Seasonal characteristics of biogenic and anthropogenic isoprene in tropical–subtropical urban environments

Abstract

h i g h l i g h t sIsoprene in urban environments at tropicalesubtropical latitudes was studied. Seasonal and spatial differences in isoprene's levels and sources were investigated. A temperature kick-start threshold of isoprene emissions was clearly demonstrated. Such a threshold may vary with vegetation types and temperature zones. a b s t r a c tMeasurements of atmospheric isoprene and other selected volatile organic compounds (VOCs) were conducted in Taipei, a tropicalesubtropical metropolis, to investigate diurnal variations, seasonal diversity and spatial differences in terms of the levels and sources of isoprene. Our study also investigated the responses of biogenic isoprene to both light flux and temperature in real urban settings that have a variety of plant species and traffic volumes. The robust ratio of isoprene/1,3-butadiene obtained from pure traffic emissions was used as a gauge to separate biogenic isoprene from traffic emissions. The four seasonal measurements at a typical urban site in the city showed that biogenic contributions overwhelmed their anthropogenic counterparts in summer and dominated the daytime isoprene levels in spring and autumn. Even in winter, biogenic sources still contributed a non-negligible fraction of approximately 44% to daytime isoprene. Furthermore, the concentration contour of isoprene extrapolated from the data at 38 sites throughout the city revealed that high levels of biogenic isoprene were generally a widespread phenomenon in summer in the tropicalesubtropical city. A three-dimensional plot of the isoprene/1,3-butadiene ratio, ambient temperatures and radiation flux showed a temperature threshold of biogenic isoprene emissions, beyond which the biogenic contribution began to increase exponentially with enhanced ambient temperature. However, when the ambient temperature was below the threshold, there was no or negligible biogenic contribution to the ambient isoprene, regardless of the strength of the radiation flux. The temperature threshold (approximately 17e21 C) of isoprene emissions in the tropicalesubtropical city was much higher than the thresholds in cities and areas at temperate latitudes, indicating that the adaptation of vegetation to different temperature zones via isoprene emission may be characteristic.

Revelation of Coupling Biogenic with Anthropogenic Isoprene by Highly Time-Resolved Observations

“…Two-year worth of data from 2008 to 2010 for the Wanhua site were used for the study, which included approximately 5 × 10 5 data points. This highly temporally resolved dataset from a fixed site revealing very detailed features in variations of the PAMS species, including isoprene and ethylene, is hardly achievable by the flask sampling method (Wang et al, 2013;Chang et al, 2014).…”

“…Isoprene is a C 5 compound listed as one of the 54 PAMS species analyzed on the hourly basis by the PAMS network. Although 1, 3-butadiene was commonly used as the indicator of vehicular emissions in an urban setting to separate the contributions of biogenic vs anthropogenic sources (Reimann et al, 2000;Borbon et al, 2001;Wang et al, 2013;Chang et al, 2014), it was not targeted by the PAMS list of the 54 target compounds. Instead, ethylene was used as the surrogate of vehicular source (McLaren et al, 1996;Reimann et al, 2000;Borbon et al, 2001) (See Fig.…”

“…Although studies of isoprene with in-situ measurements made in the temperate zones were sufficiently extensive and thorough (Borbon et al, 2001;von Schneidemesser et al, 2011;Hellén et al, 2012), vegetation and climate in other latitudinal zones are known to be significantly different, making direct adoption of the temperate findings to subtropical or tropical climates prone to errors. In the past, flask samples were collected in a major city of subtropical climate and found dramatic seasonal/ diurnal variations and high temporal variability of terrestrial dependence (Wang et al, 2013;Chang et al, 2014). Although flask sampling can provide the general knowledge of isoprene's abundance and variability in a given region, the on-site continuous monitoring of isoprene can complement flask sampling to provide better details of variability and longer time span in profiling isoprene's inter-annual variations with superb resolution.…”

“…To complement the flask sampling (Wang et al, 2013;Chang et al, 2014), which previously stressed more on spatial variability than temporal resolution, this study attempts to perform the opposite; that is to focus on the temporal variability of isoprene with superb resolution. Isoprene and other selected VOCs with hourly resolution were monitored in the same major metropolis of subtropical climate by an automated monitoring station.…”

Impact of isoprene and HONO chemistry on ozone and OVOC formation in a semirural South Korean forest

“…Despite the strong anthropogenic pollutant emissions in East Asia (China, Japan, and South Korea), recent research has shown that isoprene accounts for a major OH chemical sink in suburban areas near Beijing (Ran et al, 2011), the Pearl River Delta region , Taipei (Chang et al, 2014), and Seoul (Kim et al, 2013b;Kim et al, 2013). Consequently, modeling studies also clearly show that isoprene contributes significantly to ozone formation in Asian megacity regions.…”