Association between ionic composition of fine and coarse aerosol soluble fraction and peak expiratory flow of asthmatic patients in São Paulo city (Brazil)

Air pollutants are associated with adverse respiratory effects mainly in susceptible groups. This study was designed to assess the impact of the ionic composition of particulate matter on asthmatic respiratory functions in São Paulo city. From May to July 2002, fine and coarse particulate matter fractions were collected and their respective chemical composition with respect to major ions (Na+, Mg2+, K+, Ca2+, NH4+, Cl−, NO3− and SO42−) were determined in each aqueous-extract fraction. The results showed predominant concentrations of SO42− (48.4%), NO3− (19.6%) and NH4+ (12.5%) in the fine fraction, whereas NO3− (35.3%), SO42− (29.1%), Ca2+ (13.1%) and Cl− (12.5%) were the predominant species in the coarse fraction. The association between the chemical components of both fractions and the daily peak expiratory flow (PEF) measurements (morning and evening) of the 33 asthmatic individuals were assessed through a linear mixed-effects model. The results showed a significant negative correlation (decrease of PEF) between morning PEF and coarse chloride (3-day moving average) and between evening PEF and coarse Na+ (3-day moving average), coarse Mg2+ (3-day moving average) and coarse NH4+ (2- and 3-day moving average). A significant negative correlation has also been observed between morning and evening PEF and Mg2+ in the fine fraction. These results suggest that some particle chemical constituents may increase the responsiveness of airways and that coarse particles that deposit in the upper airways may be more relevant for asthmatic response and irritation. However, the results do not prove a clear causal relationship.