Exploring the Increasing Trend of Organic Carbon in the Atmospheric Aqueous Phase in the Northeast U.S.

Christopher Lawrence1, *, Sara Lance1, Eric Apel2, Rebecca Hornbrook2, Georgia Murray3, Desneiges Murray4, Adam Wymore4, Bill McDowell4, James Shanley5, Jon Campbell6, Michelle Shattuck4, Paul Casson1, Archana Tripathy1,

and Phil Snyder7

Organic carbon (OC) is a highly diverse class of compounds that represents a small but critical fraction of the atmosphere's chemical composition. Volatile organic compounds (VOCs), when combined with nitrogen oxides (NOx), can produce tropospheric ozone (O3), a regulated air pollutant. OC also represents a large and growing fraction of aerosol mass, either through direct emissions from sources like fossil combustion and biomass burning, or through secondary chemistry by the oxidation and subsequent reduction of vapor pressure of VOCs leading to condensational growth. Clouds droplets and precipitation can contain additional OC due to the dissolution of soluble organic gases to the aqueous phase.

OC has abundantly been found in aqueous samples of clouds, fog, and precipitation, exposing these compounds to unique aqueous chemical reactions and wet deposition. However, the concentrations and controlling factors of atmospheric aqueous organic carbon remain highly unconstrained. Cloud water measurements at Whiteface Mountain in the Adirondack Mountains in upstate New York have revealed an increasing trend of Total Organic Carbon (TOC), with annual median concentrations doubling in 14 years, possibly signalling a growing trend in atmospheric OC. However, the causes and potential consequences of this trend remain unclear. Another question that has yet to be explored is if this trend in OC extends beyond WFM. To answer this question, this work explores the trends of WFM cloud water and 4 additional long-term cloud water and wet deposition datasets that have measured TOC or dissolved OC (DOC) throughout the Northeast US. These sites include Mt Washington, NH, Hubbard Brook NH, Thompson Farm NH, and Sleepers River Vermont. This work will also discuss potential hypotheses driving this increasing trend including increased biomass burning influence and increased biogenic emissions in the region.

1 University at Albany, Albany, NY

2 University Corporation for Atmospheric Research, Boulder, CO

3 Appalachian Mountain Club, NH

4 University of New Hampshire, Durham, NH

5 U.S. Geological Survey, New England Water Science Center, Montpelier, VT

6 USDA Forest Service, Northern Research Station, Durham, NH

7 Ausable Freshwater Center, Wilmington, NY

* Corresponding author: celawrence@albany.edu