The Global Reactive Carbon Budget of the Troposphere

Abstract:

Reactive carbon plays a key role in driving the oxidative chemistry of the atmosphere and is a precursor to ozone and particulate matter formation, both of which impact human health and climate. However, uncertainties on the lifecycle of reactive carbon in the atmosphere remain large. In part this can be attributed to the chemical complexity and variety of species reactive carbon in the atmosphere, and the resulting lack of mass closure in both ambient measurements and models.

In this study we investigate how the reactive carbon budget is represented in a global model, GEOS_Chem, and provide some initial comparisons with observations. We examine the simulated spatiotemporal distribution of the primary and secondary gas and particle phase organic tracers and assess the total organic carbon burden, its vertical distribution and seasonal variation. We use the model sources, sinks, and burden to construct a budget for reactive carbon which we discuss using three properties for categorization: chemical composition, volatility and reactivity.

Since the representation of wet deposition and cloud chemistry differs widely in global models leading to large uncertainties, we also focus our analysis on the wet scavenging of soluble organic species within GEOS-Chem. We compare our simulation with compilations of observed reactive carbon from a series of surface and airborne field campaigns. Finally, we discuss possible modeling improvements for assessing and testing the representation of the reactive carbon budget.