Diurnal/Overnight variation of PM2.5 and PM2.5-10 composition in the dry and wet season of 2008 in Cuiabá City, Mato Grosso State, Brazil

RODRIGO MARQUES (1,2), Adalgiza Fornaro (1), Regina Maura de Miranda (1), Rosana Astolfo (1), Edinaldo de Castro e Silva (3)

(1) Department of Atmospheric Sciences, University of São Paulo (IAG/USP), (2) Secretary of the State for Planning and General Coordination for the State of Mato Grosso (SEPLAN-MT), Cuiabá, (3) Federal University of Mato Grosso, Cuiabá.

     Abstract Number: 370
     Last modified: November 9, 2009

Abstract
Cuiabá City is located in the Mato Grosso State, has about 530 thousands inhabitants and 220 thousands vehicles. Mato Grosso State has been impacted by the agribusiness activities increase in the Brazilians Savannah and Amazon Rainforest. The biomass burning has been used like a principal deforestation method. Cuiabá has a tropical climate with two seasons well definite, being a wet season (October to April) and a dry season (May to September). This work intends to analyze the diurnal/overnight variation of PM2.5, PM2.5-10, black carbon (BC) and chemical composition. Samples were collected in intervals of 12h, in the period of January 20 to February 2, July 10 to 23, and September 16 to 29 of 2008. The sampling periods represent wet season, and dry season with different characteristics, biomass burning activities were more intensive in September than July. Dichotomous Sampler 241 (Andersen/ Graseby) was used with air flux of 16.7 litres per minute, calibrated using Sierra’s Top Track flux meters. These samples were analyzed by gravimetry for mass concentration and optical reflectance for Black carbon concentration, and chemicals have been measured by ionic chromatography and X-ray fluorescence. Results by NOAA-15 sensor showed in the Mato Grosso State 21 biomass burning areas in January, 1,688 in July, and 5,655 in September. Diurnal variation of PM2.5 (in micrograms per cubic meters) was 7 (January) and 51 (September), and overnight variation was 7 (January) and 76 (September). For PM2.5-10 diurnal variation was 8 (January) and 68 (July), and overnight variation was 10 (January) and 126 (September). Black Carbon of diurnal PM2.5 and PM2.5-10 concentrations (in micrograms per cubic meters) had variation of 0.3 and 5.7 and 0.03 to 1.2, respectively. And BC overnight variation of PM2.5 and PM2.5-10 was 0.6 to 9.5, and 0.05 to 2.6, respectively. In these samples, BC represented 32% of PM2.5 mass and only 3% of PM2.5-10 mass. Mass balance for chemical composition has indicated the soil as main source to PM2.5-10, with important contribution of limestone mining and cement plants. For PM2.5, biomass burning was the main source, following by secondary process. It is important to emphasize that overnight concentrations were higher than diurnal, mainly during dry season, when thermal inversion was more intense and usual, associated with biomass burning and low wind speed. Other influence was the distribution of precipitation, raining 314 mm in January, 4 mm in July and 21 mm in September.