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Measuring and modeling investigation of the net photochemical ozone production rate via an improved dual-channel reaction chamber technique
oleh: Y. Hao, Y. Hao, J. Zhou, J. Zhou, J.-P. Zhou, J.-P. Zhou, Y. Wang, Y. Wang, S. Yang, S. Yang, Y. Huangfu, Y. Huangfu, X.-B. Li, X.-B. Li, C. Zhang, A. Liu, Y. Wu, Y. Wu, Y. Zhou, Y. Zhou, S. Yang, S. Yang, Y. Peng, Y. Peng, J. Qi, J. Qi, X. He, X. He, X. Song, X. Song, Y. Chen, Y. Chen, B. Yuan, B. Yuan, M. Shao, M. Shao
Format: | Article |
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Diterbitkan: | Copernicus Publications 2023-09-01 |
Deskripsi
<p>Current process-based research mainly uses box models to evaluate photochemical ozone production and destruction rates, and it is unclear to what extent the photochemical reaction mechanisms are elucidated. Here, we modified and improved a net photochemical ozone production rate (NPOPR, <span class="inline-formula"><i>P</i></span>(O<span class="inline-formula"><sub>3</sub></span>)<span class="inline-formula"><sub>net</sub></span>) detection system based on the current dual-channel reaction chamber technique, which makes the instrument applicable to different ambient environments, and its various operating indicators were characterized, i.e., “airtightness”, light transmittance, wall losses of the reaction and reference chambers, conversion rate of O<span class="inline-formula"><sub>3</sub></span> to NO<span class="inline-formula"><sub>2</sub></span>, air residence time, and performance of the reaction and reference chambers. The limits of detection of the NPOPR detection system were determined to be 0.07, 1.4, and 2.3 ppbv h<span class="inline-formula"><sup>−1</sup></span> at sampling flow rates of 1.3, 3, and 5 L min<span class="inline-formula"><sup>−1</sup></span>, respectively. We further applied the NPOPR detection system to field observations at an urban site in the Pearl River Delta (China). During the observation period, the maximum value of <span class="inline-formula"><i>P</i></span>(O<span class="inline-formula"><sub>3</sub></span>)<span class="inline-formula"><sub>net</sub></span> was 34.1 ppbv h<span class="inline-formula"><sup>−1</sup></span>, which was <span class="inline-formula">∼</span> 0 ppbv h<span class="inline-formula"><sup>−1</sup></span> at night within the system detection error and peaked at approximately noon local time. The daytime (from 06:00–18:00 LT) average value of <span class="inline-formula"><i>P</i></span>(O<span class="inline-formula"><sub>3</sub></span>)<span class="inline-formula"><sub>net</sub></span> was 12.8 (<span class="inline-formula">±</span> 5.5) ppbv h<span class="inline-formula"><sup>−1</sup></span>. We investigated the detailed photochemical O<span class="inline-formula"><sub>3</sub></span> formation mechanism in the reaction and reference chambers of the NPOPR detection system using a zero-dimensional box model. We found that the photochemical reactions in the reaction chamber were very close to those in ambient air, but there was not zero chemistry in the reference chamber because the reaction related to the production and destruction of RO<span class="inline-formula"><sub>2</sub></span> (<span class="inline-formula">=</span> HO<span class="inline-formula"><sub>2</sub></span> <span class="inline-formula">+</span> RO<span class="inline-formula"><sub>2</sub></span>) continued in the reference chamber, which led to a small amount of <span class="inline-formula"><i>P</i></span>(O<span class="inline-formula"><sub>3</sub></span>)<span class="inline-formula"><sub>net</sub></span>. Therefore, the <span class="inline-formula"><i>P</i></span>(O<span class="inline-formula"><sub>3</sub></span>)<span class="inline-formula"><sub>net</sub></span> measured here can be regarded as the lower limit of the real <span class="inline-formula"><i>P</i></span>(O<span class="inline-formula"><sub>3</sub></span>)<span class="inline-formula"><sub>net</sub></span> in the atmosphere; however, the measured <span class="inline-formula"><i>P</i></span>(O<span class="inline-formula"><sub>3</sub></span>)<span class="inline-formula"><sub>net</sub></span> was still <span class="inline-formula">∼</span> 7.5 to 9.3 ppbv h<span class="inline-formula"><sup>−1</sup></span> higher than the modeled <span class="inline-formula"><i>P</i></span>(O<span class="inline-formula"><sub>3</sub></span>)<span class="inline-formula"><sub>net</sub></span> value depending on different modeling methods, which may be due to the inaccurate estimation of HO<span class="inline-formula"><sub>2</sub></span> <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M43" display="inline" overflow="scroll" dspmath="mathml"><mo>/</mo></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="8pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="38128a0aedc95cb5017766f863958541"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-23-9891-2023-ie00001.svg" width="8pt" height="14pt" src="acp-23-9891-2023-ie00001.png"/></svg:svg></span></span> RO<span class="inline-formula"><sub>2</sub></span> radicals in the modeling study. Short-lived intermediate measurements coupled with direct <span class="inline-formula"><i>P</i></span>(O<span class="inline-formula"><sub>3</sub></span>)<span class="inline-formula"><sub>net</sub></span> measurements are needed in the future to better understand O<span class="inline-formula"><sub>3</sub></span> photochemistry. Our results show that the NPOPR detection system can achieve high temporal resolution and continuous field observations, which helps us to better understand photochemical O<span class="inline-formula"><sub>3</sub></span> formation and provides a key scientific basis for continuous improvement of air quality in China.</p>