Impacts of aerosol direct effects on tropospheric ozone through changes in atmospheric dynamics and photolysis rates

Abstract

<p><strong>Abstract.</strong> Aerosol direct effects (ADE), i.e., scattering and absorption of incoming solar radiation, reduce radiation reaching the ground and the resultant photolysis attenuation can decrease ozone (O<sub>3</sub>) formation in polluted areas. One the other hand, evidence also suggests that ADE associated cooling suppresses atmospheric ventilation thereby enhancing surface-level O<sub>3</sub>. Assessment of ADE impacts is thus important for understanding emission reduction strategies that seek co-benefits associated with reductions in both particulate matter and O<sub>3</sub> levels. This study quantifies the impacts of ADE on tropospheric ozone by using a two-way online coupled meteorology and atmospheric chemistry model, WRF-CMAQ, instrumented with process analysis methodology. Two manifestations of ADE impacts on O<sub>3</sub> including changes in atmospheric dynamics (ΔDynamics) and changes in photolysis rates (ΔPhotolysis) were assessed separately through multiple scenario simulations for January and July of 2013 over China. Results suggest that ADE reduced surface daily maxima 1 h O<sub>3</sub> (DM1O<sub>3</sub>) in China by up to 39 μg m<sup>-3</sup> through the combination of ΔDynamics and ΔPhotolysis in January, but enhanced surface DM1O<sub>3</sub> by up to 4 μg m<sup>-3</sup> in July. Increased O<sub>3</sub> in July is largely attributed to ΔDynamics which causes a weaker O<sub>3</sub> sink of dry deposition and a stronger O<sub>3</sub> source of photochemistry due to the stabilization of atmosphere. Meanwhile, surface OH is also enhanced at noon in July, though its daytime average values are reduced in January. An increased OH chain length and a shift towards more VOC-limited condition are found due to ADE in both January and July. This study suggests that reducing ADE may have potential risk of increasing O<sub>3</sub> in winter, but it will benefit the reduction of maxima O<sub>3</sub> in summer.</p>

The Impact of the Direct Effect of Aerosols on Meteorology and Air Quality Using Aerosol Optical Depth Assimilation During the KORUS‐AQ Campaign

“…The cloud fraction in the lowest layer also increased over the ocean. As the lower PBLH over land prevented the ventilation of pollutants over the surface, air pollution became worse, especially near sources of emissions (Wang et al, ; Xing et al, ).…”

“…To achieve a more thorough understanding of meteorology, air quality, and their interaction, we must identify the effects of aerosols on the radiative budget (Wong et al, ). A number of studies have used satellite data and numerical models to quantify both the direct and indirect effects of aerosols and meteorological (climatological) responses (Haywood & Boucher, ; Jacob & Winner, ; Takemura et al, ; Wang et al, ; Wong et al, ; Xing et al, ; Xing et al, ; Xing et al, ; Yu et al, ). Xing et al () found that the direct effect of aerosols increases the concentration of surface air pollutants as a result of the stabilization of the atmosphere, which reduces ventilation.…”

“…Wang et al () showed that reduced surface solar radiation of up to 53% in Beijing reduced the PBLH from 690 to 590 m, which in turn it increased PM 2.5 concentrations during the haze period in 2013. In addition, because of changes in atmospheric dynamics and photochemical reactions by direct aerosol effects, the O 3 formation over a surface can be profoundly affected (Wong et al, ; Xing et al, ).…”

Increased Global Land Carbon Sink Due to Aerosol‐Induced Cooling

“…Additionally, aerosols decrease soil pH through N and sulfur (S) deposition, which may accelerate leaching and reduce the availability of nutrients to plants, leading to C loss (Bowman et al, ). Furthermore, sulfate aerosols can oxidize photosynthesis tissues (Eliseev, ), and other aerosols affect the photochemical processes producing near‐surface ozone (Xing et al, ), which impairs stomatal conductance and photosynthesis (Sitch et al, ).…”

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

“…One of the major factors influencing the change in ozone concentration in a polluted hazy atmosphere, as mentioned in the earlier studies, is the reduction in solar radiation within the lower boundary layer due to aerosol forcing and feedbacks (Jiang et al, ; Li et al, ; Wong et al, ). Some studies also provide evidence of increase in surface level O 3 with aerosol feedback linked to suppressed atmospheric ventilation (Chen et al, ; Xing et al, ) rather than photochemistry. The observed increase in O 3 in the present study (at Kharagpur) may be associated with reduced ventilation (due to the decrease in boundary layer height and wind speed), which enhanced the precursor levels (CO and NO x in Figure ) and thus increased photochemistry resulting in greater O 3 chemical formation.…”