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Ozone and its precursors were measured from 15 June 2006 to 14 June 2007 at an urban site in Shanghai and used to characterize photochemical oxidant production in this region. During the observation period, ozone displays a seasonal variation with a maximum in spring. Observed nitrogen oxides (NOx) and carbon monoxide (CO) reached a maximum in winter and a minimum in summer. NOx and CO has a similar double-peak diurnal cycle, implying that they are largely of motor vehicle origin. Total nonmethane organic compounds (NMOC) concentrations averaged over the morning, and the 24-hour periods have a large day-to-day variation with no apparent seasonal cycle. Aromatics play a dominant role in contributing to total NMOC reactivity and ozone-forming potential. Anthropogenic NMOC of diverse sources are major components of total NMOC and consist mainly of moderate and low reactivity species. In contrast, relatively low levels of biogenic NMOC concentrations were observed in urban Shanghai. The early morning NMOC/NOx ratios are typically below 8:1 with an average of around 4:1, indicating that the sampling location is situated in a NMOC-limited regime. Model simulations confirm that potential photochemical ozone production in Shanghai is NMOC-sensitive. It is presently difficult to predict the impact of future human activities, such as the increase of automobiles and vegetation-covered landscapes and the reduction of aerosol on ozone pollution in the fast developing megacities of China, and additional studies are needed to better understand the highly nonlinear ozone problem. © 2009., the American Geophysical Union.

In this study, a regional dynamical model (WRF) is used to drive biogenic emission models to calculate high resolution (10x10 km) biogenic emissions of isoprene (C(5)H(8)), monoterpenes (C(10)H(16)), and nitric oxide (NO) in China. This high resolution biogenic inventory will be available for the community to study the effect of biogenic emissions on photochemical oxidants in China. The biogenic emissions are compared to anthropogenic emissions to gain insight on the potential impact of the biogenic emissions on tropospheric chemistry, especially ozone production in this region. The results show that the biogenic emissions in China exhibit strongly diurnal, seasonal, and spatial variations. The isoprenoid (including both isoprene and monoterpenes) emissions are closely correlated to tree density and strongly vary with season and local time. During winter (January), the biogenic isoprenoid emissions are the lowest, resulting from lower temperature and solar radiation, and highest in summer (July) due to higher temperature and solar radiation. The biogenic NO emissions are also higher during summer and lower during winter, but the magnitude of the seasonal variation is smaller than the emissions of isoprene and monoterpenes. The biogenic emissions of NO are widely spread out in the northern, eastern, and southern China regions, where high-density agricultural soil lands are located. Both biogenic NO and isoprenoid emissions are very small in western China. The calculated total biogenic emission budget is smaller than the total anthropogenic VOC emission budget in China. The biogenic isoprenoid and anthropogenic VOC emissions are 10.9 and 15.1 Tg year(-1), respectively. The total biogenic and anthropogenic emissions of NO are 5.9 and 11.5 Tg(NO) year(-1), respectively. The study shows that in central eastern China, the estimated biogenic emissions of isoprenoids are very small, and the anthropogenic emissions of VOCs are dominant in this region. However, in northeastern and southern China, there are relatively large biogenic emissions of isoprenoids, leading to an important impact on the ozone production in these regions. Furthermore, the emissions of isoprenoids are highest during summer and noontime, which correlates to the peak of ozone production period. For example, the ratio between summer and winter for the emissions of isoprenoids is about 15 in China. As a result, the biogenic emissions of isoprenoids are significantly larger than the anthropogenic emissions of VOCs in China during daytime in summer. Biogenic NO emissions are mostly produced by agricultural soils which co-exist with large populations and human activity. As a result, the biogenic emissions of NO are mostly overlapped with the anthropogenic emissions of NO, leading to the enhancement in NO concentrations in the high anthropogenic NO emission regions. Finally, the future emissions of isoprene and monoterpenes over China are estimated. The results show that the future biogenic emissions may increase significantly due to land cover changes in central eastern China, which could have a very important impact on ozone formation in this region. However, these estimates are highly uncertain and are presented as a potential scenario to show the importance of possible changes of biogenic emissions in China.

Isoprene is emitted from vegetation to the atmosphere in significant quantities, and it plays an important role in the reactions that control tropospheric oxidant concentrations. As future climatic and land-cover changes occur, the spatial and temporal variations, as well as the magnitude of these biogenic isoprene emissions, are expected to change. This paper presents a study of the change in biogenic isoprene emissions that would result from both anthropogenic land-cover and climate-driven changes. Annual global isoprene emissions were estimated to be 522 Tg yr-1 under current climatological and land-cover conditions. When climate-driven land-cover changes are predicted, but climate does not change, total global emissions did not change significantly, although regional impacts were important. However, the use of future temperature and land-cover drivers to estimate isoprene emissions produced a global estimate of 889 Tg yr-1. Anthropogenic land-cover changes, such as urbanization and changes of natural vegetation to plantation forests, can also have substantial impacts on isoprene emissions (i.e., up to 717 Tg yr-1, a 37% increase, when land-cover changes but temperature remains at current-day values). The Model for Ozone and Related Tracers, version 2 (MOZART-2) was run with the different isoprene emission scenarios to simulate the potential changes in global atmospheric chemical composition. The simulated regional surface ozone concentrations changed as much as -9 to 55 ppbv under certain emission and climate scenarios. These results were used to evaluate changes in the ozone production chemistry under different emission scenarios. As expected, the impacts of changing isoprene emissions are regionally dependent, with large changes in China, the Amazon, and the United States.

We use a global chemical transport model (MOZART-2) to estimate the effects of surface emissions of methanol on tropospheric oxidants. The importance of methanol in tropospheric chemistry is two fold. First, methanol has a relatively large surface emission with an estimated global emission of 70 to 350 Tg methanol/year. The estimated methanol flux is comparable to other major hydrocarbon surface emissions such as isoprene and total monoterpenes, but the chemical lifetime of methanol is several days (in the boundary layer) to a few weeks (in the upper troposphere), which is much longer than the chemical lifetime of isoprene or monoterpenes (For example, the chemical lifetime of isoprene is about 2 hours). With a surface emission of 104 to 312 Tg methanol/year (encompasses estimated uncertainty in methanol emissions), the calculation shows that on average, the inclusion of methanol emission produces approximately 1-2% increase in O3, 1-3% decrease in OH, 3-5% increase in HO2, and 3-9% increase in CH2O globally. The maximum perturbation to the oxidants occurs in the tropical upper troposphere. However, the uncertainty associated with current methanol emission estimates produces significantly different model predictions of tropospheric oxidant distributions.

Changes in land use and land cover (LULC) influence meteorological fields and biogenic emissions, further affecting the atmospheric chemistry and air quality. Combining the satellite measurements and WRF‐Chem model simulations, we evaluate the impacts of the LULC change between 2001 and 2018 on the summertime ozone (O3) formation in North China Plain and surrounding areas (NCPs). Satellite measurements have revealed that from Taihang to Yanshan Mountain, the fraction of broadleaf and needle forest coverage has increased by 5%–20% and the urban area has increased by up to 25% in the NCP. Additionally, the vegetation density has increased significantly in the NCPs except for urban areas. The LULC change generally enhances biogenic volatile compounds emissions in the NCPs, particularly over Taihang and Yanshan mountain, but the O3 variation is divergent. The maximum daily 8‐ihr average (MDA8) O3 concentrations are reduced by 1%–7% over Taihang and Yanshan Mountain because the raised vegetation density increases O3 dry deposition velocity to accelerate the O3 loss. The raised vegetation density enhances the evapotranspiration to decrease the near‐surface temperature by 0.1°C–1.5°C, which also generates a divergence in the low‐level atmosphere in the NCPs, causing secondary northerly or easterly winds in the NCP. The O3 enhancement along the coastal areas of the NCP is attributed to the perturbation of wind fields and photolysis induced by the LULC change. The divergent variation of the MDA8 O3 concentrations in the NCP is generally caused by the variations of biogenic emissions and photolysis. Plain Language Summary: Changes in land use and land cover (LULC) impact meteorological fields, biogenic emissions, atmospheric chemistry, and air quality. We estimate impacts of LULC changes between 2001 and 2018 on summertime ozone (O3) formation in the North China Plain and surrounding areas (NCPs) using satellite measurements and WRF‐Chem model simulations. Satellite measurements have shown a 5%–20% increase in the fraction of broadleaf and needle forest coverage from the Taihang Mountain to the Yanshan Mountain and an increase of up to 25% in urban areas of the NCP. Moreover, the vegetation density in the NCP has increased significantly except for urban areas. LULC changes generally enhance biogenic volatile compound emissions in the NCPs, especially over Taihang and Yanshan Mountain, but the O3 variation is divergent. Because the increased vegetation density raises the O3 dry deposition velocity and accelerates O3 loss, the maximum daily 8‐hr average (MDA8) O3 concentrations over Taihang and Yanshan Mountain are reduced by 1%–7%. The O3 increase along the coastal areas of the NCP is attributable to perpetuations in wind fields and photolysis induced by LULC change. In general, variations in biogenic emissions and photolysis are responsible for the divergent variation of MDA8 O3 concentrations in the NCP. Key Points: The increased vegetation density enhances biogenic volatile compounds emissions in North China Plain and surrounding areas (NCPs)Increased O3 dry deposition velocity is one of the most possible reasons for the O3 loss in the areas with the raised vegetation densityThe divergent variation of the O3 concentration is caused by variations of meteorological fields, biogenic volatile organic compounds and photolysis [ABSTRACT FROM AUTHOR]