Atmospheric deposition chemistry in a Brazilian rural area: alkaline species behavior and agricultural inputs

Abstract

Since 2000s, several studies have been reporting an increase of alkaline species in atmospheric deposition worldwide. This study aims to evaluate and give a better understanding about atmospheric deposition chemistry collected in Lavras, a Brazilian city with rural background. Bulk atmospheric deposition samples were collected from March 2018 to February 2019 and major ionic species were quantified. The pH values ranged from 5.52 to 8.29, with an average of 5.92 and most deposition samples (~ 94%) were alkaline (pH > 5.60). For the whole sampling campaign, the ions profile in volume weighted mean (VWM) was described as follows: Ca2+ (35.02) > NH4+ (11.26) > Cl− (11.19) > Mg2+ (9.04) > NO3− (8.57) > Na+ (5.65) > K+ (2.61) > SO42− (2.43) > H+ (0.94) μmol L−1. We identified Ca2+ and NH4+ as the most predominant species accounting for 53% of the total ionic species distribution. In addition, all samples showed neutralization factor (NF) index greater than 1, with mean value of 6.4. Regarding regression analysis, acidity neutralization precursors such as calcium and ammonia accounted for 50% and 4%, respectively. In addition, samples alkaline pattern was mainly due to agricultural sources, including fertilizer production and application, and cement manufacturing inside the county air basin.