Wet-only sequential deposition in a rural area in north-eastern Spain

The present work summarises the results of a 2-year study of wet-only seque ntial deposition in 2 rural areas (Alcaniz and Morella) located at differen t distances from a large coal-fired power station. Precipitation chemistry Has characterised by relatively high SO42, Ca2+ and NH4+ average concentrat ions. Sequential study of single precipitation events showed that concentra tions of most of the ions studied decreased exponentially throughout single precipitation events. with a sharper decrease in concentrations at the beg inning of the event. Usually. 40 to 80% of the wet-only deposition of major ions occurred in the first 2 mm. pll measurements, ranging from 5.6 to 8.1 , showed a decrease in the pH values throughout a precipitation event. Depo sition levels of Ca2+ I and NH; accounted for the neutralisation of major a cidic species in the precipitation events except in 5 rain episodes sampled at Morella. The sequential study of the evolution of the (SO42- + NO3-)/(C a2+ + NH4+) ratio during a single precipitation allowed us to identify pote ntial acidic rainfall fractions after an initial volume of precipitation. a fter most of the Ca2+ in atmospheric particles had been scavenged. A higher neutralisation capacity was deduced for Alcaniz owing to the higher atmosp heric levels of natural carbonates and NH4+.