Rapid formation of acetaldehyde and its influence on ozone formation in a petrochemical industrialized region

Acetaldehyde plays a significant role in atmospheric photochemical reactions and ozone formation. Previous studies have shown that acetaldehyde may rapidly be generated over short periods and impact ozone production, yet the underlying mechanism remains unclear. To better elucidate these mechanisms, a field campaign was conducted in Dongying, a typical petrochemical city in China. The observed acetaldehyde concentration averaged 3.0 ± 1.6 ppbv, with a peak around 09:00 local time. The diurnal variations of acetaldehyde were categorized into two types, with Category 1 exhibiting relatively high values and increasing sharply in concentration between 07:00 and 09:00 a.m. (refer to morning peak episode, MPE), and the remaining classified as Category 2. Category 1 was similar to previous studies at heavily polluted sites but differed from cleaner locations. Using an observation-based chemical box model, we found that acetaldehyde contributed an average of 10.2 % to the net ozone production rate. Combined with a positive matrix factorization model, we identified secondary formation as the dominant source of acetaldehyde (45.0 %), and the daytime production rate of acetaldehyde in Category 1 was significantly higher than that in Category 2. Cis-2-butene and trans-2-butene were identified as key precursors for the rapid acetaldehyde formation during the MEP, with the petroleum industry being their primary source. Volatile organic compounds (VOCs) from petroleum industry contributed over 60 % to acetaldehyde formation during the morning peak. Our findings underscore the urgent need for targeted VOCs management strategies in petroleum sector to mitigate both carbonyl and ozone formation.