Caracterização química do aerossol submicrométrico em Chacaltaya, Bolívia

Abstract

The aerosol consists of a mixture of solid and liquid particles suspended in the air, subject to size variation as a result of physical and chemical processes occurring in the atmosphere and with importance for atmospheric dynamics, as they influence the climate and affect human health. The aim of this research was to chemically characterize the submicrometric aerosol for one year (April/2018 to March/2019) into three periods: dry season (May to August/2018), wet season (December/2018 to March/2019) and transition period (April and September to November/2018) and to identify the main chemical classes of aerosols and organic components at observation site in Chacaltaya (CHC), Bolivia. CHC is located 30 km from La Paz, the country’s capital, at 5240 m a.s.l. in the Andes Moutain. In order to better understand the aerosols properties, the Quadrupole Aerosol Chemical Speciation Monitor (Q-ACSM) was used to characterize its non-refractory fraction and the Multi-Angle Absorption Photometer (MAAP) detected the concentration of black carbon (BC). On average, the aerosol was composed of 41% organics, 32% sulfate, 10% ammonium, 9% BC, 8% nitrate and less than 1% chloride. The diurnal profile of the compounds shows an increase in concentration around 10am (local time) due to the development of the planetary boundary layer (PBL) and the arrival of air mass with pollutants from La Paz and El Alto in CHC. The nitrate and chloride species were identified during the arrival of these air masses and could possibly be used as air pollution tracers for these sources. Five factors were identified in the organic aerosol (OA) by the Positive Matrix Factorization (PMF), four of them being present in the three periods: oxygenated OA (OOA), isoprene derived epoxydiol-secondary OA (IEPOX-SOA), with the presence of hydrocarbons (HOA) and volcanic-related OA (VOOA) and only in the dry season the biomass burning OA (BBOA) was identified. OOA was the dominant factor in the dry, wet and transition 47, 37 e 51%, respectively. The presence of IEPOX-SOA factor suggests that aerossols derived from isoprene have been transported oven long distances, possibly from the lowlands of Bolivia and Brazil. The identification of VOOA aerosol factor for the first time, suggests the presence of organosulfates in the aerosol present in CHC station.