|Large enhancements in PAN, ozone, and other chemical species (not shown) were observed during a large pollution event on April 23rd (Day 113). Also shown in this plot is "Hours in the Asian Box," a trajectory-derived parameter that provides an estimate of the probability that air has been influenced by the continental boundary layer of central East Asia.|
Mount Bachelor Observatory (MBO) is located on the summit of Mount Bachelor, a dormant volcano in the Cascades of central Oregon. The site is maintained primarily by the Jaffe group at UW Bothell and Mt. Bachelor, Inc. ski area. At 2.7 km (9000 ft) above sea level, the research station regularly receives free tropospheric air, making it an ideal location for studying a number of intriguing chemical/meteorological phenomena, particularly long range transport of asian pollution.
Recent research efforts by groups at Mount Bachelor and other sites, in addition to several airplane-based field campaigns and extensive satellite imaging, have revealed a significant influx of asian pollution plumes to the Pacific Northwest. Such plumes are particularly prevalent during the springtime, when trans-Pacific transport events are observed to be strongest and free radical-induced photochemical ozone production is at its peak. This pollution, as well as the ozone generated during transport and subsidence, may have important consequences for air quality in western North America, particularly in rural and remote regions where sources of ozone precursors are minimal.
2006 MBO FIELD INTENSIVE
To further characterize the nature of transported asian pollution and its effects on tropospheric ozone production in the Pacific Northwest, we are currently involved in a collaborative field campaign with several other groups at Mount Bachelor, including the Jaffe group (UW Bothell), the Simonich group (Oregon State University) and the University of Michigan Air Quality Laboratory. Measurements made at Mount Bachelor during the intensive (from April to May) included wind speed and direction, temperature, RH, ozone, CO, acyl peroxy nitrates (APNs), NO/NOy, NO/NOx, Hg (gaseous, particulate and elemental), radon, aerosol scattering, semi-volatile organic compounds and PM 2.5 concentrations. The MBO field intensive was also run jointly with NASA's INTEX-B campaign, thus allowing for measurement intercomparisons and providing a more complete data set with which we may begin to assess the impact of asian pollution on ozone production chemistry at MBO.With funding from the NSF and NASA*, we deployed our CIMS to Mount Bachelor to make measurements of a range of acyl peroxy nitrates, including PAN, PPN, PiBN/PnBN, MPAN and APAN. This particular class of compounds are known to act as chemical vehicles in the long-range transport of NOx across the Pacific and can also provide information on pollution sources (e.g. biomass burning, fossil fuel combustion, etc).
The above figure shows time traces of peroxyacetyl nitrate (PAN), peroxypropionyl nitrate (PPN), the ratio of PPN to PAN and ozone measured from April 11 to May 14, 2006 (for reference, day 100 is April 10th). APN mixing ratios varied by orders of magnitude throughout the month and are highly event-driven. PPN/PAN, often used as an indicator for anthropogenic influence, shows that much of the air reaching MBO has been influenced to some degree by anthropogenic hydrocarbons but is also photochemically well-aged. Changes in ozone are often correlated with changes in PAN, especially during pollution episodes (c.f. days 129 and 132). Combining this data with other available measurements and back trajectory analysis, we have been able to gain insight into the origin of these air masses and their effects on ozone production chemistry. The figures below illustrate some of our preliminary findings.
|HYSPLIT back trajectories for the
pollution episode shown at the left indicate that a strong Asian
transport event was observed at this time. ~5 days prior to arriving at
MBO, air from the Asian continent was rapidly lofted to the free
troposphere, where westerly winds carried it to North America.
Subsidence-induced warming may have led to thermal decomposition of PAN
and subsequent NOx-catalyzed ozone production.
|The NCAR C-130 during a fly-by of Mount Bachelor.|
|Springtime transport of pollution from Asia, as predicted by the GMAO/GEOS-Chem chemical transport model.|