Baozhu Ge

Impact of the regional transport of urban Beijing pollutants on downwind areas in summer: ozone production efficiency analysis

ABSTRACT Ambient measurements of SO2, O3, NO x , NO y and CO were made at Shangdianzi (SDZ), a rural site in the northeast (NE) of Beijing, and urban Beijing (China Meteorological Administration) from 1 June 2008 to 31 August 2008. The pollutants at SDZ showed very different levels under different wind conditions, with the levels under the southwest (SW) wind being much higher than those under the NE wind. The SW wind facilitates the transport of urban plume to SDZ, whereas the NE wind provides a background condition. At SDZ, the Ozone (O3) concentration in air masses from urban Beijing was found to be 33.4 ± 0.4 ppbv higher than that from clean regions in summer. The ozone production efficiency (OPE x ) for the urban plume and background condition was 4.0 and 5.3, respectively. Based on these OPE x values and the NO z values for the respective conditions, the contribution of in-situ production in the urban plume to the level of O3 at SDZ is estimated to be 8.6 ppbv, corresponding only to 25.7% of the total impact of urban plume transport. This suggests that direct transport of O3 rather than in-situ photochemistry contributes mainly to the summer elevation of the level of O3 at SDZ.

Wet deposition of acidifying substances in different regions of China and the rest of East Asia: modeling with updated NAQPMS.

The traditional way to study Sources-Receptor Relationships (SRRs) of wet deposition is based on sensitivity simulation, which has weakness in dealing with the non-linear secondary formation pollutants (e.g. ozone and nitrate). An on-line source tracking method has been developed in the Nested Air Quality Prediction Modeling System (NAQPMS) coupled with cloud-process module for the first time. The new model can not only quantify the total volume of the sulfate, nitrate and ammonium wet deposition with more accuracy, but also trace these acidic species to their emitted precursors. Compared with previous studies, our result clearly shows: (1) East China and Central China, which are the two primary export regions, have 15-30% and 10% effect on wet deposition in other areas, respectively; (2) Besides the above two regions, the total acid deposition in Southwestern and Northeastern China have reached or exceeded the critical loads under their own environmental conditions.

Modeling study of source contributions and emergency control effects during a severe haze episode over the Beijing-Tianjin-Hebei area

In February 2014, the Beijing-Tianjin-Hebei (BTH) area experienced a weeklong episode of heavy haze pollution. Cities such as Beijing (BJ) and Shijiazhuang (SJZ) issued heavy pollution alerts for the first time and took emergency control measures. This study employed the Nested Air Quality Prediction Modeling System (NAQPMS) to simulate and analyze the three-dimensional structure of the source contributions of PM2.5 in the BTH area during this pollution episode and quantitatively assessed the effects of the emergency control measures. The results showed that during the polluted period (February 19–26), surface PM2.5 mainly originated from local sources (48%–72%). In the entire BTH area, southern Hebei (SHB) represented the largest internal contribution (33%), while the main external contributions came from Shandong (SD) (10%) and Henan (HN) (4%). Vertically, the local contribution was constrained below the near-ground layer, and rapidly decreased with altitude. The regional transport path from SHB and Shanxi (SX) to BJ appeared at 0.5–1.5 and 1.5–2.5 km, with contributions of 32%–42% and 13%–27%, respectively. The non-local source regions for the BTH area were SD below 1 km and mainly SX and HN above 1 km. Compared to the non-polluted period (February 27–28), the contribution from regional transport increased during the polluted period, indicating the key role of regional transport in the pollution formation. The emergency control measures had a relatively large effect on NOx and SO2 concentrations, but a limited effect on PM2.5. The stronger regional transport during the polluted period may have weakened the effects of the local emergency control measures. These results indicated that a coordinated emission control should be implemented not only over the BTH area but also over its surrounding provinces (e.g. SD, HN).

Investigating the evolution of summertime secondary atmospheric pollutants in urban Beijing.

Understanding the formation of tropospheric ozone (O3) and secondary particulates is essential for controlling secondary pollution in megacities. Intensive observations were conducted to investigate the evolution of O3, nitrate (NO3-), sulfate (SO42-) and oxygenated organic aerosols ((OOAs), a proxy for secondary organic aerosols) and the interactions between O3, NOx oxidation products (NOz) and OOA in urban Beijing in August 2012. The O3 concentrations exhibited similar variations at both the urban and urban background sites in Beijing. Regarding the O3 profile, the O3 concentrations increased with increasing altitude. The peaks in O3 on the days exceeding the 1h or 8h O3 standards (polluted days) were substantially wider than those on normal days. Significant increases in the NOz mixing ratio (i.e., NOy - NOx) were observed between the morning and early afternoon, which were consistent with the increasing oxidant level. A discernable NO3- peak was also observed in the morning on the polluted days, and this peak was attributed to vertical mixing and strong photochemical production. In addition, a SO42- peak at 18:00 was likely caused by a combination of local generation and regional transport. The OOA concentration cycle exhibited two peaks at approximately 10:00 and 19:00. The OOA concentrations were correlated well with SO42- ([OOA]=0.55×[SO42-]+2.1, r2=0.69) because they both originated from secondary transformations that were dependent on the ambient oxidization level and relative humidity. However, the slope between OOA and SO42- was only 0.35, which was smaller than the slope observed for all of the OOA and SO42- data, when the RH ranged from 40 to 50%. In addition, a photochemical episode was selected for analysis. The results showed that regional transport played an important role in the evolution of the investigated secondary pollutants. The measured OOA and Ox concentrations were well correlated at the daily scale, whereas the hourly OOA and Ox concentrations were insignificantly correlated in urban Beijing. The synoptic situation and the differences in the VOC oxidation contributing to O3 and SOAs may have resulted in the differences among the correlations between OOA and Ox at different time scale. We calculated OOA production rates using the photochemical age (defined as -log10(NOx/NOy)) in urban plumes. The CO-normalized OOA concentration increased with increasing photochemical age, with production rates ranging from 1.1 to 8.5μgm-3ppm-1h-1 for the plume from the NCP.

Simulation on different response characteristics of aerosol particle number concentration and mass concentration to emission changes over mainland China

In this study, Nested Air Quality Prediction Modeling System with Advance Particle Microphysics module (NAQPMS+APM) is applied to simulate the response characteristics of aerosol particle number concentration and mass concentration to emission changes over mainland China. It is the first attempt to investigate the response of both aerosol mass concentration and number concentration to emission changes using a chemical transport model with detailed aerosol microphysics over mainland China. Results indicate that the response characteristics are obviously different between aerosol particle number concentration and mass concentration. Generally, the response of number concentration shows a more heterogeneous spatial distribution than that of mass concentration. Furthermore, number concentration has a higher sensitivity not only to primary particles emission but also to precursor gases than that of mass concentration. Aerosol particle mass concentration exhibits a consistent trend with the emission change and yet aerosol number concentration does not. Due to the nonlinearity of aerosol microphysical processes, reduction of primary particles emission does not necessarily lead to an obvious decrease of aerosol number concentration and it even increases the aerosol number concentration. Over Central-Eastern China (CEC), the most polluted regions in China, reducing primary particles emission rather than precursor gas emissions is more effective in reducing particles number concentration. By contrast, the opposite is true over the northwestern China. The features of fine particles pollution revealed in this study are associated with the spatial differences in Chinas population, geography, climate and economy. Considering the more adverse effects of ultrafine particles on human health and the spatial distribution of population, making different measures in controlling particles number concentration from that controlling mass concentration in different regions over mainland China is indicated. MAIN FINDINGS FPN concentration responds more heterogeneously to emission than FPM. Spatial difference of response of FPN to emission is distinguished by a boundary line.

Synergistic effect of water-soluble species and relative humidity on morphological changes of aerosol particles in Beijing mega-city during severe pollution episodes

Depolarization ratio (δ) of backscattered light from aerosol particle is an applicable parameter for real-time 18 distinguishing spherical and non-spherical particles, which has been widely adopted by ground-based Lidar observation and 19 satellite remote sensing. From November 2016 to February of 2017, it consecutively suffered from numbers of severe air 20 pollution at Beijing with daily averaged mass concentration of PM2.5 (aerodynamic diameter less than 2.5μm) larger than 150 21 μg/m. We preformed concurrent measurements of water-soluble chemical species and depolarization properties of aerosol 22 particles on the basis of a continuous dichotomous Aerosol Chemical Speciation Analyzer (ACSA-14) and a bench-top optical 23 particle counter with a polarization detection module (POPC). We found that δ value of ambient particles generally decrease 24 as mass concentration of PM2.5 increased at unfavorable meteorological condition. Ratio of mass concentration of nitrate 25 (NO3) to that of sulfate (SO4) in PM2.5 was 1.5 ± 0.6, indicating of great importance of NOx in the formation of heavy 26 pollution. Mass concentration of NO3 in PM2.5 (fNO3) was generally an order of magnitude higher than that in coarse mode 27 Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2018-623 Manuscript under review for journal Atmos. Chem. Phys. Discussion started: 2 August 2018 c