A new analytical method has been developed for the determination of inorganic species or arsenic (arsenite and arsenate); in addition, a new sample preparation method for the determination of these species in atmospheric particulate matter has also been developed. In this procedure, As(III) and As(V) are efficiently separated in a two-step reduction procedure from a solution of HCl. In the first step, a slurry of Zn metal powder is used to reduce As(III) to arsine (AsH₃). Immediately following, NaBH₄ is used to reduce As(V) to AsH₃. The arsine produced during each reduction is detected in an N₂-H₂ air-entrained flame by atomic absorption spectroscopy. In the sample preparation method, sections of quartz or PTFE filters containing atmospheric particulate matter are leached in 10⁻⁴ N HCl for up to 1 hour at 90°C. This procedure quantitatively removes As(III) and As(V) from either filter type. However, small changes in the As(III)/As(V) ratio i.e., oxidation of As(III) were observed when the arsenic species were leached from quartz filters. Therefore, it appears that PTFE would be the preferred filter medium if arsenic speciation is to be performed. When atmospheric particles are present on either filter type, the technique of standard addition is necessary in order to obtain the most accurate results. The combined sample preparation and analysis procedure has a precision of about 10%, 8% and 13% for As(III), As(V) and the As(III)/As(V) ratio, respectively. Atmospheric particulate matter samples collected in Tucson, Arizona, were analyzed for As(III) and As(V) concentrations using the newly developed method. The results of this study indicate that both As(III) and As(V) are present in collected samples of atmospheric particulate matter. Arsenic (V) was observed in all 14 of the samples, while As(III) was measurable in half of the samples. The As(III)/As(V) ratio was determined to be in the range from less than 0.05 to 1. An atmospheric detection limit for either species of 0.09 ng m⁻³ was obtained.