New England Air Quality Study

Atmospheric concentrations of ozone and particulate matter (PM) over southern New England often exceed established air quality standards. Although substantial progress has been made in understanding the sources and processing of these air pollutants, significant knowledge gaps in key areas still remain, particularly in coastal regions. Ozone and fine particles are both formed and removed through complex series of atmospheric chemical reactions. Their precursors are emitted from both natural and anthropogenic sources, often far away and hence involving transport over long distances. Transformations and removal involve a crucial but poorly understood subset of chemical reactions that are multiphase, i.e., involving gas-aerosol interactions, many of which depend strongly on the acidity (pH) of the particles. For example, the partitioning of nitric acid, the principal end product of gas phase odd nitrogen chemistry, into coarse aerosols and the subsequent removal of the aerosols by deposition to the Earth’s surface is the dominant sink for the key ozone precursor NOX (NO + NO2).

During July and August 2002, AIRMAP in collaboration with several NOAA laboratories conducted an intensive field campaign called the New England Air Quality Study (NEAQS) 2002 focusing on the transport and transformation of nitrogen oxides, ozone, and sulfur compounds over the New Hampshire seacoast and adjacent waters. A broad suite of air chemistry and meteorological measurements ere made aboard NOAA Ship Ronald H. Brown during a cruise dedicated to this intensive. The Observatory teamed up with UNH and the University of Virginia to augment the planned “core” chemical measurement suite and obtain data with which to address the following objectives:

  • To constrain by “closure” the pH of Gulf of Maine boundary layer (GoMBL) aerosols as functions of particle size, meteorological conditions, and chemical regime.
  • To assess the significance of pH-dependent, gas-particle interactions with respect to the cycling of odd nitrogen, sulfur and other chemical species in the GoMBL.

Size-segregated aerosols were sampled with cascade impactors and analyzed for major ionic constituents. The pH of minimally diluted extracts of these samples were measured and extrapolated to ambient conditions using hygroscopicity models. Nitric, hydrochloric, formic and acetic acids, ammonia and sulfur dioxide were quantified in parallel with a tandem-mist-chamber technique. Aerosol pHs as a function of size were inferred independently from the measured phase partitioning of the gases and associated thermodynamic properties, and were compared with those estimated from direct pH measurements to assess “closure”. The principal results of this work have been published by Keene et al. [2004]. The data generated by the UNH/MWO/UVA group were also used by de Gouw et al. [2003] to validate acetic acid measurements by Proton Transfer Reaction Mass Spectrometery (PTR-MS) and by de Gouw et al. [2005] to develop an organic carbon budget for the polluted coastal New England atmosphere.