Indications of photochemical histories of Pacific air masses from measurements of atmospheric trace species at Point Arena, California

Abstract

Measurements of light hydrocarbons, ozone, peroxyacetyl nitrate (PAN), HNO3, NO3−, NOx, NOy, and meteorological parameters were made during a 10‐day period in April and May 1985 at Point Arena, a coastal inflow site on the Pacific Ocean in northern California. The meteorological measurements indicate that during this study the sampled air was usually from the marine boundary layer with little land influence on the meteorological parameters. In this marine air the mixing ratios of the alkanes, ozone, PAN, and HNO3 showed strong correlations coincident with variations in the origins of calculated air parcel trajectories and with variations in the ratios of the light alkanes. This variation in the ratios is attributed to different degrees of photochemical aging of the alkanes that are generally consistent with the calculated trajectories. This behavior indicates that the alkane levels are determined by transport to the marine area from continental sources, most likely Asian, followed by photochemical removal over the Pacific Ocean. Since the concentrations of PAN and ozone correlate well with the alkane ratios, it is concluded that the observed PAN and ozone were dominated by continental sources and removal processes in the marine areas. This and other marine studies have observed a strong correlation of PAN and ozone, and it is suggested that production over the continents, transport to the marine areas, and parallel removal processes account for much of the observed correlation. From the correlation of these two species with the measured alkane ratios, approximate net lifetimes of PAN and ozone in the marine troposphere of ≤2.5 and ≥19 days, respectively, are derived. The primary conclusion is that the alkanes, ozone, and PAN in these air parcels from the Pacific marine troposphere are dominated by transport from continental sources and removal by photochemical processes. Direct emissions of the alkanes and in situ photochemical production of PAN and ozone from precursors emitted into the marine region from the surface or the stratosphere must play less important roles. Similar indications of continental influence in marine areas have been seen in other studies of ozone, the sulfur cycle, oxidized nitrogen, and hydrocarbons. It is suggested that the ratios of the light alkanes provide photochemical “clocks” that are useful for gauging the importance of continental influence in a particular marine measurement.

Changes in the photochemical environment of the temperate North Pacific troposphere in response to increased Asian emissions

“…The 1985 study represent the only relatively early measurements, but fortunately two, wellrespected measurement groups simultaneously measured PAN, and the results agreed well [Parrish et al, 1992].…”

“…These minimum O 3 levels are observed in highly aged air masses, which are those that have resided for long periods in the North Pacific troposphere. In 1985 the higher O 3 levels were observed only in relatively fresh air masses that had been rapidly transported across the Pacific [Parrish et al, 1992]; these higher O 3 levels have not changed as significantly in the intervening years. Tests of this interpretation constitute the remainder of this section.…”

“…[9] Experimental details regarding the various PAN data sets are reported by Parrish et al [1992], Jaffe et al [2001], Kotchenruther et al [2001a], and Roberts et al [2004], who estimated accuracies from 15 to 30% depending upon the study and the PAN levels. The 1985 study represent the only relatively early measurements, but fortunately two, wellrespected measurement groups simultaneously measured PAN, and the results agreed well [Parrish et al, 1992].…”

“…A more extensive data record of NO x measurements is lacking. The two early 1984 and 1985 field studies [Chameides et al, 1989;Parrish et al, 1992] cannot define NO x levels in those years. The 1984 data are very limited and NO 2 was not measured.…”

“…In Figure 3a the linear least squares fits to the 5th percentiles, the means, and the 95th percentiles are plotted, and in Figure 3b similar lines connect the corresponding parameters for the two aircraft campaigns. [22] Parrish et al [1992] use the relationship between O 3 and hydrocarbon aging patterns to evaluate the sign and qualitatively estimate the magnitude of P(O 3 ). They focused on the photochemical processing of MBL air masses sampled during the spring 1985 Point Arena study.…”