The interplay between aqueous replacement reaction and the phase state of internally mixed organic/ammonium aerosols
<p>Atmospheric secondary aerosols are often internally mixed with organic and inorganic components, particularly dicarboxylic acids, ammonium, sulfate, nitrate, and chloride. These complex compositions enable aqueous reaction between organic and inorganic species, significantly complicating ae...
Saved in:
| Main Authors: | , , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2024-10-01
|
| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/24/11619/2024/acp-24-11619-2024.pdf |
| Tags: |
Add Tag
No Tags, Be the first to tag this record!
|
| Summary: | <p>Atmospheric secondary aerosols are often internally mixed with organic and inorganic components, particularly dicarboxylic acids, ammonium, sulfate, nitrate, and chloride. These complex compositions enable aqueous reaction between organic and inorganic species, significantly complicating aerosol phase behavior during aging and making phase predictions challenging. We investigated carboxylate–ammonium salt mixtures using attenuated total reflection Fourier-transformed infrared spectroscopy (ATR-FTIR). The mono-, di-, and tricarboxylates included sodium pyruvate (SP), sodium tartrate (ST), and sodium citrate (SC), while the ammonium salts included <span class="inline-formula">NH<sub>4</sub>NO<sub>3</sub></span>, <span class="inline-formula">NH<sub>4</sub>Cl</span>, and <span class="inline-formula">(NH<sub>4</sub>)<sub>2</sub>SO<sub>4</sub></span>. Our results demonstrated that aqueous replacement reactions between carboxylates and ammonium salts were promoted by the formation and depletion of <span class="inline-formula">NH<sub>3</sub></span> as relative humidity (RH) changed. For SP/ammonium aerosols, <span class="inline-formula">NaNO<sub>3</sub></span> and <span class="inline-formula">Na<sub>2</sub>SO<sub>4</sub></span> crystallized from 35.7 % to 12.7 % and from 65.7 % to 60.1 % RH, respectively, which is lower than the values for pure inorganics (62.5 <span class="inline-formula">±</span> 9 %–32 % RH for <span class="inline-formula">NaNO<sub>3</sub></span> and 82 <span class="inline-formula">±</span> 7 %–68 <span class="inline-formula">±</span> 5 % RH for <span class="inline-formula">Na<sub>2</sub>SO<sub>4</sub></span>). Upon hydration, the crystalline <span class="inline-formula">Na<sub>2</sub>SO<sub>4</sub></span> and <span class="inline-formula">NaNO<sub>3</sub></span> deliquesced at 88.8 %–95.2 % and 76.5 <span class="inline-formula">±</span> 2 %–81.9 %, which is higher than the values of pure <span class="inline-formula">Na<sub>2</sub>SO<sub>4</sub></span> (74 <span class="inline-formula">±</span> 4 %–98 % RH) and <span class="inline-formula">NaNO<sub>3</sub></span> (65 %–77.1 <span class="inline-formula">±</span> 3 % RH). In contrast, reaction between ST or SC and <span class="inline-formula">(NH<sub>4</sub>)<sub>2</sub>SO<sub>4</sub></span> was incomplete due to the gel structure at low RH. Unexpectedly, aqueous <span class="inline-formula">Na<sub>2</sub>SO<sub>4</sub></span> crystallized upon humidification in ST/<span class="inline-formula">(NH<sub>4</sub>)<sub>2</sub>SO<sub>4</sub></span> particles at 43.6 % RH and then deliquesced with increasing RH. This is attributed to increased ion mobility in viscous particles, leading to nucleation and growth of <span class="inline-formula">Na<sub>2</sub>SO<sub>4</sub></span> crystals. Our findings highlight the intricate interplay between chemical components within organic/inorganic aerosol and the impact of replacement reactions on aerosol aging, phase state, and subsequently atmospheric processes.</p> |
|---|---|
| ISSN: | 1680-7316 1680-7324 |