Vegetation provides a major source of reactive carbon entering the atmosphere. These compounds play an important role in (1) shaping global tropospheric chemistry, (2) regional photochemical oxidant formation, (3) balancing the global carbon cycle, and (4) production of organic acids which contribute to acidic deposition in rural areas. Present estimates place the total annual global emission of these compounds between approximately 500 and 825 Tg yr−1. The volatile olefinic compounds, such as isoprene and the monoterpenes, are thought to constitute the bulk of these emissions. However, it is becoming increasingly clear that a variety of partially oxidized hydrocarbons, principally alcohols, are also emitted. The available information concerning the terrestrial vegetation as sources of volatile organic compounds is reviewed. The biochemical processes associated with these emissions of the compounds and the atmospheric chemistry of the emitted compounds are discussed.

Non‐methane hydrocarbons (NMHCs) play very important roles in atmospheric chemistry, yet little is known about their abundance in the atmosphere of China, especially in the background atmospheres. Measurements of C2‐C10 NMHCs were concurrently carried out at two remote background sites and one rural background site in April and May 2004 in this study: Tengchong Mountain (TM) in Yunnan province on the border of southwestern China; Jianfeng Mountain (JM) on the southwest coast of Hainan Island, southern China; and Lin'an (LA) in Zhejiang province in eastern China. Additional samples were collected at an urban site, Tengyue Town (TT, about 10 km from TM), to obtain local urban NMHC profiles. NMHC levels in these background sites were compared with other rural and remote sites in Asia and other global background stations. In the urban site of TT, local biofuel combustion was the major contributor to the high levels of ethene, ethyne, and ethane. In LA, the major sources of NMHCs were the emissions from fossil fuel and biofuel combustion and from industrial solvent use. Compared with another study conducted in 2001, toluene levels had increased by 75% in 2004 in this study, whereas the levels of other anthropogenic hydrocarbons remained at the same levels. Local industrial emissions and transports from the Yangtze River Delta were the major sources of toluene, ethylbenzene, and xylenes in LA. While in TM, the major sources were regional biofuel combustions and biomass burning emissions from Southeast Asia. Long‐range transport of air masses from Southeast Asia was the major source of NMHCs in JM in spring. JM showed the lowest levels of most hydrocarbons among the three background sites. Several hydrocarbon molar ratios, such as benzene/toluene and ethane/propane, were used to characterize the signatures of air masses from different regions.

No abstract

An intensive campaign for atmospheric pollution was carried out from October to November 2004 in Pearl River Delta Region (PRDR) of China in order to better understand the dominative factors for controlling air quality and impacts of pollutants on the regional environment. The object of this study aimed to investigate the characters and sources of particulates through the study of chemical compositions in different wind pattern in Guangzhou city. The ambient concentrations of mass, soluble species, and carbonaceous matter in PM 2.5 particulates with time resolutions of 15 minutes, 15 minutes, and 12 hours were measured by TEOM, in-situ IC system, and carbon analyzer, respectively. During the sampling time, high concentrations of PM 2.5 mass and its chemical compositions were found, which was comparable or higher than other measurements in mainland China. The average SO 4 2-, NH 4 + , and NO 3 -concentrations were 38.6, 13.6, and 8.8 μg/m 3 , which accounted for 26.5%, 13.6%, and 5.7% of the total particulate mass, respectively. In the frontal system, biomass burning was the significant emission source and the great amount of SO 4 2-and NH 4 + particulates were observed in the aged secondary particulates, together with the dry prevailing northerly wind. In the local system, low value of sulfur oxidation ratio and high correlation coefficient between sulfate and elemental carbon were also observed under the prevailing southeasterly wind. It could be explained that the heterogeneous reaction of sulfate on soot particles causes high levels of NO x in Guangzhou. Great amount of SO 2 would further convert to secondary sulfate particles through photochemical reactions during transport to the inner areas, which will cause more serious air pollutions in the southern China.

<p><strong>Abstract.</strong> To investigate the atmospheric oxidizing capacity in certain polluted isoprene-rich environments, such as the forests surrounding megacities. Here we present online observations of isoprene and its first-stage oxidation products methyl vinyl ketone (MVK) and methacrolein (MACR) in summer 2016 at a remote, high-altitude mountain forest site (1690 m a.s.l.) to the north of the air-polluted Pearl River Delta (PRD) region in southern China. The observed isoprene level was found to be significantly lower in comparison with other forest sites either in China or around the world, although the sampling site was surrounded with subtropical evergreen broad-leaved trees which are strong isoprene emitters. Also, high (MVK+MACR)/isoprene ratio was observed. Based on the observations, we hypothesized that the lower isoprene levels in the study forest might be attributable to a strong atmospheric oxidative capacity in relation to the elevated regional complex air pollution. High daytime OH and nighttime NO<sub>3</sub> radical concentrations estimated by using a photochemical box model incorporating Master Chemical Mechanism (PBM-MCM), as well as calculated short atmospheric reaction times of isoprene and long photochemical age, indicated that the isoprene was rapidly and fully oxidized at this aged atmospheric environment, which confirmed our hypothesis. The study suggests that the complex air pollution in the PRD region has significantly elevated the background atmospheric oxidative capacity of the adjacent forests, and most likely does would probably affect the regional air quality and ecological environment in the long term. The feedback of forest ecosystems to the increasing atmospheric oxidation capacity warrants further studies.</p>