Organic components in bulk and wet‐only precipitation

Atmospheric pressure mass spectrometry: a new analytical chemical characterization method for dissolved organic matter in rainwater

The complex mixture of organic compounds in the atmosphere influences climate, air quality, and ecosystem processes. Atmospheric pressure electrospray ionization mass spectrometry (APESI-MS) was evaluated as a potential tool for direct measurement of the total suite of individual dissolved organic matter (DOM) compounds in rainwater. The APESI-MS response was linear to all DOM compounds of atmospheric significance examined as standard solutions. Urban precipitation samples from New Brunswick, NJ (USA) were analyzed by APESI-MS over the mass-to-charge (m/z) range 50-3,000. Over 95% of the m/z ions detected were in the low m/z range (50-500). Over 300 unique m/z ions were detected across the 11 rainwater samples indicating the complexity of the mixture of DOM in rainwater. Forty percent of the organic bases (positive mode detection) and 22% of the organic acids (negative mode) occurred in at least 6 of the 11 rainwater samples. Ions corresponding to the m/z of carboxylic acids standards (nonanedioic acid; 1,4-butanedicarboxylic acid; pentanedioic acid; hydroxybutanedioic acid; and butanedioic acid) and to reduced N standards (allylurea; caffeine; imidazole; and N-2-propenylurea) occurred in at least one of the 11 rainwater samples. Total dissolved organic carbon (DOC) estimated from the APESI-MS analysis and measured by standard DOC methods were not statistically different.

Organic aerosols in the Miami area, USA: temporal variability of atmospheric particles and wet/dry deposition

Atmospheric particulate matter and both wet and dry deposition was collected over a period of nine months at one location in the metropolitan area of Miami, Florida. Molecular distributions and concentrations of n-alkanes, fatty acids, polycyclic aromatic hydrocarbons (PAHs) and hopanes were determined using weekly composite samples over this time period in order to determine temporal variability, and their possible dependence on climatic parameters such as temperature, rainfall and wind direction and frequency. Based on molecular distributions of the compounds studied, potential emission sources for the atmospheric particles were assessed and suggested to be mainly derived from automobile exhaust and natural sources. Although wet and dry deposition processes were observed to remove about equal amounts of organic aerosols from the Miami atmosphere, dry deposition was dominant in the removal of anthropogenically derived compounds such as PAHs and hopanes. Only very limited seasonal trends were observed, while wind direction and frequency was found to be the most important meteorological parameter controlling the temporal variability of the organic aerosols. This is the first detailed report of this nature for the Miami area.