Trace gas composition of midlatitude cyclones over the western North Atlantic Ocean: A conceptual model

Abstract

Midlatitude cyclones provide the energy necessary for most of the trace gas transport from North America to the western North Atlantic Ocean (WNAO). These cyclones are composed of four primary airstreams: warm conveyor belt (WCB), cold conveyor belt (CCB), dry airstream (DA), and post cold front (PCF) airstream. This study is the first to present a conceptual model of the chemical composition of a midlatitude cyclone tracking from North America to the WNAO. The model, a composite of chemical measurements from several cyclones, establishes the fundamental relationships between large-scale chemical transport and midlatitude cyclone structure. It also separates the meteorological influences on airstream trace gas signatures from the influence of surface emissions heterogeneity and presents characteristic mixing ratios of ozone, CO, NOx, and NOy within the four types of airstream during late summer/early autumn. While cyclone track and surface emissions heterogeneity impact the median trace gas values within airstreams, the O3/CO and O3/NOy slopes remain fairly constant. Several characteristics of the conceptual model impact trace gas signatures, regardless of cyclone track: (1) the DA always advects stratospheric ozone into the middle and upper troposphere; (2) the WCB is a more favorable location for photochemical ozone production than the CCB or PCF; (3) the PCF originates to the northwest, is unaffected by wet deposition, and the sunny conditions may allow for some photochemical ozone production; (4) the CCB is generally cloudy and does not show signs of significant photochemical ozone production; (5) both the CCB and the WCB experience wet deposition resulting in little NOy export from the lower troposphere.