Impact of particle number and mass size distributions of major chemical components on particle mass scattering efficiency in urban Guangzhou in southern China

• Main Authors: J. Tao, Z. Zhang, Y. Wu, L. Zhang, Z. Wu, P. Cheng, M. Li, L. Chen, R. Zhang, J. Cao
• Format: Article
• Language: English
• Published: Copernicus Publications 2019-07-01
• Series: Atmospheric Chemistry and Physics
• Online Access: https://www.atmos-chem-phys.net/19/8471/2019/acp-19-8471-2019.pdf
• ISSN: 1680-7316; 1680-7324

<p>To grasp the key factors affecting particle mass scattering efficiency (MSE), particle mass and number size distribution, PM<span class="inline-formula">_2.5</span> and PM<span class="inline-formula">₁₀</span> and their major chemical compositions, and the particle scattering coefficient (<span class="inline-formula"><i>b</i>_sp</span>) under dry conditions were measured at an urban site in Guangzhou, southern China, during 2015–2016. On an annual average, <span class="inline-formula">10±2</span>&thinsp;%, <span class="inline-formula">48±7</span>&thinsp;% and <span class="inline-formula">42±8</span>&thinsp;% of PM<span class="inline-formula">₁₀</span> mass were in the condensation, droplet and coarse modes, respectively, with mass mean aerodynamic diameters (MMADs) of <span class="inline-formula">0.78±0.07</span> in the droplet mode and <span class="inline-formula">4.57±0.42</span>&thinsp;<span class="inline-formula">µm</span> in the coarse mode. The identified chemical species mass concentrations can explain <span class="inline-formula">79±3</span>&thinsp;%, <span class="inline-formula">82±6</span>&thinsp;% and <span class="inline-formula">57±6</span>&thinsp;% of the total particle mass in the condensation, droplet and coarse mode, respectively. Organic matter (OM) and elemental carbon (EC) in the condensation mode, OM, <span class="inline-formula">(NH₄)₂SO₄</span>, <span class="inline-formula">NH₄NO₃</span>, and crustal element oxides in the droplet mode, and crustal element oxides, OM, and <span class="inline-formula">CaSO₄</span> in the coarse mode, were the dominant chemical species in their respective modes. The measured <span class="inline-formula"><i>b</i>_sp</span> can be reconstructed to the level of <span class="inline-formula">91±10</span>&thinsp;% using Mie theory with input of the estimated chemically resolved number concentrations of NaCl, <span class="inline-formula">NaNO₃</span>, <span class="inline-formula">Na₂SO₄</span>, <span class="inline-formula">NH₄NO₃</span>, <span class="inline-formula">(NH₄)₂SO₄</span>, <span class="inline-formula">K₂SO₄</span>, <span class="inline-formula">CaSO₄</span>, <span class="inline-formula">Ca(NO₃)₂</span>, OM, EC, crustal element oxides and unidentified fraction. MSEs of particle and individual chemical species were underestimated by less than 13&thinsp;% in any season based on the estimated <span class="inline-formula"><i>b</i>_sp</span> and chemical species mass concentrations. Seasonal average MSEs varied in the range of <span class="inline-formula">3.5±0.1</span> to <span class="inline-formula">3.9±0.2</span>&thinsp;m<span class="inline-formula">²</span>&thinsp;g<span class="inline-formula">⁻¹</span> for fine particles (aerodynamic diameter smaller than 2.1&thinsp;<span class="inline-formula">µm</span>), which was mainly caused by seasonal variations in the mass fractions and MSEs of the dominant chemical species (OM, <span class="inline-formula">NH₄NO₃</span>, <span class="inline-formula">(NH₄)₂SO₄</span>) in the droplet mode. MSEs of the dominant chemical species were determined by their lognormal size-distribution parameters, including MMADs and standard deviation (<span class="inline-formula"><i>σ</i></span>) in the droplet mode.</p>