Comment on acp-2022-399

<strong class="journal-contentHeaderColor">Abstract.</strong> Comprehensive aircraft measurements of volatile organic compounds (VOCs) covering the South Coast Air Basin (SoCAB) and San Joaquin Valley (SJV) of California were obtained in the summer of 2019. Combined with the CO, CH<span class="inline-formula">₄</span>, and NO<span class="inline-formula">_<i>x</i></span> data, the total calculated gas-phase hydroxyl radical reactivity (cOHR<span class="inline-formula">_TOTAL</span>) was quantified to be 6.1 and 4.6 s<span class="inline-formula">^−1</span> for the SoCAB and SJV, respectively. VOCs accounted for <span class="inline-formula">∼</span> 60 %–70 % of the cOHR<span class="inline-formula">_TOTAL</span> in both basins. In particular, oxygenated VOCs (OVOCs) contributed <span class="inline-formula"><i>&gt;</i>60</span> % of the cOHR of total VOCs (cOHR<span class="inline-formula">_VOC</span>) and the total observed VOC mixing ratio. Primary biogenic VOCs (BVOCs) represented a minor fraction (<span class="inline-formula"><i>&lt;</i>2</span> %) of the total VOC mixing ratio but accounted for 21 % and 6 % of the cOHR<span class="inline-formula">_VOC</span> in the SoCAB and SJV, respectively. Furthermore, the contribution of BVOCs to the cOHR<span class="inline-formula">_VOC</span> increased with increasing cOHR<span class="inline-formula">_VOC</span> in the SoCAB, suggesting that BVOCs were important ozone precursors during high ozone episodes. Spatially, the trace gases were heterogeneously distributed in the SoCAB, with their mixing ratios and cOHR being significantly greater over the inland regions than the coast, while their levels were more evenly distributed in SJV. The results highlight that a better grasp of the emission rates and sources of OVOCs and BVOCs is essential for a predictive understanding of the ozone abundance and distribution in California.