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Naphthalene (Nap) and its derivatives, including 1-methylnaphthalene (1-MN) and 2-methylnaphthalene (2-MN), serve as prominent intermediate volatile organic compounds (IVOCs) contributing to the formation of secondary organic carbon (SOC). In this study, the Community Multi-Scale Air Quality (CMAQ) model coupled with detailed emissions and reactions of these compounds was utilized to examine their roles in the formation of SOC and other secondary pollutants in the Yangtze River Delta (YRD) region during summer. Remarkably, significant underestimations of Nap and MN concentrations (by 79% and 85%) were observed at the Taizhou site. To better capture the temporal variations of Nap and MN, their emissions in the YRD region were scaled up by a factor of 5 and 7, respectively, with constraints based on field measurements. After adjusting their emissions, Nap concentrations reached 27 ppt in the YRD, accounting for 4.1% and 9.1% (up to 13.7%) of total aromatics emissions and aromatic-derived SOC, respectively. 1- MN and 2-MN were relatively low, with an average of 3 and 6 ppt in the YRD, and contributed 3.1% of aromatic-derived SOC. The influences of Nap and MN oxidation on ozone and radicals might be trivial on a regional scale but were not negligible when considering daily fluctuations, particularly in Shanghai and Suzhou. This study emphasizes the high SOC formation potentials of Nap and MN, which may pose environmental risks and adverse health. [ABSTRACT FROM AUTHOR]

Volatile organic compounds (VOCs) play a crucial role in the formation of tropospheric ozone (O3) and secondary organic aerosols. VOC emissions are generally considered to have larger uncertainties compared to other pollutants, such as sulphur dioxide and fine particulate matter (PM2.5). Although predictions of O3 and PM2.5 have been extensively evaluated in air quality modelling studies, there has been limited reporting on the evaluation of VOCs, mainly due to a lack of routine VOCs measurements at multiple sites. In this study, we utilized VOCs measurements from the ATMSYC project at 28 sites across China and assessed the predicted VOCs concentrations using the Community Multiscale Air Quality (CMAQ) model with the widely used Multi-resolution Emission Inventory for China (MEIC). The ratio of predicted to observed total VOCs was found to be 0.74 ± 0.40, with underpredictions ranging from 2.05 to 50.61 ppbv (5.77% to 85.40%) at 24 sites. A greater bias in VOCs predictions was observed in industrial cities in the north and southwest, such as Jinan, Shijiazhuang, Lanzhou, Chengdu, and Guiyang. In terms of different VOC components, alkanes, alkenes, non-naphthalene aromatics (ARO2MN), and alkynes were consistently underpredicted, with ratios of predicted to observed of 0.53 ± 0.38, 0.51 ± 0.48, 0.31 ± 0.38, and 0.41 ± 0.47, respectively. Sensitivity experiments were conducted to assess the impact of the VOCs prediction bias on O3 predictions. While emission adjustments improved the model performance for VOCs, resulting in a ratio of total VOCs to 0.86 ± 0.47, they also exacerbated O3 overprediction relative to the base case by 0.62% to 6.27% across the sites. This study demonstrates that current modelling setups and emission inventories are likely to underpredict VOCs concentrations, and this underprediction of VOCs contributes to lower O3 predictions in China. [ABSTRACT FROM AUTHOR]

Ozone (O3) has become a significant air pollutant in China in recent years. O3 abatement is challenging due to the nonlinear response of O3 to precursors nitrogen oxides (NOx) and volatile organic compounds (VOCs). Photochemical indicators are widely used to estimate the O3-NOx-VOC sensitivity, and this has important policy implications. However, the effectiveness of the indicators has seldom been evaluated. This study examines the applications of four indicators that include the ratio of the production rates of H2O2 and HNO3 (PH2O2/PHNO3), HCHO/NO2, HCHO/NOy, and reactive nitrogen (NOy) in the Yangtze River Delta (YRD) with localized thresholds. The overall accuracy was high (> 92%) for all indicators and not significantly reduced with different simulation periods or in different locations of the region. By comparing with the O3 isopleths, it was found that HCHO/NO2 and HCHO/NOy showed the most consistency, whereas PH2O2/PHNO3 (NOy) tended to underestimate (overestimate) the positive response of O3 to NOx. Additionally, PH2O2/PHNO3 was less likely to attribute the O3 formation to mixed sensitivity than the other indicators, and this demonstrated a preference for a single-pollutant control strategy. This study also revealed that the details in the methodology used to derive the threshold values impacted the results, and this may produce uncertainties in the application of photochemical indicators. [ABSTRACT FROM AUTHOR]

Naphthalene (Nap) and its derivatives, including 1-methylnaphthalene (1-MN) and 2-methylnaphthalene (2-MN), serve as prominent intermediate volatile organic compounds (IVOCs) and contribute to the formation of secondary organic aerosol (SOA). In this study, the Community Multiscale Air Quality (CMAQ) model coupled with detailed emissions and reactions of these compounds was utilized to examine their roles in the formation of SOA and other secondary pollutants in the Yangtze River Delta (YRD) region during summer. Significant underestimations of Nap and MN concentrations (by 79 % and 85 %) were observed at the Taizhou site based on the model results using the default emissions. Constrained by the observations, anthropogenic emissions of Nap and MN in the entire region were multiplied by 5 and 7, respectively, to better capture the evolution of pollutants. The average concentration of Nap reached 25 ppt (parts per trillion) in the YRD, with Nap contributing 4.1 % and 8.1 % (up to 12.6 %) of total aromatic emissions and aromatic-derived secondary organic carbon (SOC), respectively. The concentrations of 1-MN and 2-MN were relatively low, averaging 2 and 5 ppt, respectively. Together, they accounted for only 2.4 % of the aromatic-derived SOC. The impacts of Nap and MN oxidation on ozone and radicals were insignificant at regional scales but were not negligible when considering daily fluctuations in locations with high emissions of Nap and MN. This study highlights the significant roles of Nap and MN in the formation of SOA, which may pose environmental risks and result in adverse health effects. [ABSTRACT FROM AUTHOR]

Volatile organic compounds (VOCs) play a crucial role in the formation of tropospheric ozone (O 3) and secondary organic aerosols. VOC emissions are generally considered to have larger uncertainties compared to other pollutants, such as sulfur dioxide and fine particulate matter (PM 2.5). Although predictions of O 3 and PM 2.5 have been extensively evaluated in air quality modeling studies, there has been limited reporting on the evaluation of VOCs, mainly due to a lack of routine VOC measurements at multiple sites. In this study, we utilized VOC measurements from the "Towards an Air Toxic Management System in China" (ATMSYC) project at 28 sites across China and assessed the predicted VOC concentrations using the Community Multiscale Air Quality (CMAQ) model with the widely used Multi-resolution Emission Inventory for China (MEIC). The ratio of predicted to observed total VOCs was found to be 0.74 ± 0.40, with underpredictions ranging from 2.05 to 50.61 ppbv (5.77 % to 85.40 %) at 24 sites. A greater bias in VOC predictions was observed in industrial cities in the north and southwest, such as Jinan, Shijiazhuang, Lanzhou, Chengdu, and Guiyang. In terms of different VOC components, alkanes, alkenes, non-naphthalene aromatics (ARO2MN), alkynes, and formaldehyde (HCHO) had prediction-to-observation ratios of 0.53 ± 0.38, 0.51 ± 0.48, 0.31 ± 0.38, 0.41 ± 0.47, and 1.21 ± 1.61, respectively. Sensitivity experiments were conducted to assess the impact of the VOC prediction bias on O 3 predictions. While emission adjustments improved the model performance for VOCs, resulting in a change in the ratio of total VOCs to 0.86 ± 0.47, they also exacerbated O 3 overprediction relative to the base case by 0.62 % to 6.27 % across the sites. This study demonstrates that current modeling setups and emission inventories are likely to underpredict VOC concentrations, and this underprediction of VOCs contributes to lower O 3 predictions in China. [ABSTRACT FROM AUTHOR]

In 2021, the World Health Organization ranked Nigeria among the most polluted nations in the world, an indication of a deteriorating air quality, especially in the major urban areas of the country, which might pose adverse human health impacts. In this study, the Integrated Source Apportionment Method (ISAM) tool in the Community Multiscale Air Quality (CMAQ) model (CMAQ‐ISAM) was employed to quantify the contributions of eight emissions sectors to fine particulate matter (PM2.5) and its major components in Lagos during a prolonged severe atmospheric pollution episode (APE) in January 2021. The influence of meteorological conditions on the formation and dispersion of PM2.5 during the APE was also elucidated. Spatially, elevated PM2.5 concentrations were found in the northwestern region of Lagos, an urban area with larger anthropogenic emissions. Residential and industry were the two major sources of PM2.5. Residential contributed the most to total PM2.5 (∼40 μg/m3), followed by industry (∼20 μg/m3). High concentrations of secondary inorganic aerosols (SIA) at the northwest and upper northern areas of Lagos were majorly attributed to residential and industry sectors. In addition, sulfate accounted for the largest fraction of PM2.5, with residential, industry, and energy being its major sources. Residential, industry, and on‐road sectors dominated the contributions to nitrate, while residential and industry were the major contributors to ammonium. Furthermore, the elevated PM2.5 concentrations during the APE were greatly enhanced by unfavorable meteorological conditions. This study provides insights for designing effective emissions control strategies to mitigate future severe PM2.5 pollution episode in Lagos. Plain Language Summary: With a population of about 23.5 million as at 2018, Lagos is the largest metropolitan city in Africa, and also the most economically and industrially‐developed city in Nigeria. As a result, the city has been suffering from severe fine particulate matter (PM2.5) pollution for more than two decades. In January 2021, a prolonged severe atmospheric pollution episode (APE) occurred in the city. In this study, the contributions of eight emissions sectors to PM2.5 and its major components, as well as the meteorological influences on PM2.5 pollution during the APE were elucidated. The results provide insights into the emissions sectors dominating PM2.5 pollution in Lagos as well as the meteorological influences, and could be used to better understand the causal factors of PM2.5 pollution episode in other areas of the world that can then be applied to develop more effective control strategies that would reduce the magnitude of the episode and better protect public health. Key Points: Lagos experienced a prolonged severe PM2.5 pollution episode in January 2021PM2.5 pollution was enhanced by unfavorable meteorological conditionsEffective emissions control strategies to reduce PM2.5 concentrations are urgently required in Lagos [ABSTRACT FROM AUTHOR]

Ozone (O 3) has become a significant air pollutant in China in recent years. O 3 abatement is challenging due to the nonlinear response of O 3 to precursors nitrogen oxides (NO x) and volatile organic compounds (VOCs). Photochemical indicators are widely used to estimate the O 3 –NO x –VOC sensitivity, and this has important policy implications. However, the effectiveness of the indicators has seldom been evaluated. This study examined the applications of four indicators that include the ratio of the production rates of H 2 O 2 and HNO 3 (PH2O2/PHNO3), HCHO/NO2 , HCHO/NOy , and reactive nitrogen (NO y) in the Yangtze River Delta (YRD) with localized thresholds. The overall accuracy was high (>92%) for all indicators and not significantly reduced with different simulation periods or in different locations of the region. By comparing with the O 3 isopleths, it was found that HCHO/NO2 and HCHO/NOy showed the most consistency, whereas PH2O2/PHNO3 (NO y) tended to underestimate (overestimate) the positive response of O 3 to NO x. Additionally, PH2O2/PHNO3 was less likely to attribute the O 3 formation to mixed sensitivity than the other indicators, and this demonstrated a preference for a single-pollutant control strategy. This study also revealed that the details in the methodology used to derive the threshold values impacted the results, and this may produce uncertainties in the application of photochemical indicators. [ABSTRACT FROM AUTHOR]