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Amostras de MP2,5 e MP2,5-10 foram coletadas em São José dos Campos (São Paulo) de fevereiro de 2004 a fevereiro de 2005. Nesse período ocorreram duas longas estiagens, com durações de 25 e 38 dias consecutivos. As concentrações de MP foram maiores na segunda do que na primeira. Os dados foram divididos em dois grupos, um contendo resultados das medições efetuadas durante as duas estiagens (período seco) e outro contendo os dados do restante do ano (período regular). As concentrações médias do MP2,5 e MP2,5-10 foram respectivamente 23 ± 7,5 µg m-3 e 19 ± 7,9 µg m-3 no período seco e 14±7,9 µg m-3 e 13 ± 7,9 µg m-3 no período regular. Houve variação entre os dias da semana, com concentrações médias de MP maiores na quarta-feira (MP2,5) e quinta-feira (MP2,5-10) e menores no domingo. A variação mais acentuada ocorreu para o MP2,5-10, sugerindo uma relação com emissões veiculares. Durante os períodos seco e regular, as concentrações de SO4(2-) e NH4+ foram aproximadamente 5 vezes maiores no MP2,5 do que no MP2,5-10. No MP2,5, as concentrações iônicas foram maiores no período seco (exceto Cl-, Na+ e Mg2+), especialmente K+. Análise de agrupamentos e trajetórias reversas de massas de ar para o MP2,5 sugere influência continental de origem significativa para os íons NO3-, SO4(2-), NH4+ e K+. PM2,5 and PM2,5-10 samples were collected at São José dos Campos (São Paulo) from February 2004 to February 2005. During this time there were two periods of drought, one lasting for 25 consecutive days and a second one for 38 days. The later exhibited higher PM concentrations values than the first one. Data were divided into two groups, one comprising all measurements carried out during the 63 days without rain (dry period) and a second one comprising the remaining data (regular period). The PM2,5 and PM2,5-10 average concentrations were respectively 23 ± 7.5 and 19 ± 7.9 µg m-3 during dry period and 14 ± 7.9 and 13 ± 7.9 µg m-3 during regular period. There was a day-of-week variation with highest average concentrations on Wednesday (PM2.5) and Thursday (PM2.5-10) and lowest on Sunday. The PM2,5-10 exhibited the most pronounced variation suggesting an association with vehicular emissions. During both dry and regular periods, average SO4-2 and NH4+ concentrations were about 5 times higher in the fine than in the coarse fraction. PM2,5 ionic concentrations, especially that of K+, were higher in the dry period compared to regular one (except for Cl-, Na+ and Mg2+). Hierarchical cluster analysis and backward air mass trajectories indicate that during the dry period NO3-, SO4(2-), NH4+ and K+ associated with PM2.5 are significantly influenced by continental sources.

Air samples of fine (PM2,5) and coarse (PM2,5-10) particulate matter were collected in São José dos Campos from February 2004 to February 2005. Average PM10 mass concentrations was 31.2 ± 14.0 μg m-3, half of which belonging to the PM2.5 fraction. Ammonium and SO4(2-) were predominantly found in the fine fraction. Average (NH4)2SO4 concentration was estimated to be about 2.9 μg m-3. Chloride, Na+ and NO3- were mostly associated with PM2,5-10. Chloride deficits with respect to sea-salt Cl/Na ratio were found in both size fractions.