilia no preparo do terreno para novos plantios e aumenta a quantidade de açúcar por peso, devido à evaporação da água 1,2 . A prática de queimar palha de cana-de-açúcar acarreta problemas de poluição do ar em razão da grande emissão de fumaça e fuligem que podem atingir os centros urbanos, trazendo sérios transtornos à população das cidades canavieiras. A fuligem, que permanece por longo tempo em suspensão no ar, é considerada uma das causas da alta incidência de doenças respiratórias no Brasil 1,4 .As queimadas são consideradas a principal fonte de emissão de material particulado (MP) no mundo. Estima-se que sua contribuição mundial esteja na ordem de 104 Tg/ano 1 . No Brasil, as queimadas de cana-de-açúcar contribuem sem dúvida com emissões de material particulado 1,5 , no entanto, mais est...

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Generalized atomic polar tensor (GAPT) has turned into a very popular charge model since it was proposed three decades ago. During this period, several works aiming to compare different partition schemes have included it among their tested models. Nonetheless, GAPT exhibits a set of unique features that prevent it from being directly comparable to “standard” partition schemes. We take this opportunity to explore some of these features, mainly related to the need of evaluating multiple geometries and the dynamic character of GAPT, and show how to obtain the static and dynamic parts of GAPT from any static charge model in the literature. We also present a conceptual evaluation of charge models that aims to explain, at least partially, why GAPT and quantum theory of atoms in molecules (QTAIM) charges are strongly correlated with one another, even though they seem to be constructed under very different frameworks. Similar to GAPT, infrared charges (also derived from atomic polar tensors of planar molecules) are also shown to provide an improved interpretation if they are described as a combination of static charges and changing atomic dipoles rather than just experimental static atomic charges.

Infrared band intensification of the A–H bond stretching mode of A–H···B acid–base systems has long been known to be the most spectacular spectral change occurring on hydrogen bonding. A QTAIM/CCTDP model is reported here to quantitatively explain the electronic structure origins of intensification and investigate the correlation between experimental enthalpies of formation and infrared hydrogen bond stretching intensifications amply reported in the literature. Augmented correlation-consistent polarized triple-zeta quantum calculations at the MP2 level were performed on complexes with HF and HCl electron acceptors and HF, HCl, NH3, H2O, HCN, acetonitrile, formic acid, acetaldehyde, and formaldehyde electron donor molecules. The A–H stretching band intensities are calculated to be 3 to 40 times larger than their monomer values. Although the acidic hydrogen atomic charge is important for determining the intensities of HF complexes relative to HCl complexes with the same electron donor, they are not important for infrared intensifications occurring on hydrogen bond formation for a series of bases with a common acid. Charge transfers are found to be the most important factor resulting in the intensifications, but dipolar polarization effects are also significant for each series of complexes. A mechanism involving intra-acid and intermolecular electron transfers as well as atomic polarizations is proposed for understanding the intensifications. The calculated sums of the intermolecular electron transfer and acid dipolar polarization contributions to the dipole moment derivatives for each series of complexes are highly correlated with their enthalpies of formation and H-bond intensifications. This could be related to increasing electron transfer from base to acid that correlates with the calculated hydrogen bonding energies and may be a consequence of the A–H bond elongation on complex formation having amplitudes similar to those expected for the A–H vibration.

Infrared gas phase intensities are reported for the first time for 23 CH out-of-plane bending vibrations of eight substituted benzene molecules and naphthalene by integration of bands from the Pacific Northwest National Laboratory (PNNL) spectral library. These experimental values are found to have an rms difference of 8.7 km mol–1 with the B3LYP/6-311++G­(d,p) values for intensities ranging from close to zero to 126.7 km mol–1. These intensities are found to have transferable electronic structure parameters, and their square roots are proportional to the amplitudes of the hydrogen atom displacements perpendicular to the benzene ring. Quantum Theory of Atom in Molecules (QTAIM)–Charge–Charge Transfer–Dipolar Polarization models were determined from the B3LYP/6-311++G­(d,p) electronic densities. By far, the largest electronic contribution to these intensities is the dipolar polarization of the carbon atom of the displaced CH bond, 0.214e. Smaller contributions are found for the polarizations of the displaced hydrogen atoms (−0.043e) and nearest neighbor carbon atoms (−0.052e), both having directions opposite to that of the carbon atom polarization of the displaced CH bond. The movements of static equilibrium hydrogen charges make the smallest contribution canceling most of the hydrogen polarization changes. In fact, the carbon atomic polarizations alone account for 96.9% of the dipole moment derivative vector norm for the CH out-of-plane bends. The polarization model is also found to be valid for seven CH out-of-plane bending vibrations of N-fused benzene ring molecules (N = 3, 4, 5).