Global-scale seasonally resolved black carbon vertical profiles over the Pacific

Abstract

[1] Black carbon (BC) aerosol loadings were measured during the High-performance Instrumented Airborne Platform for Environmental Research Pole-to-Pole Observations (HIPPO) campaign above the remote Pacific from 85°N to 67°S. Over 700 vertical profiles extending from near the surface to max ∼14 km altitude were obtained with a single-particle soot photometer between early 2009 and mid-2011. The data provides a climatology of BC in the remote regions that reveals gradients of BC concentration reflecting global-scale transport and removal of pollution. BC is identified as a sensitive tracer of extratropical mixing into the lower tropical tropopause layer and trends toward surprisingly uniform loadings in the lower stratosphere of ∼1 ng/kg. The climatology is compared to predictions from the AeroCom global model intercomparison initiative. The AeroCom model suite overestimates loads in the upper troposphere/lower stratosphere (∼10×) more severely than at lower altitudes (∼3×), with bias roughly independent of season or geographic location; these results indicate that it overestimates BC lifetime.

Keywords: AeroCom; HIPPO; aerosol; black carbon; remote; tropical tropopause layer.

Figure 1

Map showing the flight track of the NSF/NCAR GV on HIPPO series 1–5 (HIPPO 1: January 2009, red; HIPPO 2: November 2009, orange; HIPPO 3, March/April 2010, green; HIPPO 4, June 2011, blue; HIPPO 5, August, 2011, purple). The markers represent the central location of each vertical profile and are only included for profiles with at least two valid 1 km altitude average BC MMR values. The colored bands show the regions averaged for comparison to models. On the right axes are shown the number of profiles in each latitude band from each HIPPO flight set.).

Figure 2

Measured and modeled vertical BC profiles in five latitude bands. The measured profiles are colored from red to purple throughout a calendar year, with the thick black line providing their average (and an approximate annual average). The AeroCom model suite average profile is the thick darker blue line, with 25th and 75th percentile values given by the thin darker blue lines. Shown in grey, as a guide to the eye, is 1 ng rBC/kg mass mixing ratio.

Figure 3

Trends in rBC MMR across the TTL. (left) The rBC MMR from the entire HIPPO data set at two potential temperature (theta) ranges is plotted against latitude. (right) The vertical profile of rBC MMR for the tropics (as in Figure 2) is plotted against potential temperature with the extratropical profile generated by averaging the profiles from south and north 20°–50°. The tropical profile and its minimum are extrapolated to 1 ng rBC/kg at 360 K, as represented by the gray extension and circled point, and the dashed line, respectively.

Figure 4

The ratio of the modeled to measured vertical BC profiles for individual latitude bands (colored lines) and averaged overall latitudes (black line). These results are averaged over all seasons/HIPPO series.