Seasonal Observations of Atmospheric Volatile Organic and Sulfide Compounds near a Pulp Paper Mill in North-Central Idaho

Air composition of the Lewis-Clark Valley (LCV) was studied over a two-year period to investigate the effects of a local pulp paper mill on ambient air and to assess potential health risk to the community. Lewiston, Idaho and Clarkston, Washington are twin cities in the Snake River Valley bordering North-Central Idaho and Southeastern Washington, with a population of over 50,000 including the surrounding areas. The paper mill is located in North Lewiston and releases malodorous sulfur air pollutants in the LCV. The neighboring Nez Perce Tribe has conducted a couple of air studies, in 2006-2007 and the summer of 2016-17, but to date no longer term study has taken place. Our current study utilized active air sampling via sorbent tubes followed by thermal desorption gas chromatography-mass spectrometry (TD-GC-MS) analysis to measure over 50 volatile organic compounds, hazardous air pollutants, and sulfides in ambient air (adapted from EPA Method TO-17). Seasonal, diurnal, and spatial variations in air composition were explored. In addition, monthly averaged passive air samples were collected for comparison at nearby urban areas - Boise, ID, Coeur d'Alene, ID, and Spokane, WA in 2018. In the LCV, dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) were the primary sulfur compounds detected, with concentrations highest adjacent to the paper mill. However, concentrations varied considerably depending on time of day, season, location and meteorology. Seasonal observations include DMS, benzene and chloroform peaking in the summer months, while DMDS peaks in the winter. Diurnal trends show DMS and chloroform with higher values during the morning hours than later in the day. The long-term monthly samples show benzene decreasing from winter to spring, with LCV levels comparable to Coeur d'Alene and Spokane, and Boise slightly higher. In most cases, benzene levels exceed those recommended for ambient air in the state of Idaho. Sources and potential health implications will be discussed.