METHOD TO QUANTIFY EMISSION RATES IN ATMOSPHERIC PLUMES

摘要

A new method of making sky-LOSA measurements (Line-Of-Sight Attenuation measurements of sky-light) of soot mass flux in atmospheric plumes has been developed which enables accurate measurements in the presence of in-scattered light from the sky and sun.

主权项

1. A method of determining a spatially resolved reference transmissivity field (τ*) of an atmospheric plume, the method comprising:
obtaining a spatially resolved measurement of plume and adjacent skylight intensity (ILOSM) using an optical detection system, the optical axis for the measurement being the optical axis of the detection system, which transects the atmospheric plume and has an angle β relative to horizontal; calculating an apparent transmissivity field (τexp) as a ratio of spatially resolved ILOSM and ILOS0 data where ILOS0 is a spatially resolved reference background sky-intensity in a region of the sky behind the atmospheric plume; calculating a relative contribution of in-scattered sky-light, B, in accordance with eq. 6bBILOS0=1ILOS0∫0π2∫02πIsky(α,Z)σaggsc(θ(α,Z))Ωvv_(1+cos2θ(α,Z)2)sinZαZ(6b) where
Isky(α,Z) is a radiance originating from a location in the sky specified by angles α and Z [W M−2ster−1];α is an azimuth angle between a first plane and a second plane, the first plane containing the sun and a measurement zenith axis and the second plane containing a position in the sky of interest and the measurement zenith axis, where the azimuth angle is defined to be positive in a clockwise direction relative to the first plane when looking down to the surface of the earth and the measurement zenith axis is defined as a vertical axis relative to the surface of the earth originating at a measurement location;Z is a zenith angle between a line connecting a position in the sky of interest and the measurement zenith axis, the zenith angle being equal to zero when the position of the sky is directly above the measurement location;(α,Z) is an angle between a line connecting the measurement location and the position in the sky of interest, defined by the angles α and Z, and a second line defined by the optical axis of the optical detection system, the angle θ being equal to zero when the position in the sky is intersected by the optical axis;σaggsc(θ(α,Z))Ωvv_ is the effective differential scattering cross-section of a soot aggregate with respect to solid angle, Ω, and is a function of the scattering angle, θ [m2 ster−1] and the subscript ‘vv’ indicates vertical polarization of both the incident and scattered light; calculating of a ratio of sun intensity to sky intensity behind the atmospheric plume(EsunILOS0)  using measured data for intensity of the sun in the sky; calculating a contribution of in-scattered sun-light, C, in accordance with eq. 6cCILOS0=EsunILOS0σaggsc(θsun)Ωvv_1+cos2θsun2(6c)  where θsun is an angle between a line connecting the measurement location and the sun and a second line defined by the optical axis of the optical detection system, the angle θsun being equal to zero when the optical detection system's optical axis intersects the sun; calculating the reference transmissivity in accordance with eq. 16τ*=(τexp-B+CILOS0σaggext_)(1-B+CILOS0σaggext_)-1(16)  where σaggext is the measured or calculated extinction coefficient of the target constituents of the plume at a specified measurement wavelength band; and outputting the reference transmissivity to an output device.