Heterogeneity and chemical reactivity of the remote troposphere defined by aircraft measurements
<p>The NASA Atmospheric Tomography (ATom) mission built a photochemical climatology of air parcels based on in situ measurements with the NASA DC-8 aircraft along objectively planned profiling transects through the middle of the Pacific and Atlantic oceans. In this paper we present and analyze...
| Main Authors: | , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2021-09-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/21/13729/2021/acp-21-13729-2021.pdf |
| Summary: | <p>The NASA Atmospheric Tomography (ATom) mission built a
photochemical climatology of air parcels based on in situ measurements with
the NASA DC-8 aircraft along objectively planned profiling transects through
the middle of the Pacific and Atlantic oceans. In this paper we present and
analyze a data set of 10 s (2 km) merged and gap-filled observations of the
key reactive species driving the chemical budgets of O<span class="inline-formula"><sub>3</sub></span> and CH<span class="inline-formula"><sub>4</sub></span>
(O<span class="inline-formula"><sub>3</sub></span>, CH<span class="inline-formula"><sub>4</sub></span>, CO, H<span class="inline-formula"><sub>2</sub></span>O, HCHO, H<span class="inline-formula"><sub>2</sub></span>O<span class="inline-formula"><sub>2</sub></span>, CH<span class="inline-formula"><sub>3</sub></span>OOH,
C<span class="inline-formula"><sub>2</sub></span>H<span class="inline-formula"><sub>6</sub></span>, higher alkanes, alkenes, aromatics, NO<span class="inline-formula"><sub><i>x</i></sub></span>, HNO<span class="inline-formula"><sub>3</sub></span>,
HNO<span class="inline-formula"><sub>4</sub></span>, peroxyacetyl nitrate, other organic nitrates), consisting of
146 494 distinct air parcels from ATom deployments 1 through 4. Six models
calculated the O<span class="inline-formula"><sub>3</sub></span> and CH<span class="inline-formula"><sub>4</sub></span> photochemical tendencies from this
modeling data stream for ATom 1. We find that 80 %–90 % of the total
reactivity lies in the top 50 % of the parcels and 25 %–35 % in the top
10 %, supporting previous model-only studies that tropospheric chemistry
is driven by a fraction of all the air. In other words, accurate simulation
of the least reactive 50 % of the troposphere is unimportant for global
budgets. Surprisingly, the probability densities of species and<span id="page13730"/> reactivities
averaged on a model scale (100 km) differ only slightly from the 2 km ATom
data, indicating that much of the heterogeneity in tropospheric chemistry
can be captured with current global chemistry models. Comparing the ATom
reactivities over the tropical oceans with climatological statistics from
six global chemistry models, we find excellent agreement with the loss of
O<span class="inline-formula"><sub>3</sub></span> and CH<span class="inline-formula"><sub>4</sub></span> but sharp disagreement with production of O<span class="inline-formula"><sub>3</sub></span>. The
models sharply underestimate O<span class="inline-formula"><sub>3</sub></span> production below 4 km in both Pacific
and Atlantic basins, and this can be traced to lower NO<span class="inline-formula"><sub><i>x</i></sub></span> levels than
observed. Attaching photochemical reactivities to measurements of chemical
species allows for a richer, yet more constrained-to-what-matters, set of
metrics for model evaluation.</p> |
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| ISSN: | 1680-7316 1680-7324 |