Chemical composition of rainwater under two events of aerosol transport: A Saharan dust outbreak and wildfires.

A one-year campaign of joint sampling of aerosols and precipitation, carried out in León, Spain, allowed to study the impact of two special events that affected the air quality in the north of the country, on rainfall in the city: a period with wildfires and a Saharan dust intrusion. The wildfires that occurred in northern Portugal and northwestern Spain in August 2016 affected the chemistry of rainfall on 15 August 2016, causing an increase in concentrations of NH, Na, Cl, K, Mg, Ca, SO and NO and in the concentrations of organic acids, which was reflected in the levels of soluble and insoluble organic carbon. This led to acidification of rainwater (pH = 4.8). The second precipitation event was registered between 11 and 14 February 2017, during which the rainwater was collected in four daily fractions (P, P, P and P). The rain sample of 12 February (P) coincided with a Saharan dust intrusion that reached northern Iberia that day. The chemical composition of P showed an increase in the Ca (>800%), Mg (71%), Cl (62%), and SO (33%) concentrations, with respect to P. The input of crustal elements to the atmosphere helped to neutralize the P rainwater, causing pH values higher than 6.5. Once the dust intrusion left the north of the Peninsula, the composition of rainwater P and P revealed a mixture of marine contribution with local anthropogenic emissions, as well as a decrease in ion concentrations and conductivity, and an increase in pH values.