Spatiotemporal Variability of Trace Gases in the San Joaquin Valley during DISCOVER-AQ.

Abstract:

Near-surface abundance of trace gas species can exhibit complex horizontal and vertical structures, which may present challenges for satellite based observation or model sub-grid parameterization. Even long-lived species, which are often modeled as globally well mixed, have been observed to contain significant regional and local anomalies from the global seasonal background. The vertical profile of these anomalies is critical in deriving surface and column distributions from remote sensing retrievals. Complex emissions patterns both in time and space present a major challenge in characterizing regional scale concentrations. Vertical mixing, and local wind circulation, which can be strongly modulated on diurnal time scales, contribute to the relationship between column and surface abundances and the horizontal scales of variability.

The San Joaquin Valley (SJV) contains a complex mix of surface emissions including urban, agricultural, oil and gas exploration and processing, and major highways. In addition, the ventilation of the SJV is highly variable and periods of stagnation can exist for several days. During the campaign, two such stagnation periods were observed, interrupted by the passage of Pacific mid-latitude systems. We present results showing the relationship between emissions, regional meteorology and chemistry in explaining the modes of variability observed in key trace gas species including carbon dioxide, carbon monoxide, odd nitrogen, ammonia and methane.