Abstract View
Chemical Characterization of Stratospheric Particles with the Next Generation of Airborne Laser Mass Spectrometer: PALMS-NG
JUSTIN JACQUOT, Xiaoli Shen, Kyra Slovacek, Gregory Schill, Michael Lawler, David Thomson, Karl Froyd, Daniel Murphy, Daniel Cziczo, Purdue University
Abstract Number: 434
Working Group: Aerosol Chemistry
Abstract
The Particle Analysis by Laser Mass Spectrometry - Next Generation (PALMS-NG) instrument has been designed and tested for use on NASA’s ER-2, a stratospheric research aircraft, to characterize in-situ the chemical composition of particles. The strong convective storms that generally occur during the summertime over North America carry out particles from the troposphere to the stratosphere. The NASA DCOTSS research project aims to get a better understanding of the chemistry and composition of the stratosphere seeded with water and pollutants originally from the troposphere.
PALMS-NG is an evolution of the existing laboratory and aircraft PALMS instruments. The main new feature consists of a bipolar time-of-flight mass spectrometer, which has a dual S shape and is named sTOF. In addition, optical improvements have led to a higher detection efficiency and larger size range of measurable particles than the original instruments. It can detect particles below 150 nm and up to several micrometers in diameter. PALMS-NG can be decomposed in two distinct parts: (1) particle detection and size estimation and (2) chemical analysis. A particle enters the instrument under vacuum through a multiple stage inlet tube to allow control of particle speed while maximizing particle transmission. First, two 405nm continuous laser beams enable an estimate of the particle size from the scattering signal analysis. Second, a 193 nm ultraviolet (UV) pulsed laser ionizes the particle. PALMS-NG bi-polar mass spectrometer has two high voltage electrodes - one positive and one negative - that separate and extract the positive and negative ions resulting from the UV pulse hit. The ions enter the sTOF mass spectrometers and ultimately impact microchannel detection plates located at each side of the instrument. The measured time-of-flight of the ions gives a mass spectrum for the identification of the chemical components that composed the detected particle.