An inversion of NO<sub><i>x</i></sub> and non-methane volatile organic compound (NMVOC) emissions using satellite observations during the KORUS-AQ campaign and implications for surface ozone over East Asia
<p>The absence of up-to-date emissions has been a major impediment to accurately simulating aspects of atmospheric chemistry and to precisely quantifying the impact of changes in emissions on air pollution. Hence, a nonlinear joint analytical inversion (Gauss–Newton method) of both volatile or...
| Main Authors: | , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2020-08-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/20/9837/2020/acp-20-9837-2020.pdf |
| Summary: | <p>The absence of up-to-date emissions has been a major impediment to
accurately simulating aspects of atmospheric chemistry and to precisely
quantifying the impact of changes in emissions on air pollution. Hence, a
nonlinear joint analytical inversion (Gauss–Newton method) of both volatile
organic compounds (VOCs) and nitrogen oxide (<span class="inline-formula">NO<sub><i>x</i></sub></span>) emissions is made by
exploiting the Smithsonian Astrophysical Observatory (SAO) Ozone Mapping and
Profiler Suite Nadir Mapper (OMPS-NM) formaldehyde (HCHO) and the National
Aeronautics and Space Administration (NASA) Ozone Monitoring Instrument
(OMI) tropospheric nitrogen dioxide (<span class="inline-formula">NO<sub>2</sub></span>) columns during the
Korea–United States Air Quality (KORUS-AQ) campaign over East Asia in
May–June 2016. Effects of the chemical feedback of <span class="inline-formula">NO<sub><i>x</i></sub></span> and VOCs on both
<span class="inline-formula">NO<sub>2</sub></span> and HCHO are implicitly included by iteratively optimizing the
inversion. Emission uncertainties are greatly narrowed (averaging
kernels <span class="inline-formula"><i>></i> 0.8</span>, which is the mathematical presentation of the
partition of information gained from the satellite observations with respect
to the prior knowledge) over medium- to high-emitting areas such as cities
and dense vegetation. The prior amount of total <span class="inline-formula">NO<sub><i>x</i></sub></span> emissions is mainly
dictated by values reported in the MIX-Asia 2010 inventory. After the
inversion we conclude that there is a decline in emissions (before, after, change) for
China (<span class="inline-formula">87.94±44.09</span> Gg d<span class="inline-formula"><sup>−1</sup></span>, <span class="inline-formula">68.00±15.94</span> Gg d<span class="inline-formula"><sup>−1</sup></span>, <span class="inline-formula">−23</span> %), North
China Plain (NCP) (<span class="inline-formula">27.96±13.49</span> Gg d<span class="inline-formula"><sup>−1</sup></span>, <span class="inline-formula">19.05±2.50</span> Gg d<span class="inline-formula"><sup>−1</sup></span>,
<span class="inline-formula">−32</span> %), Pearl River Delta (PRD) (<span class="inline-formula">4.23±1.78</span> Gg d<span class="inline-formula"><sup>−1</sup></span>, <span class="inline-formula">2.70±0.32</span> Gg d<span class="inline-formula"><sup>−1</sup></span>, <span class="inline-formula">−36</span> %), Yangtze River Delta (YRD) (<span class="inline-formula">9.84±4.68</span> Gg d<span class="inline-formula"><sup>−1</sup></span>,
<span class="inline-formula">5.77±0.51</span> Gg d<span class="inline-formula"><sup>−1</sup></span>, <span class="inline-formula">−41</span> %), Taiwan (<span class="inline-formula">1.26±0.57</span> Gg d<span class="inline-formula"><sup>−1</sup></span>,
<span class="inline-formula">0.97±0.33</span> Gg d<span class="inline-formula"><sup>−1</sup></span>, <span class="inline-formula">−23</span> %), and Malaysia (<span class="inline-formula">2.89±2.77</span> Gg d<span class="inline-formula"><sup>−1</sup></span>,
<span class="inline-formula">2.25±1.34</span> Gg d<span class="inline-formula"><sup>−1</sup></span>, <span class="inline-formula">−22</span> %), all of which have effectively implemented
various stringent regulations. In contrast, South Korea (<span class="inline-formula">2.71±1.34</span> Gg d<span class="inline-formula"><sup>−1</sup></span>, <span class="inline-formula">2.95±0.58</span> Gg d<span class="inline-formula"><sup>−1</sup></span>, <span class="inline-formula">+</span>9 %) and Japan (<span class="inline-formula">3.53±1.71</span> Gg d<span class="inline-formula"><sup>−1</sup></span>, <span class="inline-formula">3.96±1.04</span> Gg d<span class="inline-formula"><sup>−1</sup></span>, <span class="inline-formula">+12</span> %) are experiencing an increase in
<span class="inline-formula">NO<sub><i>x</i></sub></span> emissions, potentially due to an increased number of diesel vehicles and
new thermal power plants. We revisit the well-documented positive bias (by a
factor of 2 to 3) of MEGAN v2.1 (Model of Emissions of Gases and Aerosols
from<span id="page9838"/> Nature) in terms of biogenic VOC emissions in
the tropics. The inversion, however, suggests a larger growth of VOCs (mainly
anthropogenic) over NCP (25 %) than previously reported (6 %) relative
to 2010. The spatial variation in both the magnitude and sign of <span class="inline-formula">NO<sub><i>x</i></sub></span> and
VOC emissions results in nonlinear responses of ozone production and loss. Due
to a simultaneous decrease and increase in <span class="inline-formula">NO<sub><i>x</i></sub>∕VOC</span> over NCP and YRD, we
observe a <span class="inline-formula">∼53</span> % reduction in the ratio of the chemical loss
of <span class="inline-formula">NO<sub><i>x</i></sub></span> (<span class="inline-formula">LNO<sub><i>x</i></sub></span>) to the chemical loss of <span class="inline-formula">RO<sub><i>x</i></sub></span>
(<span class="inline-formula">RO<sub>2</sub>+HO<sub>2</sub></span>) over the surface transitioning toward <span class="inline-formula">NO<sub><i>x</i></sub></span>-sensitive regimes, which
in turn reduces and increases the afternoon chemical loss and production of ozone
through <span class="inline-formula">NO<sub>2</sub>+OH</span> (<span class="inline-formula">−0.42</span> ppbv h<span class="inline-formula"><sup>−1</sup></span>)<span class="inline-formula">∕HO<sub>2</sub></span> (and <span class="inline-formula">RO<sub>2</sub></span>)<span class="inline-formula">+NO</span>
(<span class="inline-formula">+0.31</span> ppbv h<span class="inline-formula"><sup>−1</sup></span>). Conversely, a combined decrease in <span class="inline-formula">NO<sub><i>x</i></sub></span> and
VOC emissions in Taiwan, Malaysia, and southern China suppresses the
formation of ozone. Simulations using the updated emissions indicate
increases in maximum daily 8 h average (MDA8) surface ozone over China
(0.62 ppbv), NCP (4.56 ppbv), and YRD (5.25 ppbv), suggesting that emission
control strategies on VOCs should be prioritized to curb ozone production
rates in these regions. Taiwan, Malaysia, and PRD stand out as regions
undergoing lower MDA8 ozone levels resulting from the <span class="inline-formula">NO<sub><i>x</i></sub></span> reductions
occurring predominantly in <span class="inline-formula">NO<sub><i>x</i></sub></span>-sensitive regimes.</p> |
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| ISSN: | 1680-7316 1680-7324 |