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  <front>
    <journal-meta><journal-id journal-id-type="publisher">ACP</journal-id><journal-title-group>
    <journal-title>Atmospheric Chemistry and Physics</journal-title>
    <abbrev-journal-title abbrev-type="publisher">ACP</abbrev-journal-title><abbrev-journal-title abbrev-type="nlm-ta">Atmos. Chem. Phys.</abbrev-journal-title>
  </journal-title-group><issn pub-type="epub">1680-7324</issn><publisher>
    <publisher-name>Copernicus Publications</publisher-name>
    <publisher-loc>Göttingen, Germany</publisher-loc>
  </publisher></journal-meta>
    <article-meta>
      <article-id pub-id-type="doi">10.5194/acp-26-12171-2026</article-id><title-group><article-title>Perchloric acid (HClO<sub>4</sub>) drives atmospheric new particle formation enhanced by dimethylamine, ammonia and sulfuric acid: mechanisms and implications</article-title><alt-title>Perchloric acid (HClO<sub>4</sub>) drives atmospheric new particle formation</alt-title>
      </title-group>
      <contrib-group>
        <contrib contrib-type="author" equal-contrib="yes" corresp="no" rid="aff2 aff3">
          <name><surname>Wang</surname><given-names>Shengming</given-names></name>
          
        </contrib>
        <contrib contrib-type="author" equal-contrib="yes" corresp="no" rid="aff4">
          <name><surname>Li</surname><given-names>Ziheng</given-names></name>
          
        </contrib>
        <contrib contrib-type="author" corresp="yes" rid="aff1">
          <name><surname>Shi</surname><given-names>Xiangli</given-names></name>
          <email>shixl@sdnu.edu.cn</email>
        </contrib>
        <contrib contrib-type="author" corresp="no" rid="aff2">
          <name><surname>Zhang</surname><given-names>Qingzhu</given-names></name>
          
        </contrib>
        <contrib contrib-type="author" corresp="no" rid="aff2">
          <name><surname>Wang</surname><given-names>Wenxing</given-names></name>
          
        </contrib>
        <aff id="aff1"><label>1</label><institution>College of Geography and Environment, Shandong Normal University, Jinan, 250014, China</institution>
        </aff>
        <aff id="aff2"><label>2</label><institution>Environment Research Institute, Shandong University, Qingdao, 266237, China</institution>
        </aff>
        <aff id="aff3"><label>3</label><institution>Laboratory of Atmospheric Environment and Pollution Control, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, 100085, China</institution>
        </aff>
        <aff id="aff4"><label>4</label><institution>Shenzhen Univ, Sch Architecture &amp; Urban Planning, Shenzhen, 518060, China</institution>
        </aff><author-comment content-type="econtrib"><p>These authors contributed equally to this work.</p></author-comment>
      </contrib-group>
      <author-notes><corresp id="corr1">Xiangli Shi (shixl@sdnu.edu.cn)</corresp></author-notes><pub-date><day>27</day><month>August</month><year>2026</year></pub-date>
      
      <volume>26</volume>
      <issue>16</issue>
      <fpage>12171</fpage><lpage>12181</lpage>
      <history>
        <date date-type="received"><day>8</day><month>April</month><year>2026</year></date>
           <date date-type="rev-request"><day>12</day><month>June</month><year>2026</year></date>
           <date date-type="rev-recd"><day>9</day><month>August</month><year>2026</year></date>
           <date date-type="accepted"><day>10</day><month>August</month><year>2026</year></date>
      </history>
      <permissions>
        <copyright-statement>Copyright: © 2026 Shengming Wang et al.</copyright-statement>
        <copyright-year>2026</copyright-year>
      <license license-type="open-access"><license-p>This work is licensed under the Creative Commons Attribution 4.0 International License. To view a copy of this licence, visit <ext-link ext-link-type="uri" xlink:href="https://creativecommons.org/licenses/by/4.0/">https://creativecommons.org/licenses/by/4.0/</ext-link></license-p></license></permissions><self-uri xlink:href="https://acp.copernicus.org/articles/26/12171/2026/acp-26-12171-2026.html">This article is available from https://acp.copernicus.org/articles/26/12171/2026/acp-26-12171-2026.html</self-uri><self-uri xlink:href="https://acp.copernicus.org/articles/26/12171/2026/acp-26-12171-2026.pdf">The full text article is available as a PDF file from https://acp.copernicus.org/articles/26/12171/2026/acp-26-12171-2026.pdf</self-uri>
      <abstract><title>Abstract</title>

      <p id="d2e158">Recent studies have revealed observations of atmospheric perchloric acid (HClO<sub>4</sub>, PA) in the Arctic. There are few studies of PA forming aerosol particles in coastal marine regions. We use quantum chemical calculations and Atmospheric Clusters Dynamic Code (ACDC) to compare the enhancement potential of dimethylamine (DMA), ammonia (NH<sub>3</sub>), and sulfuric acid (SA) for PA-based new particle formation (NPF). The results show that DMA and NH<sub>3</sub> can strongly interact with PA through hydrogen bonding and proton transfer. Compared with the nucleation of SA, PA nucleates more easily with DMA. Even if the concentration of NH<sub>3</sub> exceeds that of DMA by 10–100 orders of magnitude, the cluster formation rate of PA-DMA cluster formation is much higher than that of the PA-NH<sub>3</sub> cluster system. Clusters with the same number of PA molecules as DMA molecules play a key role in the growth of PA-DMA clusters. The present results reveal the potential for new particle formation of PA in the Arctic boundary layer.</p>
  </abstract>
    
<funding-group>
<award-group id="gs1">
<funding-source>National Natural Science Foundation of China</funding-source>
<award-id>22236004</award-id>
<award-id>22236004</award-id>
<award-id>22236004</award-id>
<award-id>42175122</award-id>
<award-id>42175122</award-id>
</award-group>
<award-group id="gs2">
<funding-source>Taishan Scholar Foundation of Shandong Province</funding-source>
<award-id>ts201712003</award-id>
</award-group>
</funding-group>
</article-meta>
  </front>
<body>
      

<sec id="Ch1.S1" sec-type="intro">
  <label>1</label><title>Introduction</title>
      <p id="d2e215">At least 50 % of the overall concentration of aerosol particles in the atmosphere is believed to be attributed to new particle formation (NPF) (Gordon et al., 2017; Takegawa et al., 2020; Williamson et al., 2019; Zhang et al., 2012; Zhao et al., 2024). Because they reflect and absorb solar radiation, reduce visibility, and have an indirect and direct impact on the climate, these aerosols have a deleterious impact on human health (Zhang, 2010). The production mechanism and subsequent expansion of aerosol particles are poorly understood, making them one of the biggest uncertainties in global climate models (Masson-Delmotte et al., 2021). Theoretical studies, laboratory experiments, and field measurements of air aerosols and nucleation events are available (Lee et al., 2019; Chu et al., 2019; Kalivitis et al., 2019). The nucleation of amines and ammonia in the atmosphere using sulfuric acid (SA) is a crucial process in the contaminated boundary layer (Chen et al., 2012; Erupe et al., 2011; Jen et al., 2014; Loukonen et al., 2010; Zhao et al., 2010; Zollner et al., 2012). Nevertheless, SA concentrations in the atmosphere are typically too low to support cluster growth to CCN size. The particle production and subsequent growth stages are significantly influenced by other nucleating agent candidates in the atmosphere.</p>
      <p id="d2e218">Abundant atmospheric bases, such as ammonia (NH<sub>3</sub>) and alkylamines (methylamine (MA), dimethylamine (DMA), trimethylamine (TMA), and ethylenediamine (EDA) are recognized as important stabilizers for H<sub>2</sub>SO<sub>4</sub>-driven nucleation (Almeida et al., 2013; Elm, 2017). A recent theoretical study found that mixed iodic acid-iodous acid (IA-HIO<sub>2</sub>) clusters account for the rapid nucleation rate under neutral conditions due to the basicity of iodous acid (HIO<sub>2</sub>) and the production of strong halogen bonds (Zhang et al., 2022b). By discovering significant perchlorate (ClO<inline-formula><mml:math id="M13" display="inline"><mml:mrow><mml:msubsup><mml:mi/><mml:mn mathvariant="normal">4</mml:mn><mml:mo>-</mml:mo></mml:msubsup></mml:mrow></mml:math></inline-formula>), recent investigations have conjectured the possible formation of perchloric acid (HClO<sub>4</sub>, PA) in the lower atmosphere (Dasgupta et al., 2005; Rajagopalan et al., 2009; Furdui and Tomassini, 2010; Barrie et al., 1988). Atmospheric PA, the sinking process of chlorine, was initially identified as a significant component in the polar stratosphere (Sander et al., 1989; Webster et al., 1993; Jaeglé et al., 1996). Tham et al. have shown the presence of chlorine oxyacids including chloric acid and PA in the Arctic region, an atmospheric sink for reactive chlorine that has not been previously considered (Tham et al., 2023). The observed concentration ranges of PA is 3 <inline-formula><mml:math id="M15" display="inline"><mml:mo>×</mml:mo></mml:math></inline-formula> 10<sup>4</sup>–1 <inline-formula><mml:math id="M17" display="inline"><mml:mo>×</mml:mo></mml:math></inline-formula> 10<sup>6</sup> cm<sup>−3</sup>in the Arctic atmosphere (Tham et al., 2023). Previous studies have found that chloric acid makes a relatively small contribution to new particle formation (Wang et al., 2025). Engsvang et al. (2024) found PA has a high nucleation potential (Engsvang et al., 2024), but the specific nucleation mechanism remain unclear. Perchloric acid is a major component of chlorine oxyacids, and its contribution to new particle formation requires further investigation (Engsvang et al., 2024). The most prevalent and powerful organic base in the environment is dimethylamine (DMA), which significantly accelerates ion-induced and neutral SA-water nucleation (Ge et al., 2011; Jen et al., 2014). During the Arctic summer, alkylamines have been detected at ppt levels (Ferrero et al., 2019). The concentration of dimethylamine (DMA) is estimated to be between 0.1 and 10 ppt.</p>
      <p id="d2e333">In this paper, the nucleation mechanism of (PA)<sub>1−4</sub>(DMA)<sub>1−4</sub>, (PA)<sub>1−4</sub>(NH<sub>3</sub>)<sub>1−4</sub>, and (PA)<sub>1−4</sub>(SA)<sub>1−4</sub> systems are investigated using quantum chemical calculations and the Atmospheric Clusters Dynamic Code (ACDC) methods. Furthermore, the relationships between various components and the thermodynamic characteristics of PA-related clusters were examined. Lastly, ACDC used dynamic simulations to examine the evaporation rates, formation paths, dimer concentrations, and particle formation rates of PA-related clusters using thermodynamic data from three PA-DMA, PA-NH<sub>3</sub>, and PA-SA systems.</p>
</sec>
<sec id="Ch1.S2">
  <label>2</label><title>Computational methods</title>
      <p id="d2e447">To find the global minimum of the (PA)<sub>1−4</sub>(DMA)<sub>1−4</sub>, (PA)<sub>1−4</sub>(NH<sub>3</sub>)<sub>1−4</sub> and (PA)<sub>1−4</sub>(SA)<sub>1−4</sub> clusters, we used a multi-step global minimum sampling approach. The ABCluster software was employed to randomly construct the initial structures of 1000–10 000 (PA)<sub>1−4</sub>(DMA)<sub>1−4</sub>, (PA)<sub>1−4</sub>(NH<sub>3</sub>)<sub>1−4</sub> and (PA)<sub>1−4</sub>(SA)<sub>1−4</sub>clusters (Zhang and Dolg, 2015). In addition, the Universal force field (UFF) (Rappé et al., 1992) was used to describe every molecule in the ABCluster software (Zhang and Dolg, 2015). Initially, from structures (<inline-formula><mml:math id="M42" display="inline"><mml:mo lspace="0mm">&gt;</mml:mo></mml:math></inline-formula> 2000) produced by the artificial bee colony algorithm (Karaboga et al., 2012) for cluster (ABCluster), 1000 structures with comparatively low energy were selected. In the multistep sampling scheme, the geometry optimization is carried out at the PM7, <inline-formula><mml:math id="M43" display="inline"><mml:mi mathvariant="italic">ω</mml:mi></mml:math></inline-formula>B97X-D/6-31<inline-formula><mml:math id="M44" display="inline"><mml:mo>+</mml:mo></mml:math></inline-formula>G(d,p) and <inline-formula><mml:math id="M45" display="inline"><mml:mi mathvariant="italic">ω</mml:mi></mml:math></inline-formula>B97X-D/6-31<inline-formula><mml:math id="M46" display="inline"><mml:mrow><mml:mo>+</mml:mo><mml:mo>+</mml:mo></mml:mrow></mml:math></inline-formula>G(d,p) levels of theory, and the single-point energy calculations are executed at the DLPNO-CCSD(T)/aug-cc-pVTZ level of theory based on the <inline-formula><mml:math id="M47" display="inline"><mml:mi mathvariant="italic">ω</mml:mi></mml:math></inline-formula>B97X-D/6-31<inline-formula><mml:math id="M48" display="inline"><mml:mrow><mml:mo>+</mml:mo><mml:mo>+</mml:mo><mml:mi>G</mml:mi></mml:mrow></mml:math></inline-formula>(d,p) theory level. The PM7 and <inline-formula><mml:math id="M49" display="inline"><mml:mi mathvariant="italic">ω</mml:mi></mml:math></inline-formula>B97X-D computations were carried out utilizing the GAUSSIAN 16 program package (Frisch et al., 2016). ORCA 4.0.0 was implemented to perform DLPNO-CCSD(T) computations (Neese, 2012). Many previous studies have adopted these methods and applied them to a wide range of acid-base cluster systems (Ning et al., 2026; Zhang et al., 2022a; Liu et al., 2023). The initial structures will be modified and re-optimized until the optimization is successful in order to address convergence issues and failures, such as terminating with a false frequency in the optimization of the (PA)<sub>1−4</sub>(DMA)<sub>1−4</sub>, (PA)<sub>1−4</sub>(NH<sub>3</sub>)<sub>1−4</sub> and (PA)<sub>1−4</sub>(SA)<sub>1−4</sub> cluster geometries. In addition, these computational methods were also applied to CA-PA cluster systems (Figs. S13–18). PA-DMA clusters' free energy of formation (<inline-formula><mml:math id="M57" display="inline"><mml:mrow><mml:mi mathvariant="normal">Δ</mml:mi><mml:mi>G</mml:mi></mml:mrow></mml:math></inline-formula>) is computed at various temperatures (238, 258, and 278 K). Previous study (Liu et al., 2023) show detailed atmospheric conditions are 253 K at April 2015 in Greenland, 268 K at May 2013 in Ny-Ålesund and 290 K at August 2019 in Helsinki. The temperatures of 238, 258, and 278 K encompass both mid-latitude coastal regions (e.g., Mace Head) and high-latitude regions (e.g., Greenland). The structures of (SA)<sub>1−4</sub>, (NH<sub>3</sub>)<sub>1−4</sub> and (DMA)<sub>1−4</sub> clusters were obtained from previous studies and are recalculated here (Xie et al., 2017; Ge et al., 2011; Jen et al., 2014; Almeida et al., 2013).</p>
<sec id="Ch1.S2.SSx1" specific-use="unnumbered">
  <title>Atmospheric Cluster Dynamics Code (ACDC) Simulation</title>
      <p id="d2e864">ACDC was applied to compute the growth pathway, steady-state concentrations, and time-evolving cluster formation rates for the (PA)<sub>1−4</sub>(DMA)<sub>1−4</sub>, (PA)<sub>1−4</sub>(NH<sub>3</sub>)<sub>1−4</sub> and (PA)<sub>1−4</sub>(SA)<sub>1−4</sub> clusters (McGrath et al., 2012). The results of the experiments employing the birth and death equations and the conclusions of the ACDC simulations correspond well (McGrath et al., 2012). In this study, ACDC simulations were performed to model the formation process of PA-DMA, PA-NH<sub>3</sub> and PA-SA neutral clusters without considering the effects of charge and water (McGrath et al., 2012). For the studied PA-DMA clusters, the <inline-formula><mml:math id="M70" display="inline"><mml:mrow><mml:msub><mml:mi mathvariant="italic">β</mml:mi><mml:mi mathvariant="normal">DMA</mml:mi></mml:msub><mml:msub><mml:mi>C</mml:mi><mml:mi mathvariant="normal">DMA</mml:mi></mml:msub><mml:mo>/</mml:mo><mml:mi mathvariant="normal">Σ</mml:mi><mml:mi mathvariant="italic">γ</mml:mi></mml:mrow></mml:math></inline-formula> of (PA)<sub>5</sub>(DMA)<sub>5</sub>cluster is greater than 1. The resulting PA-DMA systems (PA)<sub>5</sub>(DMA)<sub>5</sub> and (PA)<sub>5</sub>(DMA)<sub>4</sub> clusters are set as boundary clusters. The concentration ranges of [PA], [SA], [DMA] and [NH<sub>3</sub>] were defined at 10<sup>6</sup>–10<sup>8</sup> cm<sup>−3</sup>, 10<sup>6</sup>–10<sup>8</sup> cm<sup>−3</sup>, 0.1–100  and 1–100 ppt, respectively (Xie et al., 2017; Ge et al., 2011; Jen et al., 2014; Almeida et al., 2013).</p>
</sec>
</sec>
<sec id="Ch1.S3">
  <label>3</label><title>Results and discussion</title>
<sec id="Ch1.S3.SS1">
  <label>3.1</label><title>Cluster structures and cluster formation free energy</title>
      <p id="d2e1134">Figure 1 displays the (PA)<sub>1−4</sub>(DMA)<sub>1−4</sub> clusters identified minimum free energy configurations at the DLPNO-CCSD(T)/aug-cc-pVTZ//<inline-formula><mml:math id="M86" display="inline"><mml:mi mathvariant="italic">ω</mml:mi></mml:math></inline-formula>B97X-D/6-31<inline-formula><mml:math id="M87" display="inline"><mml:mrow><mml:mo>+</mml:mo><mml:mo>+</mml:mo></mml:mrow></mml:math></inline-formula>G(d,p) level of theory. Proton transfer and hydrogen bonding stabilize the majority of PA-DMA clusters. The formation of halogen bond is not found in PA-DMA clusters. All PA-DMA heteromolecular clusters have been discovered to undergo proton transfer, in which the hydrogen atom of hydroxyl group in the PA molecule moves to the nitrogen atom of the NH<inline-formula><mml:math id="M88" display="inline"><mml:mrow><mml:msubsup><mml:mi/><mml:mn mathvariant="normal">2</mml:mn><mml:mo>-</mml:mo></mml:msubsup></mml:mrow></mml:math></inline-formula> group in the DMA to produce N–H…O–Cl hydrogen bond. Each PA molecule donates a proton to a DMA molecule when the quantity of PA molecules and DMA molecules is equal.</p>

      <fig id="F1" specific-use="star"><label>Figure 1</label><caption><p id="d2e1196">Identified minimum free energy configurations of the (PA)<sub>1−4</sub>(DMA)<sub>1−4</sub>clusters at the DLPNO-CCSD(T)/aug-cc-pVTZ//<inline-formula><mml:math id="M91" display="inline"><mml:mi mathvariant="italic">ω</mml:mi></mml:math></inline-formula>B97X-D/6-31<inline-formula><mml:math id="M92" display="inline"><mml:mrow><mml:mo>+</mml:mo><mml:mo>+</mml:mo></mml:mrow></mml:math></inline-formula>G(d,p) level of theory. The atoms of oxygen, nitrogen, chlorine, carbon, and hydrogen are represented by the red, blue, green, gray, and white balls, respectively. Hydrogen bonds are indicated by the dashed white lines.</p></caption>
          <graphic xlink:href="https://acp.copernicus.org/articles/26/12171/2026/acp-26-12171-2026-f01.png"/>

        </fig>

      <p id="d2e1250">When the number of PA molecules is not equal to the number of DMA molecules, the number of proton transfers between PA and DMA depends on the smaller value of the number of PA or DMA molecules. In the PA-NH<sub>3</sub> cluster system (Fig. S1), NH<sub>3</sub> accepts hydrogen atoms from the hydroxyl group in PA to generate NH<inline-formula><mml:math id="M95" display="inline"><mml:mrow><mml:msubsup><mml:mi/><mml:mn mathvariant="normal">4</mml:mn><mml:mo>+</mml:mo></mml:msubsup></mml:mrow></mml:math></inline-formula> and ClO<inline-formula><mml:math id="M96" display="inline"><mml:mrow><mml:msubsup><mml:mi/><mml:mn mathvariant="normal">4</mml:mn><mml:mo>-</mml:mo></mml:msubsup></mml:mrow></mml:math></inline-formula>. It should be noted that when the number of PA molecules is greater than or equal to the number of NH<sub>3</sub> molecules, all NH<sub>3</sub> will be fully protonated. Similar to the PA-DMA cluster system, halogen bonds do not appear in the PA-NH<sub>3</sub> cluster system. The nitrogen atom of NH<sub>3</sub> and the hydrogen atom of the hydroxyl group in PA combine to form the N–H…O–Cl hydrogen bond. However, proton transfer does not take place in any of the PA-SA heteromolecular clusters (Fig. S10). Thus, hydrogen bonds (P–O…H–O and O–H…O–S) and electrostatic interactions sustain the PA-SA cluster system.</p>
      <p id="d2e1333">The <inline-formula><mml:math id="M101" display="inline"><mml:mrow><mml:mi mathvariant="normal">Δ</mml:mi><mml:mi>G</mml:mi></mml:mrow></mml:math></inline-formula> values of (PA)<sub>1−4</sub>(DMA)<sub>1−4</sub> , (PA)<sub>1−4</sub>(NH<sub>3</sub>)<sub>1−4</sub> and (PA)<sub>1−4</sub>(SA)<sub>1−4</sub> clusters at the DLPNO-CCSD(T)/aug-cc-pVTZ//<inline-formula><mml:math id="M109" display="inline"><mml:mi mathvariant="italic">ω</mml:mi></mml:math></inline-formula>B97X-D/6-31<inline-formula><mml:math id="M110" display="inline"><mml:mrow><mml:mo>+</mml:mo><mml:mo>+</mml:mo></mml:mrow></mml:math></inline-formula>G(d,p) level of 278K, are shown in Fig. 2. The <inline-formula><mml:math id="M111" display="inline"><mml:mrow><mml:mi mathvariant="normal">Δ</mml:mi><mml:mi>G</mml:mi></mml:mrow></mml:math></inline-formula> values of (PA)<sub>2</sub>, (PA)<sub>3</sub> and (PA)<sub>4</sub> clusters are <inline-formula><mml:math id="M115" display="inline"><mml:mo>-</mml:mo></mml:math></inline-formula>0.06, <inline-formula><mml:math id="M116" display="inline"><mml:mo>-</mml:mo></mml:math></inline-formula>0.99 and 2.90 kcal mol<sup>−1</sup>, respectively, indicating that pure PA molecules are thermodynamically susceptible to forming clusters. The PA-DMA cluster growth is more thermodynamically advantageous than the PA-NH<sub>3</sub> cluster growth, as indicated by the fact that all <inline-formula><mml:math id="M119" display="inline"><mml:mrow><mml:mi mathvariant="normal">Δ</mml:mi><mml:mi>G</mml:mi></mml:mrow></mml:math></inline-formula> values of the PA-DMA cluster system are lower than those of the PA-NH<sub>3</sub> cluster system. The (PA)<sub>1−4</sub>(DMA)<sub>1</sub> clusters are 15.15–38.79 kcal mol<sup>−1</sup> lower than those of the corresponding (PA)<sub>1−4</sub> clusters. The (PA)<sub>1</sub>(DMA)<sub>1</sub>, (PA)<sub>1</sub>(NH<sub>3</sub>)<sub>1</sub>, and (PA)<sub>1</sub>(SA)<sub>1</sub> initial clusters are quite significant in the corresponding cluster systems, with <inline-formula><mml:math id="M132" display="inline"><mml:mrow><mml:mi mathvariant="normal">Δ</mml:mi><mml:mi>G</mml:mi></mml:mrow></mml:math></inline-formula> values of <inline-formula><mml:math id="M133" display="inline"><mml:mo>-</mml:mo></mml:math></inline-formula>15.15, <inline-formula><mml:math id="M134" display="inline"><mml:mo>-</mml:mo></mml:math></inline-formula>9.73, and <inline-formula><mml:math id="M135" display="inline"><mml:mo>-</mml:mo></mml:math></inline-formula>4.08 kcal mol<sup>−1</sup>, respectively. The (PA)<sub>4</sub>(DMA)<sub>4</sub> cluster has the lowest <inline-formula><mml:math id="M139" display="inline"><mml:mrow><mml:mi mathvariant="normal">Δ</mml:mi><mml:mi>G</mml:mi></mml:mrow></mml:math></inline-formula> value, as low as <inline-formula><mml:math id="M140" display="inline"><mml:mo>-</mml:mo></mml:math></inline-formula>127.04 kcal mol<sup>−1</sup>. The PA-SA cluster system exhibits the greatest <inline-formula><mml:math id="M142" display="inline"><mml:mrow><mml:mi mathvariant="normal">Δ</mml:mi><mml:mi>G</mml:mi></mml:mrow></mml:math></inline-formula> values among the PA-DMA, PA-NH<sub>3</sub>, and PA-SA cluster systems, suggesting that it is a thermodynamically least stable system. In conclusion, DMA has greater potential for PA-driven nucleation than NH<sub>3</sub>and SA based on the thermodynamic data.</p>

      <fig id="F2" specific-use="star"><label>Figure 2</label><caption><p id="d2e1786">At the DLPNO-CCSD(T)/aug-cc-pVTZ//<inline-formula><mml:math id="M145" display="inline"><mml:mi mathvariant="italic">ω</mml:mi></mml:math></inline-formula>B97X-D/6-31<inline-formula><mml:math id="M146" display="inline"><mml:mrow><mml:mo>+</mml:mo><mml:mo>+</mml:mo><mml:mi>G</mml:mi></mml:mrow></mml:math></inline-formula>(d,p) level of theory, the formation free energy (<inline-formula><mml:math id="M147" display="inline"><mml:mrow><mml:mi mathvariant="normal">Δ</mml:mi><mml:mi>G</mml:mi></mml:mrow></mml:math></inline-formula>) (in kcal mol<sup>−1</sup>) of <bold>(a)</bold> (PA)<sub>1−4</sub>(DMA)<sub>1−4</sub>, <bold>(b)</bold> (PA)<sub>1−4</sub>(NH<sub>3</sub>)<sub>1−4</sub> and <bold>(c)</bold> (PA)<sub>1−4</sub>(SA)<sub>1−4</sub> clusters. The computations are carried out at 1 atm and 278 K.</p></caption>
          <graphic xlink:href="https://acp.copernicus.org/articles/26/12171/2026/acp-26-12171-2026-f02.png"/>

        </fig>

</sec>
<sec id="Ch1.S3.SS2">
  <label>3.2</label><title>Evaporation Rates and Cluster Stability</title>
      <p id="d2e1948">The stability of the PA-DMA, PA-NH<sub>3</sub>, and PA-SA cluster systems is further assessed by calculating the evaporation rates at 278 K based on the determined <inline-formula><mml:math id="M157" display="inline"><mml:mrow><mml:mi mathvariant="normal">Δ</mml:mi><mml:mi>G</mml:mi></mml:mrow></mml:math></inline-formula> values. The evaporation rate of DMA-rich clusters is higher than that of PA-rich clusters, as illustrated in Fig. 3, suggesting that clusters with more PA molecules are more stable. (PA)<sub>1</sub>(DMA)<sub>1</sub>, (PA)<sub>2</sub>(DMA)<sub>2</sub>, (PA)<sub>3</sub>(DMA)<sub>3</sub>, and (PA)<sub>4</sub>(DMA)<sub>4</sub> clusters are all highly stable, with evaporation rates of 8 <inline-formula><mml:math id="M166" display="inline"><mml:mo>×</mml:mo></mml:math></inline-formula> 10<sup>−2</sup>, 4 <inline-formula><mml:math id="M168" display="inline"><mml:mo>×</mml:mo></mml:math></inline-formula> 10<sup>−10</sup>, 2 <inline-formula><mml:math id="M170" display="inline"><mml:mo>×</mml:mo></mml:math></inline-formula> 10<sup>−5</sup>, and 4 <inline-formula><mml:math id="M172" display="inline"><mml:mo>×</mml:mo></mml:math></inline-formula> 10<sup>−5</sup> s<sup>−1</sup>, respectively. All pure PA and DMA clusters are unstable, with evaporation rates exceeding 10<sup>9</sup> s<sup>−1</sup>. The PA-rich hetero molecular clusters are more stable, probably because PA-rich clusters tend to contain more hydrogen bonds and various intermolecular interactions.</p>

      <fig id="F3" specific-use="star"><label>Figure 3</label><caption><p id="d2e2156">Evaporation rates for <bold>(a)</bold> (PA)<sub>1−4</sub>(DMA)<sub>1−4</sub> and <bold>(b)</bold> (PA)<sub>1−4</sub>(NH<sub>3</sub>)<sub>1−4</sub> <bold>(c)</bold> (PA)<sub>1−4</sub>(SA)<sub>1−4</sub> clusters at 278 K and 1 atm.</p></caption>
          <graphic xlink:href="https://acp.copernicus.org/articles/26/12171/2026/acp-26-12171-2026-f03.png"/>

        </fig>

      <p id="d2e2268">With the exception of the (PA)<sub>4</sub>(DMA)<sub>2</sub>, (PA)<sub>4</sub>(DMA)<sub>3</sub>, and (PA)<sub>4</sub>(DMA)<sub>4</sub> clusters, the evaporation rates of the majority of PA-DMA cluster systems are lower than those of the comparable clusters of PA-NH<sub>3</sub> cluster systems. Similarly, (PA)<sub>1</sub>(NH<sub>3</sub>)<sub>1</sub>, (PA)<sub>2</sub>(NH<sub>3</sub>)<sub>2</sub>, (PA)<sub>3</sub>(NH<sub>3</sub>)<sub>3</sub>, and (PA)<sub>4</sub>(NH<sub>3</sub>)<sub>4</sub> clusters are the stable clusters of the PA-NH<sub>3</sub> cluster system, which have evaporation rates of 3 <inline-formula><mml:math id="M204" display="inline"><mml:mo>×</mml:mo></mml:math></inline-formula> 10<sup>−2</sup>, 2 <inline-formula><mml:math id="M206" display="inline"><mml:mo>×</mml:mo></mml:math></inline-formula> 10<sup>−1</sup>, 3 <inline-formula><mml:math id="M208" display="inline"><mml:mo>×</mml:mo></mml:math></inline-formula> 10<sup>0</sup>, and 2 <inline-formula><mml:math id="M210" display="inline"><mml:mo>×</mml:mo></mml:math></inline-formula> 10<sup>−8</sup> s<sup>−1</sup>, respectively. (PA)<sub>1</sub>(SA)<sub>1</sub> cluster is the most stable cluster with an evaporation rate as high as 6 <inline-formula><mml:math id="M215" display="inline"><mml:mo>×</mml:mo></mml:math></inline-formula> 10<sup>6</sup> s<sup>−1</sup>, suggesting the instability of PA-SA clusters.</p>
      <p id="d2e2588">The actual Gibbs free energies of the PA-DMA systems affected by temperature and vapor concentration were calculated, as shown in Fig. 4. At 278 K, for the PA-DMA cluster system, (PA)<sub>1</sub>(DMA)<sub>1</sub>, (PA)<sub>2</sub>(DMA)<sub>2</sub>, (PA)<sub>3</sub>(DMA)<sub>3</sub>, and (PA)<sub>4</sub>(DMA)<sub>4</sub> clusters are the primary pathways and the growth process is unimpeded. The fact that the clusters on diagonal has the lowest actual free energy has also been seen in other acid-base systems (Olenius et al., 2013; Elm, 2017). The decreasing trend of the actual Gibbs free energy during the formation of the PA-DMA system is more pronounced with decreasing temperature, implying the thermodynamic stability of the PA-DMA system.</p>

      <fig id="F4"><label>Figure 4</label><caption><p id="d2e2666">Actual Gibbs free energy of the PA-DMA clusters at 278, 258 and 238 K.</p></caption>
          <graphic xlink:href="https://acp.copernicus.org/articles/26/12171/2026/acp-26-12171-2026-f04.png"/>

        </fig>

</sec>
<sec id="Ch1.S3.SS3">
  <label>3.3</label><title>Steady-State Cluster Concentrations and Nucleation Rate</title>
      <p id="d2e2683">To further assess the enhancement potential of DMA and NH<sub>3</sub> for PA-driven nucleation, the simulated steady-state PA dimer concentration (<inline-formula><mml:math id="M227" display="inline"><mml:mo lspace="0mm">∑</mml:mo></mml:math></inline-formula>[(PA)<sub>2</sub>] (cm<sup>−3</sup>)) (a) and the simulated cluster formation rate of the system, <inline-formula><mml:math id="M230" display="inline"><mml:mi>J</mml:mi></mml:math></inline-formula> (cm<sup>−3</sup> s<sup>−1</sup>) (b), at 278 K as the function of [PA] are shown in Fig. 5. It can be seen that the values of <inline-formula><mml:math id="M233" display="inline"><mml:mo>∑</mml:mo></mml:math></inline-formula>[(PA)<sub>2</sub>] and <inline-formula><mml:math id="M235" display="inline"><mml:mi>J</mml:mi></mml:math></inline-formula> of the PA-DMA system gradually increase with the increase of [PA] and [DMA] under simulated conditions. However, the effects of [PA] and [DMA] on <inline-formula><mml:math id="M236" display="inline"><mml:mo>∑</mml:mo></mml:math></inline-formula>[(PA)<sub>2</sub>] and <inline-formula><mml:math id="M238" display="inline"><mml:mi>J</mml:mi></mml:math></inline-formula> values gradually diminish with the increase of [PA] and [DMA]. In the PA-DMA system, neither <inline-formula><mml:math id="M239" display="inline"><mml:mo>∑</mml:mo></mml:math></inline-formula>[(PA)<sub>2</sub>] nor <inline-formula><mml:math id="M241" display="inline"><mml:mi>J</mml:mi></mml:math></inline-formula> values were saturated with respect to [DMA] at [DMA] <inline-formula><mml:math id="M242" display="inline"><mml:mo>=</mml:mo></mml:math></inline-formula> 0.1–10 ppt and [PA] <inline-formula><mml:math id="M243" display="inline"><mml:mo>=</mml:mo></mml:math></inline-formula> 10<sup>6</sup>–10<sup>8</sup> cm<sup>−3</sup>. <inline-formula><mml:math id="M247" display="inline"><mml:mi>J</mml:mi></mml:math></inline-formula> values for the SA-DMA cluster system were about 10<sup>−5</sup>–10<sup>0</sup> cm<sup>−3</sup> s<sup>−1</sup> at 278 K, [DMA] <inline-formula><mml:math id="M252" display="inline"><mml:mo>=</mml:mo></mml:math></inline-formula> 1 ppt and [SA] <inline-formula><mml:math id="M253" display="inline"><mml:mo>=</mml:mo></mml:math></inline-formula> 10<sup>6</sup>–10<sup>7</sup> cm<sup>−3</sup> (Xie et al., 2017). <inline-formula><mml:math id="M257" display="inline"><mml:mi>J</mml:mi></mml:math></inline-formula> values for the PA-DMA system were about 10<sup>−1</sup>–10<sup>3</sup> cm<sup>−3</sup> s<sup>−1</sup> at 278 K, [DMA] <inline-formula><mml:math id="M262" display="inline"><mml:mo>=</mml:mo></mml:math></inline-formula> 1 ppt and [PA] <inline-formula><mml:math id="M263" display="inline"><mml:mo>=</mml:mo></mml:math></inline-formula> 10<sup>6</sup>–10<sup>7</sup> cm<sup>−3</sup>. Therefore, the cluster formation rate in the PA-DMA cluster system is 3 to 4 times higher than that in the SA-DMA cluster system. Comparison of the cluster formation rates, <inline-formula><mml:math id="M267" display="inline"><mml:mi>J</mml:mi></mml:math></inline-formula> (cm<sup>−3</sup> s<sup>−1</sup>), of PA-DMA and PA-NH<sub>3</sub> systems at 278 K; [PA] <inline-formula><mml:math id="M271" display="inline"><mml:mo>=</mml:mo></mml:math></inline-formula> 10<sup>6</sup>–10<sup>8</sup> cm<sup>−3</sup>; [DMA] <inline-formula><mml:math id="M275" display="inline"><mml:mo>=</mml:mo></mml:math></inline-formula> 1 ppt; [NH<sub>3</sub>] <inline-formula><mml:math id="M277" display="inline"><mml:mo>=</mml:mo></mml:math></inline-formula> 100 ppt; CS <inline-formula><mml:math id="M278" display="inline"><mml:mo>=</mml:mo></mml:math></inline-formula> 2 <inline-formula><mml:math id="M279" display="inline"><mml:mo>×</mml:mo></mml:math></inline-formula> 10<sup>−3</sup> s<sup>−1</sup>, as shown in Fig. 5c. Even the concentrations of NH<sub>3</sub> are 2 orders of magnitude higher than those of the DMA concentration, the  <inline-formula><mml:math id="M283" display="inline"><mml:mi>J</mml:mi></mml:math></inline-formula> values of the PA-DMA cluster system are 8–10 orders of magnitude higher than those of the PA-NH<sub>3</sub> cluster system for NH<sub>3</sub>concentrations that are 2 orders of magnitude higher than those of the DMA concentration. This is not an isolated finding. For example, Ning et al. also found that the cluster formation rate of HIO<sub>3</sub>-DMA is higher than that of the HIO<sub>3</sub>-NH<sub>3</sub> cluster system (Ning et al., 2022). In addition, the trends of <inline-formula><mml:math id="M289" display="inline"><mml:mi>J</mml:mi></mml:math></inline-formula> for the PA-DMA cluster system at temperature of 238, 258 and 298 K; [PA] (10<sup>6</sup>–10<sup>8</sup> cm<sup>−3</sup>) and [DMA] (0.1, 1 and 10 ppt) are shown in Fig. 6. As the temperature decreases (from 298 to 258 K), the <inline-formula><mml:math id="M293" display="inline"><mml:mi>J</mml:mi></mml:math></inline-formula> value of the PA-DMA cluster system increases. As also discussed above, this is a direct consequence of lower <inline-formula><mml:math id="M294" display="inline"><mml:mi>T</mml:mi></mml:math></inline-formula> leading to a lower free energy and in turn leading to a lower evaporation rate. When the temperature range is 238–258 K, the <inline-formula><mml:math id="M295" display="inline"><mml:mi>J</mml:mi></mml:math></inline-formula> value of PA-DMA cluster system tends to be saturated and does not change significantly with temperature. The <inline-formula><mml:math id="M296" display="inline"><mml:mi>J</mml:mi></mml:math></inline-formula> value of the PA-DMA system is 1.65 cm<sup>−3</sup> s<sup>−1</sup> at 258 K, [DMA] <inline-formula><mml:math id="M299" display="inline"><mml:mo>=</mml:mo></mml:math></inline-formula> 1 ppt and [PA] <inline-formula><mml:math id="M300" display="inline"><mml:mo>=</mml:mo></mml:math></inline-formula> 10<sup>6</sup> cm<sup>−3</sup>.</p>

      <fig id="F5" specific-use="star"><label>Figure 5</label><caption><p id="d2e3396">Simulated steady-state PA dimer concentration <inline-formula><mml:math id="M303" display="inline"><mml:mo>∑</mml:mo></mml:math></inline-formula>[(PA)<sub>2</sub>] (cm<sup>−3</sup>) <bold>(a)</bold> and the cluster formation rates <inline-formula><mml:math id="M306" display="inline"><mml:mi>J</mml:mi></mml:math></inline-formula> (cm<sup>−3</sup> s<sup>−1</sup>) of the simulation systems <bold>(b)</bold> as a function of [PA] at 278 K. <bold>(c)</bold> Comparison of the cluster formation rates <inline-formula><mml:math id="M309" display="inline"><mml:mi>J</mml:mi></mml:math></inline-formula> (cm<sup>−3</sup> s<sup>−1</sup>) of PA-DMA clusters with PA-NH<sub>3</sub> clusters at 278 K; [PA] <inline-formula><mml:math id="M313" display="inline"><mml:mo>=</mml:mo></mml:math></inline-formula> 10<sup>6</sup>–10<sup>8</sup> cm<sup>−3</sup>; [DMA] <inline-formula><mml:math id="M317" display="inline"><mml:mo>=</mml:mo></mml:math></inline-formula> 1 ppt; [NH<sub>3</sub>] <inline-formula><mml:math id="M319" display="inline"><mml:mo>=</mml:mo></mml:math></inline-formula> 100 ppt; and CS <inline-formula><mml:math id="M320" display="inline"><mml:mo>=</mml:mo></mml:math></inline-formula> 2 <inline-formula><mml:math id="M321" display="inline"><mml:mo>×</mml:mo></mml:math></inline-formula> 10<sup>−3</sup> s<sup>−1</sup>. The <inline-formula><mml:math id="M324" display="inline"><mml:mrow><mml:mi mathvariant="normal">Δ</mml:mi><mml:mi>G</mml:mi></mml:mrow></mml:math></inline-formula> values at the DLPNO-CCSD(T)/aug-cc-pVTZ//<inline-formula><mml:math id="M325" display="inline"><mml:mi mathvariant="italic">ω</mml:mi></mml:math></inline-formula>B97X-D/6-31<inline-formula><mml:math id="M326" display="inline"><mml:mrow><mml:mo>+</mml:mo><mml:mo>+</mml:mo></mml:mrow></mml:math></inline-formula>G(d,p) level are used to compute the PA-DMA and PA-NH<sub>3</sub> rates.</p></caption>
          <graphic xlink:href="https://acp.copernicus.org/articles/26/12171/2026/acp-26-12171-2026-f05.png"/>

        </fig>

      <fig id="F6" specific-use="star"><label>Figure 6</label><caption><p id="d2e3653">The simulated cluster formation rate <inline-formula><mml:math id="M328" display="inline"><mml:mi>J</mml:mi></mml:math></inline-formula> (cm<sup>−3</sup> s<sup>−1</sup>) of the PA-DMA system at different temperatures <bold>(A)</bold> 238, <bold>(B)</bold> 258, and <bold>(C)</bold> 298 K; [PA] <inline-formula><mml:math id="M331" display="inline"><mml:mo>=</mml:mo></mml:math></inline-formula> 10<sup>6</sup>–10<sup>8</sup> cm<sup>−3</sup>; [DMA] <inline-formula><mml:math id="M335" display="inline"><mml:mo>=</mml:mo></mml:math></inline-formula> 0.1, 1, and 10 ppt; and CS <inline-formula><mml:math id="M336" display="inline"><mml:mo>=</mml:mo></mml:math></inline-formula>  2 <inline-formula><mml:math id="M337" display="inline"><mml:mo>×</mml:mo></mml:math></inline-formula> 10<sup>−3</sup> s<sup>−1</sup>.</p></caption>
          <graphic xlink:href="https://acp.copernicus.org/articles/26/12171/2026/acp-26-12171-2026-f06.png"/>

        </fig>

</sec>
<sec id="Ch1.S3.SS4">
  <label>3.4</label><title>Cluster Growth Route</title>
      <p id="d2e3794">The growth routes of the PA-DMA (a) and PA-NH<sub>3</sub> (b) systems at 278 K, [PA] <inline-formula><mml:math id="M341" display="inline"><mml:mo>=</mml:mo></mml:math></inline-formula> 10<sup>6</sup> cm<sup>−3</sup>, [DMA] <inline-formula><mml:math id="M344" display="inline"><mml:mo>=</mml:mo></mml:math></inline-formula> 3 ppt, and [NH<sub>3</sub>] <inline-formula><mml:math id="M346" display="inline"><mml:mo>=</mml:mo></mml:math></inline-formula> 100 ppt are shown in Fig. 7. The evaporation rates of (PA)<sub>2</sub>and (DMA)<sub>2</sub> clusters are 4 <inline-formula><mml:math id="M349" display="inline"><mml:mo>×</mml:mo></mml:math></inline-formula> 10<sup>9</sup> and 2 <inline-formula><mml:math id="M351" display="inline"><mml:mo>×</mml:mo></mml:math></inline-formula> 10<sup>12</sup> s<sup>−1</sup>. The higher evaporation rate causes the PA-DMA system to form via the (PA)<sub>1</sub>(DMA)<sub>1</sub> dimer pathway rather than via the (PA)<sub>2</sub> and (DMA)<sub>2</sub> cluster pathways. The formation of the (PA)<sub>1</sub>(DMA)<sub>1</sub> dimer is the initial stage in the PA-DMA system. There is no branching during the growth of clusters of the PA-DMA system, which may be due to the fact that the evaporation rate of clusters on the diagonal (the number of PA molecules is the same as the number of DMA molecules) is much lower than that of clusters off the diagonal (the number of PA molecules is different from the number of DMA molecules). A (PA)<sub>2</sub>(DMA)<sub>2</sub> cluster complex is then formed by the combination of two (PA)<sub>1</sub>(DMA)<sub>1</sub> dimer clusters.</p>

      <fig id="F7" specific-use="star"><label>Figure 7</label><caption><p id="d2e4015"><bold>(a)</bold> Main clustering routes of (PA)<sub>1−4</sub>(DMA)<sub>1−4</sub> clusters at 278 K, [PA] <inline-formula><mml:math id="M366" display="inline"><mml:mo>=</mml:mo></mml:math></inline-formula> 10<sup>6</sup> cm<sup>−3</sup>, and [DMA] <inline-formula><mml:math id="M369" display="inline"><mml:mo>=</mml:mo></mml:math></inline-formula> 3 ppt. <bold>(b)</bold> Main clustering routes of (PA)<sub>1−4</sub>(NH<sub>3</sub>)<sub>1−4</sub> clusters at 278 K, [PA] <inline-formula><mml:math id="M373" display="inline"><mml:mo>=</mml:mo></mml:math></inline-formula> 10<sup>6</sup> cm<sup>−3</sup>, and [NH<sub>3</sub>] <inline-formula><mml:math id="M377" display="inline"><mml:mo>=</mml:mo></mml:math></inline-formula> 100 ppt.</p></caption>
          <graphic xlink:href="https://acp.copernicus.org/articles/26/12171/2026/acp-26-12171-2026-f07.png"/>

        </fig>

      <p id="d2e4175">(PA)<sub>2</sub>(DMA)<sub>2</sub> also has only one growth path and further collides with (PA)<sub>1</sub>(DMA)<sub>1</sub> to form a (PA)<sub>3</sub>(DMA)<sub>3</sub> cluster. Eventually (PA)<sub>5</sub>(DMA)<sub>5</sub> clusters is stable enough to grow from the PA-DMA system. Therefore, collision between clusters with PA and DMA monomers is not the main way in the PA-DMA cluster system. Cluster coalescence between a large number of (PA)<sub>1</sub>(DMA)<sub>1</sub> clusters play an important role in the growth of PA-DMA clusters, which may be due to the low evaporation rate and high stability of (PA)<sub>1</sub>(DMA)<sub>1</sub>, (PA)<sub>2</sub>(DMA)<sub>2</sub>, (PA)<sub>3</sub>(DMA)<sub>3</sub>, and (PA)<sub>4</sub>(DMA)<sub>4</sub> clusters. This is a usual property of acid-base clusters (Lu et al., 2020). The growth path of the PA-NH<sub>3</sub> cluster system is very similar to that of the PA-DMA cluster system, in which a PA monomer molecule collides with an NH<sub>3</sub> molecule to form a (PA)<sub>1</sub>(NH<sub>3</sub>)<sub>1</sub> dimer cluster, and then (PA)<sub>1</sub>(NH<sub>3</sub>)<sub>1</sub> dimer clusters are continuously added to form (PA)<sub>4</sub>(NH<sub>3</sub>)<sub>4</sub> cluster.</p>
</sec>
</sec>
<sec id="Ch1.S4" sec-type="conclusions">
  <label>4</label><title>Atmospheric Implications and Conclusion</title>
      <p id="d2e4452">In this paper, quantum chemical methods are used to study the energy minimum configurations for the formation of atmospheric clusters of PA with DMA, NH<sub>3</sub> and SA in the Arctic boundary layer. The evaporation rates, cluster formation rates and growth paths of the nucleation process of PA with DMA, NH<sub>3</sub> and SA clusters are simulated by inputting ACDC from the thermodynamic data obtained. The following conclusions were drawn: <list list-type="order"><list-item>
      <p id="d2e4475">Based on the Gibbs free energies calculated in this study, DMA and NH<sub>3</sub> can strongly interact with PA through hydrogen bonding and proton transfer, thus promoting the formation of PA-DMA and PA-NH<sub>3</sub> clusters. No halogen bonds are found in PA-DMA and PA-NH<sub>3</sub> clusters.</p></list-item><list-item>
      <p id="d2e4506">Under the condition that the DMA concentration is two orders of magnitude lower than the NH<sub>3</sub> concentration, the formation rate of PA-DMA clusters is much faster than that of PA-NH<sub>3</sub> clusters. The cluster formation rate of the PA-SA cluster system is the slowest among the three systems. This may be due to the fact that no proton transfer occurs between the PA and SA molecules and only hydrogen bonding stabilizes the clusters.</p></list-item><list-item>
      <p id="d2e4528">The formation rate of pure PA clusters is extremely low. DMA can promote the formation rate of PA clusters to a high level, which reflects the stabilizing effect of DMA on PA clusters. The results suggest that PA can contribute to new particle formation in the Arctic. The formation of (PA)<sub>1</sub>(DMA)<sub>1</sub> and (PA)<sub>1</sub>(NH<sub>3</sub>)<sub>1</sub> dimers are the decisive clusters for the growth of PA-DMA and PA-NH<sub>3</sub> cluster systems.</p></list-item><list-item>
      <p id="d2e4587">PA can form stable binary clusters with DMA, which is an important step in the formation of new particles in the atmosphere. The nucleation mechanism of PA-DMA revealed in this study may contribute to a deeper understanding of the role of marine chlorine-containing components on marine NPF.</p></list-item></list></p>
      <p id="d2e4590">Previous views hold that nucleation involving sulfuric acid/iodine oxoacid and amines/ammonia is a key pathway for new particle formation in the polluted boundary layer. The results of this study provide a partial explanation for the “fate” of PA in the Arctic atmosphere: PA can not only be removed via wet and dry deposition but is also likely to participate in new particle formation by reacting with basic gases (especially DMA) to form stable clusters. This provides a theoretical basis for understanding the role of chlorine-containing components, particularly previously overlooked chlorate, in tropospheric aerosol nucleation. In a region where conventional sulfuric acid-amine/ammonia nucleation is often limited by low precursor concentrations, this PA-DMA pathway offers an additional source of ultrafine particles that can grow into cloud condensation nuclei. This has direct consequences for CCN budgets and, consequently, for cloud microphysical properties and shortwave radiative forcing over the Arctic and other remote marine environments.</p>
      <p id="d2e4593">This study indicates that perchloric acid has potential in new particle formation in the Arctic marine boundary layer, particularly in the presence of dimethylamine. This finding has significant atmospheric and climatic implications: first, it reveals a potential new and efficient nucleation pathway between active chlorine released from the ocean (via the formation of HClO<sub>4</sub>) and nitrogen-containing bases (such as DMA from marine biogenic sources), which may have important implications for assessing the number of cloud condensation nuclei and cloud radiative forcing in the marine boundary layer. Second, it expands our understanding of the atmospheric chlorine cycle, indicating that, in addition to known deposition processes, gas-to-particle transformations involving basic gases represent an important atmospheric “sink” for HClO<sub>4</sub>. This additional sink may influence the atmospheric residence time and vertical profile of HClO<sub>4</sub>, with potential ramifications for oxidative capacity and halogen-mediated chemistry in the polar troposphere. These findings underscore the need to revisit how chlorine-containing species are represented in global and regional climate models. Current Earth system models typically neglect HClO<sub>4</sub> and its interaction with amines in aerosol nucleation schemes. Incorporating the PA-DMA nucleation mechanism, especially in high-latitude and marine domains, could improve simulations of aerosol-cloud-climate interactions.</p>
</sec>

      
      </body>
    <back><notes notes-type="dataavailability"><title>Data availability</title>

      <p id="d2e4637">All data supported the paper are available from the article, Supplement, and the corresponding author upon reasonable request.</p>
  </notes><app-group>
        <supplementary-material position="anchor"><p id="d2e4640">The supplement related to this article is available online at <inline-supplementary-material xlink:href="https://doi.org/10.5194/acp-26-12171-2026-supplement" xlink:title="pdf">https://doi.org/10.5194/acp-26-12171-2026-supplement</inline-supplementary-material>.</p></supplementary-material>
        </app-group><notes notes-type="authorcontribution"><title>Author contributions</title>

      <p id="d2e4649">SW: Investigation, Conceptualization, Formal analysis, Data curation, Writing-original draft.  ZL: Investigation, Conceptualization, Data curation. XS: Methodology, Writing-reviewing and editing, Validation, Supervision. QZ: Methodology, Validation, Supervision, Funding acquisition. WW: Resources, Funding acquisition, Writing-reviewing and editing Supervision.</p>
  </notes><notes notes-type="competinginterests"><title>Competing interests</title>

      <p id="d2e4655">The contact author has declared that none of the authors has any competing interests.</p>
  </notes><notes notes-type="disclaimer"><title>Disclaimer</title>

      <p id="d2e4661">Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. The authors bear the ultimate responsibility for providing appropriate place names. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.</p>
  </notes><ack><title>Acknowledgements</title><p id="d2e4667">The work was financially supported by National Natural Science Foundation of China (project No. 22236004, 21976107, 42075106, 42175122, 4217050207) and Taishan Scholar Foundation of Shandong Province (No. ts201712003).</p></ack><notes notes-type="financialsupport"><title>Financial support</title>

      <p id="d2e4672">This research has been supported by the National Natural Science Foundation of China (grant nos. 22236004, 22236004, 22236004, 42175122, and 42175122) and the Taishan Scholar Foundation of Shandong Province (grant no. ts201712003).</p>
  </notes><notes notes-type="reviewstatement"><title>Review statement</title>

      <p id="d2e4678">This paper was edited by Markus Petters and reviewed by Jonas Elm and two anonymous referees.</p>
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