Contribution of chemical composition to oxidative potential of atmospheric particles at a rural and an urban site in the Po Valley: Influence of high ammonia agriculture emissions

Abstract

The present study investigates the chemical composition and oxidative potential (OP) of PM10 particles at two sites in the Po Valley (Norther Italy), with the aim of evidence the impact of high level of atmosphere ammonia (NH3). Field measurements were conducted in a rural location (Bertonico) close to farms strongly impacted by high ammonia emissions from agriculture and livestock husbandry. The urban site was in the metropolitan area of Milan. The NH3 concentrations observed at the rural site were about 5 times higher than those at the urban location, generating higher levels of secondary inorganic aerosol (ΣSIA) at Bertonico (16.6 ± 6.33 μg m−3) than at Milan 12.6 ± 4.93 μg m−3. The oxidative potential measured with the ascorbic acid assay (OPAAV) was almost triple in Milan than at Bertonico, namely 1.48 ± 1.08 nmol min−1 m−3 and 0.44 ± 0.23 nmol min−1 m−3, respectively, while the measured OPDTTV responses were similar at both sites, close to ∼ 0.5 ± 0.3 nmol min−1 m−3. These results suggested that the SIA components don't significantly contribute to the PM10 oxidative reactivity, although they account for most of the PM10 mass. Despite such an OP-inactivity, the SIA components resulted significantly correlated with both OPAAV and OPDTTV responses. This may be likely due to their inter-correlation with other redox-active components, such as the secondary organic species, which are synergically produced along with the SIA formation. In addition, an increase in the metals reactivity towards the OP assays, may be associated with the PM10 acidic environment produced by enhanced HNO3 and H2SO4 levels. Therefore, the contribution of the SIA to PM oxidative toxicity cannot be ignored in assessing health risk associated with PM exposure.