Observations of ozone and related species in the northeast Pacific during the PHOBEA campaigns: 2. Airborne observations

Robert A Kotchenruther,Harald J Beine,Joyce M Harris,Rainer Schmitt,Theodore L Anderson,Donald R Blake,Jan W Bottenheim,Daniel A Jaffe

doi:10.1029/2000jd900425

Abstract

During late March and April of 1999 the University of Wyoming's King Air research aircraft measured atmospheric concentrations of NO, O3, peroxyacetyl nitrate (PAN), CO, CH4, VOCs, aerosols, and J(NO2) off the west coast of the United States. During 14 flights, measurements were made between 39°–48°N latitude, 125°–129°W longitude, and at altitudes from 0–8 km. These flights were part of the Photochemical Ozone Budget of the Eastern North Pacific Atmosphere (PHOBEA) experiment, which included both ground‐based and airborne measurements. Flights were scheduled when meteorological conditions minimized the impact of local pollution sources. The resulting measurements were segregated by air mass source region as indicated by back isentropic trajectory analysis. The chemical composition of marine air masses whose 5‐day back isentropic trajectories originated north of 40°N latitude or west of 180°W longitude (WNW) differed significantly from marine air masses whose 5‐day back isentropic trajectories originated south of 40°N latitude and east of 180°W longitude (SW). Trajectory and chemical analyses indicated that the majority of all encountered air masses, both WNW and SW, likely originated from the north‐western Pacific and have characteristics of emissions from the East Asian continental region. However, air masses with WNW back trajectories contained higher mixing ratios of NO, NOx, O3, PAN, CO, CH4, various VOC pollution tracers, and aerosol number concentration, compared to those air masses with SW back trajectories. Calculations of air mass age using two separate methods, photochemical and back trajectory, are consistent with transport from the northwestern Pacific in 8–10 days for air masses with WNW back trajectories and 16–20 days for air masses with SW back trajectories. Correlations, trajectory analysis, and comparisons with measurements made in the northwestern Pacific during NASA's Pacific Exploritory Mission‐West Phase B (PEM‐West B) experiment in 1994 are used to investigate the data. These analyses provide evidence that anthropogenically influenced air masses from the northwestern Pacific affect the overall chemical composition of the northeastern Pacific troposphere.

Highlights

The East Asian region is a large and growingsourceof anthropogenicemissions[Akimotoand Narita, 1994; Elliott et al, 1997;VanAardeenet al., 1999]
Chemicaltransportmodel to determinethe impact of Asian industrialemissionson air arriving to North America
Experiment model calculationsestimatedthat 10, 20, and 30% of the 03, CO, and peroxyacetylnitrate (PAN), respectively,in air arriving to North America during spring resultedfrom Asian industrial emissions

Summary

Data Analysis and Discussion

Air Mass Trajectory Analysis sourceregion as determinedfrom 5-day back isentropictrajectories. The categorieswere (1) continentalNorth America: Back isentropictrajectorieswere calculatedto determine those that crossed over the North American continent within 3 the sourceregionsfor air massesencountereduringaircraft days,(2) westerlyandnorthwesterly(WNW): thosetrajectosampling. Only 1200 UT and0000 UT traandNOAA's Air ResourcesLaboratory(ARL) usingtheHy- jectory starting times were available from NOAA CMDL. Brid Single-Particle Lagrangian Integrated Trajectory Thereforeboth the 1200 UT and 0000 UT back trajectories (HYSPLIT4) model, 1997 (http://www.arl.noaa.gov/ready/bracketingthemeasuremenwt ereusedto classifythe air mass hysplit4.html) with the National Center for Environmental sourceregion. Trajectoriesof 10 day durationwere availablefrom back trajectoryfrom NOAA ARL was usedto "break the tie". NOAA CMDL startingevery hours,andthoseof 5 daydu- and classifythe sourceregion. The resultingclassifications ration were availablefrom NOAA ARL startingevery hour. Thesedata indicatethat the WNW regionis generally twice as likely to be influenced by 5 day old air from these cities

Data Quality Control to Remove Local Pollution

Comparing WNW With SW Data

Comparingthe RelativePhotochemicaAl geof Air MassesWith Their Trajectory Age

Findings

NO2 and NOx