Ying Li

Enhancements of Major Aerosol Components Due to Additional HONO Sources in the North China Plain and Implications for Visibility and Haze

The Weather Research and Forecasting/Chemistry model (WRF-Chem) was updated by including photoexcited nitrogen dioxide (NO2) molecules, heterogeneous reactions on aerosol surfaces, and direct emissions of nitrous acid (HONO) in the Carbon-Bond Mechanism Z (CBM-Z). Five simulations were conducted to assess the effects of each new component and the three additional HONO sources on concentrations of major chemical components. We calculated percentage changes of major aerosol components and concentration ratios of gas NOy (NOyg) to NOy and particulate nitrates (NO3−) to NOy due to the three additional HONO sources in the North China Plain in August of 2007. Our results indicate that when the three additional HONO sources are included, WRF-Chem can reasonably reproduce the HONO observations. Heterogeneous reactions on aerosol surfaces are a key contributor to concentrations of HONO, nitrates (NO3−), ammonium (NH4+), and PM2.5 (concentration of particulate matter of ⩽2.5 μm in the ambient air) across the North China Plain. The three additional HONO sources produced a ∼5%–20% increase in monthly mean daytime concentration ratios of NO3− /NOy, a ∼15%–52% increase in maximum hourly mean concentration ratios of NO3−/NOy, and a ∼10%–50% increase in monthly mean concentrations of NO3− and NH4t+ across large areas of the North China Plain. For the Bohai Bay, the largest hourly increases of NO3− exceeded 90%, of NH4t+ exceeded 80%, and of PM2.5 exceeded 40%, due to the three additional HONO sources. This implies that the three additional HONO sources can aggravate regional air pollution, further impair visibility, and enhance the incidence of haze in some industrialized regions with high emissions of NOx and particulate matter under favorable meteorological conditions.

Impacts of Photoexcited NO2 Chemistry and Heterogeneous Reactions on Concentrations of O3 and NOy in Beijing,Tianjin and Hebei Province of China

Nitrous acid (HONO) plays a significant role in the photochemistry of the troposphere, especially in the polluted urban atmosphere, due to its photolysis by solar UV radiation into the hydroxyl radical (OH), which is one of the most important oxidant in the atmosphere (Alicke et al., 2002). Some previous observations showed unexpected high HONO concentrations up to several ppb at urban or rural sites during the daytime or nighttime (Qin et al., 2009; Su et al., 2008a, 2008b; Yu et al., 2009) but gas-phase chemical models usually underestimated HONO observations, particularly in the daytime. HONO sources are thought to be direct emissions, homogeneous gas reactions, and heterogeneous reactions on aerosol surfaces. Sarwar et al. (2008) incorporated gas-phase reactions, direct emissions, a heterogeneous reaction, and a surface photolysis reaction into the CMAQ model, and simulations still indicated HONO underestimation by comparison with measurements, especially in the daytime. Li et al. (2008) suggested a reaction of electronically excited nitrogen dioxide (NO2*) with water vapor as follows,

Effects of NOx and VOCs from Five Emission Sources on Summer Surface O3 over the Beijing-Tianjin-Hebei Region

The impacts of emissions from industry, power plant, transportation, residential, and biogenic sources on daily maximum surface ozone (O3DM) over the Beijing-Tianjin-Hebei (BTH) region in North China in the summer of 2007 were examined in a modeling study. The modeling system consisted of the Weather Research and Forecasting (WRF) model and the photochemical dispersion model, CAMx. The factor separation technique (FST) was used to quantify the effect of individual emission source types and the synergistic interactions among two or more types. Additionally, the effectiveness of emission reduction scenarios was explored. The industry, power plant, and transportation emission source types were found to be the most important in terms of their individual effects on O3DM. The key contributor to high surface O3 was power plant emissions, with a peak individual effect of 40 ppbv in the southwestern BTH area. The individual effect from the biogenic emission category was quite low. The synergistic effects from the combinations of each pair of anthropogenic emission types suppressed O3 formation, while the synergistic effects for combinations of three were favorable for O3 formation when the industrial and power plant emission source types coexisted. The quadruple synergistic effects were positive only with the combination of power plant, transportation, residential, and biogenic sources, while the quintuple synergistic effect showed only minor impacts on O3DM concentrations. A 30% reduction in industrial and transportation sources produced the most effective impacts on O3 concentrations, with a maximum decrease of 20 ppbv. These results suggested that the synergistic impacts among emission source types should be considered when formulating emission control strategies for O3 reduction.

Impacts of uncertainty in AVOC emissions on the summer ROx budget and ozone production rate in the three most rapidly-developing economic growth regions of China

High levels of uncertainty in non-methane volatile organic compound (NMVOC) emissions in China could lead to significant variation in the budget of the sum of hydroxyl (OH) and peroxy (HO2, RO2) radicals (ROx = OH + HO2 + RO2) and the ozone production rate [P(O3)], but few studies have investigated this possibility, particularly with three-dimensional air quality models. We added diagnostic variables into the WRF-Chem model to assess the impact of the uncertainty in anthropogenic NMVOC (AVOC) emissions on the ROx budget and P(O3) in the Beijing-Tianjin-Hebei region, Yangtze River Delta, and Pearl River Delta of China. The WRF-Chem simulations were compared with satellite and ground observations, and previous observation-based model studies. Results indicated that 68% increases (decreases) in AVOC emissions produced 4%–280% increases (2%–80% decreases) in the concentrations of OH, HO2, and RO2 in the three regions, and resulted in 35%–48% enhancements (26%–39% reductions) in the primary ROx production and ∼ 65% decreases (68%–73% increases) of the P(O3) in Beijing, Shanghai, and Guangzhou. For the three cities, the two largest contributors to the ROx production rate were the reaction of O1D + H2O and photolysis of HCHO, ALD2, and others; the reaction of OH + NO2 (71%–85%) was the major ROx sink; and the major contributor to P(O3) was the reaction of HO2 + NO (∼ 65%). Our results showed that AVOC emissions in 2006 from Zhang et al. (2009) have been underestimated by ∼ 68% in suburban areas and by 〉 68% in urban areas, implying that daily and hourly concentrations of secondary organic aerosols and inorganic aerosols could be substantially underestimated, and cloud condensation nuclei could be underestimated, whereas local and regional radiation was overestimated.

Effects of Additional HONO Sources on Visibility over the North China Plain

The objective of the present study was to better understand the impacts of the additional sources of nitrous acid (HONO) on visibility, which is an aspect not considered in current air quality models. Simulations of HONO contributions to visibility over the North China Plain (NCP) during August 2007 using the fully coupled Weather Research and Forecasting/Chemistry (WRF/Chem) model were performed, including three additional HONO sources: (1) the reaction of photo-excited nitrogen dioxide (NO*2) with water vapor; (2) the NO2 heterogeneous reaction on aerosol surfaces; and (3) HONO emissions. The model generally reproduced the spatial patterns and diurnal variations of visibility over the NCP well. When the additional HONO sources were included in the simulations, the visibility was occasionally decreased by 20%–30% (3–4 km) in local urban areas of the NCP. Monthly-mean concentrations of NO3−, NH4+, SO42− and PM2.5 were increased by 20%–52% (3–11 μg m−3), 10%–38%, 6%–10%, and 6%–11% (9–17 μg m−3), respectively; and in urban areas, monthly-mean accumulationmode number concentrations (AMNC) and surface concentrations of aerosols were enhanced by 15%–20% and 10%–20%, respectively. Overall, the results suggest that increases in concentrations of PM2.5, its hydrophilic components, and AMNC, are key factors for visibility degradation. A proposed conceptual model for the impacts of additional HONO sources on visibility also suggests that visibility estimation should consider the heterogeneous reaction on aerosol surfaces and the enhanced atmospheric oxidation capacity due to additional HONO sources, especially in areas with high mass concentrations of NOx and aerosols.

Impacts of additional HONO sources on O3 and PM2.5 chemical coupling and control strategies in the Beijing-Tianjin-Hebei region of China

The objective of this work is to examine the impacts of additional HONO sources on the chemical interaction between ozone (O3) and particulate matter with a diameter≤2.5 µm (PM2.5). Three additional HONO sources, i.e. HONO emissions, the reaction of photo-excited nitrogen dioxide (NO2 *) with water vapour (H2O), and NO2 heterogeneous reaction on aerosol surfaces, were inserted into the fully coupled Weather Research and Forecasting-Chemistry model to evaluate O3 and PM2.5 concentration enhancements in the Beijing–Tianjin–Hebei (BTH) region during August 2007. Results show that the additional HONO sources significantly increase O3 and PM2.5 concentrations during daytime. Up to 9 ppb enhancements of O3 and 32 µg m−3 increases in PM2.5 are found at seven urban sites over the BTH region. O3 increases are closely connected to PM2.5 increases over urban areas during daytime when the additional HONO sources are taken into account. PM2.5 inorganic components of , and are increased by 5–18, 10–58 and 10–40%, respectively, over urban areas during daytime. The simultaneous increment of O3 and PM2.5 during daytime due to the additional HONO sources is related to the increasing oxidants (OH, H2O2 and O3) that enhance the atmospheric oxidising capacity. The concentration variations of O3 and PM2.5 under a variety of NOx, volatile organic compound and ammonia (NH3) emission control scenarios show that the additional HONO sources increase the sensitivity of O3 and PM2.5 concentrations to the changes of NOx emissions. An increase of the PM2.5 sensitivity to changes in NH3 emissions is also found. This indicates that without considering the additional HONO sources, the effectiveness of emission control strategies in reducing O3 and PM2.5 concentrations would be significantly underestimated.