ALBERT

Description: The Beijing area has suffered from severe air pollution in recent years, including ozone pollution in the summer. In addition to the anthropogenic emissions inventory, understanding local ozone pollution requires a reliable biogenic volatile organic compound (BVOC) emission inventory. Forest coverage rose from 20.6 to 35.8 % from 1998 to 2013 in Beijing according to the National Forest Resource Survey (NFRS), and accurate representations of land cover for recent years is crucial for estimating BVOC emissions and their impacts on air quality. In this study, we established a high-resolution BVOC emission inventory in Beijing using the Model of Emissions of Gases and Aerosols from Nature (MEGAN) v2.1 with three independent leaf area index (LAI) products and three independent land cover products. Various combinations of the Global LAnd Surface Satellite (GLASS), Moderate-Resolution Imaging Spectroradiometer (MODIS) MCD15, and GEOland (GEO) v2 LAI datasets and the Finer Resolution Observation and Monitoring of Global Land Cover (FROM-GLC), MODIS MCD12Q1 plant functional type (PFT) products, and Climate Change Initiative Land Cover (CCI LC) products are used in five model sensitivity experiments (E1–E5), and the experiment using the FROM-GLC with the highest spatial resolution of 30 m and GLASS LAI products was treated as the baseline. These sensitivity calculations were driven by hourly, 3 km meteorological fields from the Weather Research and Forecasting (WRF) model. The following results were obtained: (1) according to the baseline estimate, the total amount of BVOC emissions is 75.9 Gg for the Beijing area, and isoprene, monoterpenes, sesquiterpenes and other VOCs account for 37.6, 14.6, 1.8 and 46 % of the total, respectively. Approximately three-quarters of BVOC emissions occur in the summer. (2) According to the sensitivity experiments, the LAI input does not significantly affect the BVOC emissions. Using MODIS MCD15Q1 and GEO v2 LAI led to slight declines of 2.6 and 1.4 %, respectively, of BVOC emissions in the same area. (3) The spatial distribution of PFTs from different inputs strongly influenced the spatial distribution of BVOC emissions. Furthermore, the cross-walking table for converting land cover classes to PFTs also has a strong impact on BVOC emissions; the sensitivity experiments showed that the estimate of BVOC emissions by CCI LC ranged from 42.1 to 70.2 Gg depending on the cross-walking table used.

Description: The Atmospheric Pollution and Human Health in a Chinese Megacity (APHH-Beijing) programme is an international collaborative project focusing on understanding the sources, processes and health effects of air pollution in the Beijing megacity. APHH-Beijing brings together leading China and UK research groups, state-of-the-art infrastructure and air quality models to work on four research themes: (1) sources and emissions of air pollutants; (2) atmospheric processes affecting urban air pollution; (3) air pollution exposure and health impacts; and (4) interventions and solutions. Themes 1 and 2 are closely integrated and support Theme 3, while Themes 1–3 provide scientific data for Theme 4 to develop cost-effective air pollution mitigation solutions. This paper provides an introduction to (i) the rationale of the APHH-Beijing programme and (ii) the measurement and modelling activities performed as part of it. In addition, this paper introduces the meteorology and air quality conditions during two joint intensive field campaigns – a core integration activity in APHH-Beijing. The coordinated campaigns provided observations of the atmospheric chemistry and physics at two sites: (i) the Institute of Atmospheric Physics in central Beijing and (ii) Pinggu in rural Beijing during 10 November–10 December 2016 (winter) and 21 May–22 June 2017 (summer). The campaigns were complemented by numerical modelling and automatic air quality and low-cost sensor observations in the Beijing megacity. In summary, the paper provides background information on the APHH-Beijing programme and sets the scene for more focused papers addressing specific aspects, processes and effects of air pollution in Beijing.

Description: The Beijing area has suffered from severe air quality pollution in recent years, including ozone pollution in the summer. Except for the anthropogenic emissions inventory, understanding the local ozone pollution still requires the reliable biogenic emission inventory. The forest coverage rate rose from 20.6 % to 35.8 % during 1998–2013 in Beijing according to the National Forest Resource Survey (NFRS). In this study, we established a new high resolution biogenic volatile organic compounds (BVOCs) emission inventory in Beijing based on Model of Emission of Gases and Aerosols from Nature (MEGAN) v2.1 model with three independent leaf area index (LAI) products and three independent land cover products. The Global LAnd Surface Satellite (GLASS) LAI, Moderate-Resolution Imaging Spectroradiometer (MODIS) MCD15 LAI, GEOland (GEO) v2 LAI datasets, and the Finer Resolution Observation and Monitoring of Global Land Cover (FROM-GLC), MODIS MCD12Q1 PFT products and Climate Change Initiative Land Cover (CCI-LC) products are used to design five experiments, as E1-E5, to calculate and test the sensitivity of the model. Based on the meteorological conditions from Weather Forecasting and Research (WRF) model, this inventory is an hourly inventory with 3-km spatial resolution. The result shows: (1) According to the baseline estimation, the total amount of BVOCs emissions are 99.9 Gg for Beijing area. The estimated annual emissions of isoprene, monoterpenes, sesquiterpenes and other VOCs are 52.5 Gg, 11.1 Gg, 1.4 Gg and 34.9 Gg, respectively. (2) The BVOCs emissions have the significant seasonal variability, which the summer season contributes 76.6 % of the total BVOCs emissions in Beijing, and the winter season only contributes 0.3 % emissions due to the low temperature and near-zero biomass of deciduous trees. (3) The broadleaf tree, as the dominant contributor to the BVOCs emissions, accounts for 94.5 % isoprene, 53.3 % monoterpenes, 53.8 % sesquiterpenes and 34.1 % other VOCs. (4) The MODIS LAI lead to a 17.4 % decline in BVOCs emissions because of the large mask area near the urban and water area. However, the GEO and GLASS LAI only led to a 1.0 % difference of total BVOCs emissions even with different temporal updating frequency of LAI. (5) The difference of PFTs have an obvious effect on the spatial distribution and density of BVOCs emissions. The MODIS and CCI-LC land cover led to an approximate 5.0 % and 26.0 % decline in BVOCs emissions compared with the baseline estimation. (6) The estimation of local BVOCs emissions in this study is much higher than the previous studies, and the development of local forest is main reason led to such the difference, thus implying that previous estimation of BVOCs in Beijing is underestimated and is not suitable for the current scene. In addition, further study will investigate and evaluate the effect of BVOCs on the local atmospheric environment through the regional chemistry transport model.

Description: APHH-Beijing (Atmospheric Pollution and Human Health in a Chinese Megacity) is an international collaborative project to examine the emissions, processes and health effects of air pollution in Beijing. The four research themes of APHH-China are: (1) sources and emissions of urban atmospheric pollution; (2) processes affecting urban atmospheric pollution; (3) exposure science and impacts on health; and (4) interventions and solutions to reduce health impacts. Themes 1 and 2 are closely integrated and support Theme 3, while Themes 1–3 provide scientific data for Theme 4 on the development of cost-effective solutions. A key activity within APHH-Beijing was the two month-long intensive field campaigns at two sites: (i) central Beijing, and (ii) rural Pinggu. The coordinated campaigns provided observations of the atmospheric chemistry and physics in and around Beijing during November–December 2016 and May–June 2017. The campaigns were complemented by numerical air quality modelling and air quality and meteorology data at the 12 national monitoring stations in Beijing. This introduction paper provides an overview of (i) APHH-Beijing programme, (ii) the measurement and modelling activities performed as part of it in Beijing, and (iii) the air quality and meteorological conditions during the two field campaigns. The winter campaign was characterized by high PM2.5 pollution events whereas the summer experienced high ozone pollution events. Air quality was poor during the winter campaign, but less severe than in the same period in 2015 when there were a number of major pollution episodes. PM2.5 levels were relatively low during the summer period, matching the cleanest periods over the previous five years. Synoptic scale meteorological analysis suggests that the greater stagnation and weak southerly circulation in November/December 2016 may have contributed to the poor air quality.