Aerosol acidity in rural New England: Temporal trends and source region analysis

Data from 24‐hour bulk filter samples collected by the AIRMAP program were used to estimate aerosol acidity at a site in New England. The sampling site, Thompson Farm in Durham, New Hampshire, is situated 15 km inland from the Atlantic Ocean. The aerosol chemical composition in this area is dominated by sulfate (SO 4 2− ) and ammonium (NH 4 + ) and aerosols that are weakly acidic, most likely because of a lack of regional sources of gaseous ammonia (NH 3 ). Nitrate (NO 3 − ) plays a smaller role in aerosol acidity. The median SO 4 2− aerosol concentration was highest during the summer (23.7 nmol m −3 ). Inferred fine NO 3 − concentrations were highest in the winter, with a median concentration of 0.2 nmol m −3 . Increased inferred hydrogen ion concentrations and the least neutralized aerosols are associated most strongly with coastal sources, potentially because of smaller NH 3 sources relative to sulfur sources in these regions. During the International Consortium for Atmospheric Research on Transport and Transformation (ICARTT) campaign during summer 2004, the composition of fine aerosol was dominated by SO 4 2− , NH 4 + , and organics. Acidic aerosols sampled during this campaign were largely anthropogenic in origin and photochemically aged.