Biogenic isoprene in subtropical urban settings and implications for air quality

The ratios of isoprene to 1,3-butadiene, an exhaust tracer, were used to estimate the fractions of biogenic and anthropogenic isoprene in the urban area. The results reveal that the biogenic contribution apparently overwhelmed the anthropogenic contribution in summertime, although traffic in the city is heavy. Furthermore, the residual isoprene (mostly biogenic) after daytime photochemical loss persisted into the nighttime and contributed a large fraction to nighttime isoprene. In autumn, daytime isoprene was also predominantly from biogenic sources because the hot and sunny conditions persist into the autumn months. The high biogenic isoprene levels in subtropical urban settings and its coherence with OH diurnal cycles accentuate the significance of biogenic isoprene and its potentially great impact on atmospheric oxidant capacity, urban air quality, and even regional climate.