Impacts of aerosol-radiation feedback on local air quality during a severe haze episode in Nanjing megacity, eastern China

Abstract

Severe haze events and their radiation feedbacks exert a profound impact on the weather and tropospheric chemistry. Using the on-line-coupled Weather Research and Forecasting with Chemistry (WRF-Chem) model, this study investigates the impacts of direct aerosol-radiation feedbacks on local air quality (i.e. particulate matter and ozone photochemistry) during a severe autumn haze episode in Nanjing megacity, eastern China. Pronounced radiation feedbacks are found for the predictions of meteorological and chemical variables. In response to the negative radiative forcing of scattering-dominant anthropogenic haze aerosols, the instantaneous irradiance and temperature at the surface lower by 130 W m −2 and 1.1-1.4 °C, respectively, leading to a reduction of boundary layer height by 103.2-232.6 m (11-38%) and vertical wind speed by 0.1-0.8 mm s −1 (2-30% at mid-day) during this haze event. Such a stable atmosphere favours the accumulation of fine particles (30.5 μg m −3 , 28.7%) and NO 2 (6.0 ppb, 23.7%) in the urban pollution plume. The weaker turbulent mixing and photochemical activity associated with the enhanced titration loss, and reduced downward radiation and photolysis rate result in a 0.1−5.0 ppb (12.0%) reduction of near-surface ozone. The simulations highlight that the aerosol-radiation feedbacks play an important role in the atmospheric transport and chemistry of large urban pollution plumes.

Modeling of the Effects of Wintertime Aerosols on Boundary Layer Properties Over the Indo Gangetic Plain

“…Similar observations of enhancement in aerosol/trace gas concentration by aerosol‐boundary layer interaction were reported by number of studies, especially over East Asia (Ding et al, ; Li et al, ; Quan et al, ; Wang et al, ). Li et al () observed that the surface temperature decreases by 1.1 to 1.4 °C in regions of high aerosol loading (Nanjing City in China), which favored the accumulation of particles (30.5 μg/m 3 ) and gases (NO 2 , 6.0 ppb). Similarly, an increase of average surface PM 2.5 by 140 μg/m 3 over Beijing was reported by Wang et al ().…”

Amplified ozone pollution in cities during the COVID-19 lockdown

“…Furthermore, a reduction in PM 2.5 and PM 10 could also lead to an increase in surface O 3 concentrations (Liu et al, 2013;Li et al, 2017). As PM emissions were lower during the lockdown, the higher solar radiation favored O 3 formation (Heuss et al, 2003;Murphy et al, 2007;Wolff et al, 2013).…”

“…In addition to photochemical reactions, the heterogeneous chemical processes occurring on the surface of PM 2.5 and aerosols in the atmosphere are also an important way for the interaction between O 3 and PM 2.5 (Meng et al, 1997;Jacob, 2000;Deng et al, 2010;Li et al, 2011). In Nanjing, high concentrations of PM 2.5 (rising from 100 to 250 μg.m −3 ) resulted in a reduction of 130 W.m −2 of the irradiance and a 12% reduction of near-surface O 3 (Li et al, 2017).…”

Assessing the formation and evolution mechanisms of severe haze pollution in Beijing−Tianjin−Hebei region by using process analysis

“…It is well known that aerosols can scatter and absorb solar radiation to alter the radiative balance of the atmosphere and surface (direct radiative effect), and can serve as cloud condensation nuclei or ice nuclei to affect cloud properties (indirect radiative effect) (Twomey, 1974). These impacts are coupled with atmospheric dynamics to produce a chain of interactions with a large range of meteorological variables that influence both weather and climate (Ramanathan et al, 2001;Huang et al, 2006;Wu et al, 2009;Li et al, 2017d), which will further induce feedbacks on aerosol production, accumulation, and even severe haze pollutions (Petaja et al, 2016;Li et al, 2017b;Li et al, 2017e;Zhao et al, 2017;Gao et al, 2018). Based on multi-year measurements (from 2010 to 2016), Huang et al (2018) found that aerosol radiative effects led to a significant heating in the upper planetary boundary layer (PBL) and a substantial dimming at the surface over North China.…”