Emissions relationships in western forest fire plumes – Part 1: Reducing the effect of mixing errors on emission factors
<p>Studies of emission factors from biomass burning using aircraft data complement the results of lab studies and extend them to conditions of immense hot conflagrations. A new theoretical development of plume theory for multiple tracers is developed after examining aircraft samples. We illust...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2020-12-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | https://amt.copernicus.org/articles/13/7069/2020/amt-13-7069-2020.pdf |
| Summary: | <p>Studies of emission factors from biomass burning using
aircraft data complement the results of lab studies and extend them to
conditions of immense hot conflagrations. A new theoretical development of
plume theory for multiple tracers is developed after examining aircraft
samples. We illustrate and discuss emissions relationships for 422 individual
samples from many forest fire plumes in the Western USA. Samples are from
two NASA investigations: ARCTAS (Arctic Research of the Composition of the
Troposphere from Aircraft and Satellites) and SEAC4RS (Studies of Emissions
and Atmospheric Composition, Clouds and Climate Coupling by Regional
Surveys). This work provides sample-by-sample enhancement ratios (EnRs) for
23 gases and particulate properties. Many EnRs provide candidates for
emission ratios (ERs, corresponding to the EnR at the source) when the
origin and degree of transformation is understood. From these, emission
factors (EFs) can be estimated, provided the fuel dry mass consumed is known
or can be estimated using the carbon mass budget approach. This analysis
requires understanding the interplay of mixing of the plume with surrounding
air. Some initial examples emphasize that measured <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M1" display="inline" overflow="scroll" dspmath="mathml"><mrow><msub><mi>C</mi><mi mathvariant="normal">tot</mi></msub><mo>=</mo><mrow class="chem"><msub><mi mathvariant="normal">CO</mi><mn mathvariant="normal">2</mn></msub></mrow><mo>+</mo><mrow class="chem"><mi mathvariant="normal">CO</mi></mrow></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="81pt" height="13pt" class="svg-formula" dspmath="mathimg" md5hash="84305589fa4e90cbb65d6f0136852b6c"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-13-7069-2020-ie00001.svg" width="81pt" height="13pt" src="amt-13-7069-2020-ie00001.png"/></svg:svg></span></span> in a fire plume does not necessarily describe the emissions of the
total carbon liberated in the flames, <span class="inline-formula"><i>C</i><sub>burn</sub></span>. Rather, it represents
<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M3" display="inline" overflow="scroll" dspmath="mathml"><mrow><msub><mi>C</mi><mi mathvariant="normal">tot</mi></msub><mo>=</mo><msub><mi>C</mi><mi mathvariant="normal">burn</mi></msub><mo>+</mo><msub><mi>C</mi><mi mathvariant="normal">bkgd</mi></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="92pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="d7b80c67dccc42d28c3657949673d67e"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-13-7069-2020-ie00002.svg" width="92pt" height="14pt" src="amt-13-7069-2020-ie00002.png"/></svg:svg></span></span>, which includes possibly varying
background concentrations for entrained air. Consequently, we present a
simple theoretical description for plume entrainment for multiple tracers
from the flame tops to hundreds of kilometers downwind and illustrate some intrinsic
linear behaviors. The analysis suggests a mixed-effects regression emission
technique (MERET), which can eliminate occasional strong biases associated
with the commonly used normalized excess mixing ratio (NEMR) method. MERET
splits <span class="inline-formula"><i>C</i><sub>tot</sub></span> to reveal <span class="inline-formula"><i>C</i><sub>burn</sub></span> by exploiting the fact that <span class="inline-formula"><i>C</i><sub>burn</sub></span>
and all tracers respond linearly to dilution, while each tracer has
consistent EnR behavior (slope of tracer concentration with respect to
<span class="inline-formula"><i>C</i><sub>burn</sub></span>). The two effects are separable. Two or three or preferably more
emission indicators are required as a minimum; here we used eight. In
summary, MERET allows a fine spatial resolution (EnRs for individual
observations) and comparison of similar plumes that are distant in time and space.
Alkene ratios provide us with an approximate photochemical timescale. This
allows discrimination and definition, by fire situation, of ERs, allowing us
to estimate emission factors.</p> |
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| ISSN: | 1867-1381 1867-8548 |