Aerosol composition of the tropical upper troposphere

Abstract

Abstract. Aerosol composition was measured by the NOAA single-particle mass spectrometer (PALMS) aboard the NASA WB-57 high altitude aircraft platform during two Aura Validation Experiment (AVE) campaigns based in Costa Rica in 2004 and 2006. These studies yielded the most complete set of aerosol composition measurements to date throughout the tropical tropopause layer (TTL) and tropical lower stratosphere. We describe the aerosol properties of the tropical atmosphere and use composition tracers to examine particle sources, the role of recent convection, and cirrus-forming potential in the TTL. Tropical dynamics and regional air sources played principal roles in dictating tropospheric aerosol properties. There was a sharp change in aerosol chemical composition at about 12 km altitude coincident with a change in convective influence. Below this level, maritime convection lofted condensable material that generated acidic, sulfate-rich aerosol. These particles contained significant amounts of methanesulfonic acid (MSA) and showed evidence of cloud processes. In contrast, continental convection injected particles and precursors directly into the TTL, yielding a population of neutralized, organic-rich aerosol. The organics were often highly oxidized and particles with oxidized organics also contained nitrate. Above the tropopause, chemical composition gradually changed toward sulfuric acid particles but neutralized particles were still abundant 2 km above the tropopause. Deep continental convection, though sporadic and geographically localized, may strongly influence TTL aerosol properties on a global scale. The abundance of organic-rich aerosol may inhibit ice nucleation and formation of tropopause level cirrus.

Organic aerosol composition and sources in Pasadena, California, during the 2010 CalNex campaign

“…These periods are more easily observed in the histogram shown in Figure A2b. The low ammonium measured-to-predicted ratios may be due to more acidic particles, but based on PALMS spectra only, about 0.1% of particles contained sulfate that was highly acidic (NH 4 + : SO 4 2À < 1) [Froyd et al, 2009]. An alternative explanation then is the presence of sodium cations that are not accounted for in Figures A2a and A2b.…”

“…In addition, the campaign average volume concentrations are summarized in the pie charts shown in Figures 3a and 3b. The particle composition types were identified from PALMS mass spectra following the method described in Froyd et al [2009]. For instance, biomass burning spectra are identified by a prominent K + peak along with organic peaks and a lack of other metals.…”

“…PM 2.5 nitrate and sulfate concentrations were measured with a ParticleInto-Liquid Sampling and Ion Chromatography (PILS-IC) system [Orsini et al, 2003]. The Particle Analysis by Laser Mass Spectrometry (PALMS) instrument provided number fractions for individual particle composition classes from 190 to 4000 nm [Froyd et al, 2009;Thomson et al, 2000]. The PALMS instrument also measures scattered light from single particles allowing for calculation of particle size in addition to particle classification.…”

Experimental evidence for excess entropy discontinuities in glass-forming solutions

“…Organic aerosol particles are, among other emission sources, produced by biomass burning in the tropics 10,11 and they are ubiquitous in the troposphere (see Kanakidou et al 12 ). Murphy et al 13 and Froyd et al 14 detected particles that consist largely of organic material at the tropical tropopause level. The high viscosity of these particles could kinetically limit water uptake and thus inhibit the formation of cirrus clouds.…”

Relationships between convective structure and transport of aerosols to the upper troposphere deduced from satellite observations

“…Aerosols in the UT typically have longer lifetime and more persistent and far-reaching radiative effects than aerosols at lower levels [Lacis et al, 1992]. Increases in aerosols in the UT can influence the formation of in situ cirrus clouds [Khain et al, 2008;Froyd et al, 2009], enhance the lifetime of convective anvil clouds [Bister and Kulmala, 2011], and increase water vapor transport into the stratosphere by distributing the water content of ice clouds among a larger number of smaller crystals [Sherwood, 2002;Bister and Kulmala, 2011;Su et al, 2011].…”