Ozone pollution in China: A review of concentrations, meteorological influences, chemical precursors, and effects

Air quality is concerned with pollutants in both the gas phase and solid or liquid phases. The latter are referred to as aerosols, which are multifaceted agents affecting air quality, weather and climate through many mechanisms. Unlike gas pollutants, aerosols interact strongly with meteorological variables with the strongest interactions taking place in the planetary boundary layer (PBL). The PBL hosting the bulk of aerosols in the lower atmosphere is affected by aerosol radiative effects. Both aerosol scattering and absorption reduce the amount of solar radiation reaching the ground and thus reduce the sensible heat fluxes that drive the diurnal evolution of the PBL. Moreover, aerosols can increase atmospheric stability by inducing a temperature inversion as a result of both scattering and absorption of solar radiation, which suppresses dispersion of pollutants and leads to further increases in aerosol concentration in the lower PBL. Such positive feedback is especially strong during severe pollution events. Knowledge of the PBL is thus crucial for understanding the interactions between air pollution and meteorology. A key question is how the diurnal evolution of the PBL interacts with aerosols, especially in vertical directions, and affects air quality. We review the major advances in aerosol measurements, PBL processes and their interactions with each other through complex feedback mechanisms, and highlight the priorities for future studies.

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Aerosol and boundary-layer interactions and impact on air quality

http://www.klacp.ac.cn/kycg/scilw/201503/W020150320631940378413.pdf

Effects of meteorology and secondary particle formation on visibility during heavy haze events in Beijing, China

Analysis of land use/land cover change, population shift, and their effects on spatiotemporal patterns of urban heat islands in metropolitan Shanghai, China

Haze is a severe hazard that greatly influences traffic and daily life with great economic losses and threats to human health. To enhance understanding of the haze occurrences, this study examined the haze variations over North China and their associated atmospheric circulations for the period of 1960–2012 using daily visibility data. Results indicate that the haze events over this region primarily occur in boreal winter of year and mainly in the morning of day. The results of the analysis of the long-term variations indicate that the annual haze days were relatively few in the 1960s but increased steeply in the 1970s and have remained stable to the present. Some differences are obvious among seasons. A stably increasing trend is discernable in summer and autumn, relatively low in the 1960s and the 1990s–2000s and relatively high in the 1970s–1980s in spring and winter. Haze variations in urban regions are quite similar to haze variations in rural regions but with more haze days in urban regions because of the high aerosol emissions. Further analyses indicate that the occurrences of severe haze events in boreal winter generally correlate with the weakened northerly winds and the development of inversion anomalies in the lower troposphere, the weakened East Asian trough in the midtroposphere, and the northward East Asian jet in the high troposphere. All of these factors provide a favorable atmospheric background for the maintenance and development of haze events in this region.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2015JD023225

Haze Days in North China and the associated atmospheric circulations based on daily visibility data from 1960 to 2012

The continuous measurement of nitric oxide (NO), nitrogen dioxide (NO2), nitrogen oxides (NO(subscript x)) and ozone (O3) was conducted in Tianjin from September 8 to October 15, 2006. The data were used to investigate the relationship between the O3 distribution and its association with ambient concentrations of NO, NO2 and NO(subscript x) (NO and NO2). The measured concentrations of the pollutants in the study area varied as a function of time, while peaks in NO, NO2 and O3 all occurred in succession in the daytime. The diurnal cycle of ground-level ozone concentration showed a mid-day peak and lower nighttime concentrations. Furthermore, an inverse relationship was found between O3 NO, NO2 and NO(subscript x). In addition, a linear relationship between NO2 and NO(subscript x), as well as NO and NO(subscript x), and a polynomial relationship between O3 and NO2/NO was found. The variation in the level of oxidant (O3 and NO2) with NO2 was also obtained. It can be seen that OX concentration at a given location is made up of two parts: one independent and the other dependent on NO2 concentration. The independent part can be considered as a regional contribution and is about 20 ppb in Tianjin. An obvious difference in NO, NO(subscript x) and O3 concentrations between weekdays and weekends was also found, but this difference did not appear in NO2. Lastly, the diurnal variation of O3 concentration under different meteorological conditions was demonstrated and analyzed.

/pdf/analysis-of-the-relationship-between-o3-no-and-no2-in-4oexh3tgve.pdf

Analysis of the Relationship between O3, NO and NO2 in Tianjin, China

Impact of nocturnal planetary boundary layer on urban air pollutants: measurements from a 250-m tower over Tianjin, China.

A severe dust storm (SDS) event occurred during March-20 to March-22, 2010 in China. A regional dynamical model coupled with a dust model (WRF-Dust) is used for analyzing this SDS event. The distribution of API (air pollution index) values in China and satellite (moderate-resolution imaging spectroradiometer—MODIS) AOD (aerosol optical depth) data are used to trace the dust storm and to compare with the model result. Several model sensitive studies are performed to analyze the roles of physical processes (such as dust source, transport, and deposition) in controlling the SDS event. The result suggests that the Gobi Desert is a major dust source of the SDS event. By contrast, the Taklamakan Desert plays minor roles for affecting the high dust concentrations in eastern/southern China during the SDS event. This study also suggests that a large amount of dust particles was deposited at the surface during the transport pathway between the Gobi Desert and eastern/southern China, and the high surface concentrations of dust particles can be considered as a new dust source region, which produced dust air pollution when surface winds were strong. In this study, we define this process as a propagate dust source (PDS). The calculation shows that the calculated dust concentrations were considerably lower than the measured values in the downwind regions of deserts when the PDS process was not included in the model. By including the PDS process, the calculated dust pollution in eastern and southern China is considerably improved. The further detailed analysis shows that the PDS played important roles in controlling the long-range transport of dust particles during the SDS event. This study suggests that this regional dust model (WRF-Dust) is a useful tool to analyze the important processes of dust storms that are often occurred in China.

/pdf/analysis-of-a-severe-dust-storm-event-over-china-application-46m68vh4xl.pdf

Analysis of a severe dust storm event over China: Application of the WRF-Dust Model

Meteorological and aerosol data were measured at the atmospheric boundary layer observation station in Tianjin, China, and were analyzed to study the effects of aerosol mass, composition, and size distributions on visibility and short-wave radiation flux. The results show that fine particles played important roles in controlling visibility in Tianjin. The major contributors to light extinction coefficients included sulfate (28.7%), particulate organic matter (27.6%), elemental carbon (19.2%), and nitrate (6.1%). In addition to the measurement of aerosol composition, the size distribution of aerosol number concentrations were also measured and classified between haze days and non-haze days during spring. The extinction characteristics of ambient aerosol in haze days and non-haze days were calculated using Mie theory model. The average extinction coefficient and scattering coefficient of atmospheric aerosols were 0.253 1/km and 0.213 1/km in non-haze days, while 0.767 1/km and 0.665 1/km in haze days. A radiation transmission model LOWTRAN7 is also applied in this study. The model calculated radiant flux densities in haze days and non-haze days, which showed a fairly agreement with the observation results, showing that the heavy aerosol loadings in Tianjin had significantly impact on atmospheric visibility and radiation fluxes.

https://aaqr.org/articles/aaqr-11-05-oa-0073.pdf

Suqin Han

Papers

Analysis of the Relationship between O3, NO and NO2 in Tianjin, China

Impact of nocturnal planetary boundary layer on urban air pollutants: measurements from a 250-m tower over Tianjin, China.

Analysis of a severe dust storm event over China: Application of the WRF-Dust Model

Effect of Aerosols on Visibility and Radiation in Spring 2009 in Tianjin, China

Atmospheric metallic and arsenic pollution at an offshore drilling platform in the Bo Sea: A health risk assessment for the workers.