The unintended consequence of SO₂ and NO₂ regulations over China: increase of ammonia levels and impact on PM_2.5 concentrations

• Main Authors: M. Lachatre, A. Fortems-Cheiney, G. Foret, G. Siour, G. Dufour, L. Clarisse, C. Clerbaux, P.-F. Coheur, M. Van Damme, M. Beekmann
• Format: Article
• Language: English
• Published: Copernicus Publications 2019-05-01
• Series: Atmospheric Chemistry and Physics
• Online Access: https://www.atmos-chem-phys.net/19/6701/2019/acp-19-6701-2019.pdf

<p>Air pollution reaching hazardous levels in many Chinese cities has been a major concern in China over the past decades. New policies have been applied to regulate anthropogenic pollutant emissions, leading to changes in atmospheric composition and in particulate matter (<span class="inline-formula">PM</span>) production. Increasing levels of atmospheric ammonia columns have been observed by satellite during recent years. In particular, observations from the Infrared Atmospheric Sounding Interferometer (IASI) reveal an increase of these columns by 15&thinsp;% and 65&thinsp;% from 2011 to 2013 and 2015, respectively, over eastern China. In this paper we performed model simulations for 2011, 2013 and 2015 in order to understand the origin of this increase and to quantify the link between ammonia and the inorganic components of particles: <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M7" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">NH</mi><mrow><mn mathvariant="normal">4</mn><mo>(</mo><mi mathvariant="normal">p</mi><mo>)</mo></mrow><mo>+</mo></msubsup><mo>/</mo><msubsup><mi mathvariant="normal">SO</mi><mrow><mn mathvariant="normal">4</mn><mo>(</mo><mi mathvariant="normal">p</mi><mo>)</mo></mrow><mrow><mn mathvariant="normal">2</mn><mo>-</mo></mrow></msubsup><mo>/</mo><msubsup><mi mathvariant="normal">NO</mi><mrow><mn mathvariant="normal">3</mn><mo>(</mo><mi mathvariant="normal">p</mi><mo>)</mo></mrow><mo>-</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="106pt" height="19pt" class="svg-formula" dspmath="mathimg" md5hash="383a7405c287bf607266d5c594614af7"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-19-6701-2019-ie00001.svg" width="106pt" height="19pt" src="acp-19-6701-2019-ie00001.png"/></svg:svg></span></span>. Interannual change of meteorology can be excluded as a reason: year 2015 meteorology leads to enhanced sulfate production over eastern China, which increases the ammonium and decreases the ammonia content, which is contrary to satellite observations. Reductions in <span class="inline-formula">SO₂</span> and <span class="inline-formula">NO_<i>x</i></span> emissions from 2011 to 2015 of 37.5&thinsp;% and 21&thinsp;% respectively, as constrained from satellite data, lead to decreased inorganic matter (by 14&thinsp;% for <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M10" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">NH</mi><mrow><mn mathvariant="normal">4</mn><mo>(</mo><mi mathvariant="normal">p</mi><mo>)</mo></mrow><mo>+</mo></msubsup><mo>+</mo><msubsup><mi mathvariant="normal">SO</mi><mrow><mn mathvariant="normal">4</mn><mo>(</mo><mi mathvariant="normal">p</mi><mo>)</mo></mrow><mrow><mn mathvariant="normal">2</mn><mo>-</mo></mrow></msubsup><mo>+</mo><msubsup><mi mathvariant="normal">NO</mi><mrow><mn mathvariant="normal">3</mn><mo>(</mo><mi mathvariant="normal">p</mi><mo>)</mo></mrow><mo>-</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="116pt" height="19pt" class="svg-formula" dspmath="mathimg" md5hash="6b6ac4fbd711028cde370280ca4c77d5"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-19-6701-2019-ie00002.svg" width="116pt" height="19pt" src="acp-19-6701-2019-ie00002.png"/></svg:svg></span></span>). This in turn leads to increased gaseous <span class="inline-formula">NH_3(g)</span> tropospheric columns by as much as 24&thinsp;% and 49&thinsp;% (sampled corresponding to IASI data availability) from 2011 to 2013 and 2015 respectively and thus can explain most of the observed increase.</p>