Haze Events Research Articles

Impact of Haze Event on Daily Admission of Respiratory System Patients in Peninsular Malaysia

Diseases of the respiratory system, especially in children and the elderly, are significantly related to air pollution. Exposure to air pollution has led to an increase in the number of patients who need hospital treatment. The purpose of this study was to learn about the effects of changes in the levels of major pollutant components on the number of daily hospital admissions of respiratory system patients. The generalised linear lag model is used in this study to demonstrate the lag structure of the exposure-response impacts. The results show that particulate matter (PM10), nitrogen dioxide (NO2), carbon monoxide (CO), and ozone (O3) component factors, as well as meteorological factors like wind speed and ultraviolet (UV) radiation, affect the number of hospital admissions of respiratory system patients. The best model is a lag 6 negative binomial regression model. Daily hospital admission is positively correlated with PM10, NO2, and wind speed, and negatively correlated with CO, O3, and UV radiation. According to the findings of the study, fine particulate matter (PM2.5) and sulphur dioxide (SO2), as well as temperature, humidity, and wind direction, are not significantly contributing factors in the number of respiratory system patients admitted to hospitals.

Sources and composition of elemental carbon during haze events in North China by a high time-resolved study

Despite the implementation of stringent emission reduction measures in the past year, severe winter haze events still occurred frequently in North China, with only marginal decreases observed in elemental carbon (EC) concentrations. EC not only constitutes a fraction of particle mass but also interacts with boundary layer and influences haze formation. Given the complex composition of EC, characterizing its sources and composition during haze processes is challenging yet crucial for understanding haze formation and evolution. Here, hourly-resolution PM2.5 samples were collected during three different haze event (P1-P3) in the North China Plain to investigate dynamic changes in EC source across different haze processes. The average EC concentrations and char/soot ratios were 9.94 ± 4.80 μgC·m−3, 14.5 ± 6.93 μgC·m−3, 15.9 ± 5.54 μgC·m−3, and 2.42 ± 0.98, 2.70 ± 0.88, 2.61 ± 0.95 for P1, P2 and P3, respectively. Backward trajectory analysis showed distinct variations in EC concentration and composition under the influence of different air masses during the three haze events, with local air masses influenced days exhibiting higher EC concentrations and char/soot ratios. The char/soot ratio based diagnostic method suggested that EC was predominantly influenced by coal combustion and vehicle emissions. Further positive matrix factorization analysis suggested that biomass burning and residential coal combustion were the main contributors of EC (58 %) and played a dominant role in driving variations in EC concentrations during haze episodes. Potential source contribution function analysis results highlight that local biomass burning and residential coal combustion could be major reason for the EC elevation in different haze events. Our results provide valuable insights into the sources and composition of EC during haze events, facilitating the implementation of effective measures for mitigating both EC and PM pollution.

Study of Haze Boundary Layer Features Based on Multi-Source Data in Shihezi, China

To reveal the temporal–spatial characteristics of air pollution during winter haze events on the north slope of the Tianshan mountains, a combined detection experiment was conducted in this study using a tethered airship, Lidar, and ground monitors from December 2019 to January 2020 in Shihezi. First, the boundary layer height (BLH) was calculated using the temperature, relative humidity, wind speed, and atmospheric pressure detected by the tethered airship; the BLHs were mainly distributed from 200 m to 450 m, with the visibility (V) mainly less than 3000 m. Subsequently, the temporal–spatial characteristics of the atmospheric pollutants were analyzed. The results show that during winter haze events, the temperature was mainly between −5 °C and −15 °C, and the relative humidity was between 60% and 75%, with a wind speed of less than 2 m/s. Moreover, the temperature difference (ΔT) within the BLH was basically greater than 0, except from 14:00 to 18:00, and a larger ΔT corresponded to a lower V and more severe pollution, which indicates that the sensible heat flux is very weak, and the atmospheric structure is very stable. Meanwhile, the PM2.5 and PM10 were mainly concentrated between 130 and 180 μg·m−3 and between 160 and 230 μg·m−3, respectively; the maximum PM2.5 and PM10 appeared at 11:00–13:00. Furthermore, the black carbon was distributed at 6–8 μg·m−3 and decreased significantly around the BLH. Moreover, the extinction coefficient (EC) had a negative correlation with the V, and the maximum of the EC was 9 km−1 when V was the minimum (less than 1500 m) from 10:00 to 11:00. Finally, the relationship between V and the air quality index (AQI) is constructed as AQI=456e−0.00061V. The conclusions obtained provide a reference for haze elimination and environmental governance of the locale.

Aqueous-Phase Reactions of Anthropogenic Emissions Lead to the High Chemodiversity of Atmospheric Nitrogen-Containing Compounds during the Haze Event.

Nitrogen-containing organic compounds (NOCs), a type of important reactive-nitrogen species, are abundant in organic aerosols in haze events observed in Northern China. However, due to the complex nature of NOCs, the sources, formation, and influencing factors are still ambiguous. Here, the molecular composition of organic matters (OMs) in hourly PM2.5 samples collected during a haze event in Northern China was characterized using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). We found that CHON compounds (formulas containing C, H, O, and N atoms) dominated the OM fractions during the haze and showed high chemodiversity and transformability. Relying on the newly developed revised-workflow and oxidation-hydrolyzation knowledge for CHON compounds, 64% of the major aromatic CHON compounds (>80%) could be derived from the oxidization or hydrolyzation processes. Results from FT-ICR MS data analysis further showed that the aerosol liquid water (ALW)-involved aqueous-phase reactions are important for the molecular distribution of aromatic-CHON compounds besides the coal combustion, and the ALW-involved aromatic-CHON compound formation during daytime and nighttime was different. Our results improve the understanding of molecular composition, sources, and potential formation of CHON compounds, which can help to advance the understanding for the formation, evolution, and control of haze.

Spatial and Temporal Variation of Particulate Matter (PM10 and PM2.5) and Its Health Effects during the Haze Event in Malaysia

This study aims to assess and compare levels of particulate matter (PM10 and PM2.5) in urban and industrial areas in Malaysia during haze episodes, which typically occur in the south west monsoon season. The high concentrations of atmospheric particles are mainly due to pollution from neighbouring countries. Daily PM concentrations were analysed for urban and industrial areas including Alor Setar, Tasek, Shah Alam, Klang, Bandaraya Melaka, Larkin, Balok Baru, and Kuala Terengganu in 2018 and 2019. The analysis employed spatiotemporal to examine how PM levels were distributed. The data summary revealed that PM levels in all study areas were right-skewed, indicating the occurrence of high particulate events. Significant peaks in PM concentrations during haze events were consistently observed between June and October, encompassing the south west monsoon and inter-monsoon periods. The study on acute respiratory illnesses primarily focused on Selangor. Analysis revealed that Klang had the highest mean number of inpatient cases for acute exacerbation of bronchial asthma (AEBA) and acute exacerbation of chronic obstructive pulmonary disease (AECOPD) with values of 260.500 and 185.170, respectively. Similarly, for outpatient cases of AEBA and AECOPD, Klang had the highest average values of 41.67 and 14.00, respectively. Shah Alam and Sungai Buloh did not show a significant increase in cases during periods of biomass burning. The statistical analysis concluded that higher concentrations of PM were associated with increased hospital admissions, particularly from June to September, as shown in the bar diagram. Haze episodes were associated with more healthcare utilization due to haze-related respiratory illnesses, seen in higher inpatient and outpatient visits (p < 0.05). However, seasonal variability had minimal impact on healthcare utilization. These findings offer a comprehensive assessment of PM levels during historic haze episodes, providing valuable insights for authorities to develop policies and guidelines for effective monitoring and mitigation of the negative impacts of haze events.

Evolution of atmospheric age of particles and its implications for the formation of a severe haze event in eastern China

Abstract. Atmospheric age reflects how long particles have been suspended in the atmosphere, which is closely associated with the evolution of air pollutants. Severe regional haze events occur frequently in China, influencing air quality, human health, and regional climate. Previous studies have explored the characteristics of mass concentrations and compositions of fine particulate matter (PM2.5) during haze events, but the evolution of atmospheric age remains unclear. In this study, the age-resolved University of California, Davis/California Institute of Technology (UCD/CIT) model was developed and applied to simulate the concentration and age distribution of PM2.5 during a severe regional haze episode in eastern China. The results indicated that PM2.5 concentrations in the North China Plain (NCP) gradually accumulated due to stagnant weather conditions during the beginning stage of the haze event. Accordingly, the atmospheric age of elemental carbon (EC), primary organic aerosol (POA), sulfate (SO42-), and secondary organic aerosol (SOA) gradually increased. The subsequent PM2.5 concentration growth was driven by the local chemical formation of nitrate (NO3-) under high relative humidity. The newly formed NO3- particles led to a decrease in the mean atmospheric age of NO3- particles. During the regional transport stage, aged particles from the NCP moved to the downwind Yangtze River Delta (YRD) region, leading to a sharp increase in PM2.5 concentrations and the average age of EC, POA, SO42-, and SOA in YRD. In contrast, the average age of NO3- and ammonium remained unchanged or even slightly decreased due to continuous local formation in the YRD region. Different evolution of the atmospheric age among these components provides a unique perspective on the formation of PM2.5 components during the regional haze event. The information can also be used for designing effective control strategies for different components of PM2.5.

Comparing sources of carbonaceous aerosols during haze and nonhaze periods in two northern Chinese cities

Radiocarbon (14C), stable carbon isotope (13C), and levoglucosan in PM2.5 were measured in two northern Chinese cities during haze events and nonhaze periods in January 2019, to ascertain the sources and their differences in carbonaceous aerosols between the two periods. The contribution of primary vehicle emissions (17.8 ± 3.7%) to total carbon in Beijing during that haze event was higher than that of primary coal combustion (7.3 ± 4.2%), and it increased significantly (7.1%) compared to the nonhaze period. The contribution of primary vehicle emissions (4.1 ± 2.8%) was close to that of primary coal combustion (4.3 ± 3.3%) during the haze event in Xi'an, and the contribution of primary vehicle emissions decreased by 5.8% compared to the nonhaze period. Primary biomass burning contributed 21.1 ± 10.5% during the haze event in Beijing and 40.9 ± 6.6% in Xi'an (with an increase of 3.3% compared with the nonhaze period). The contribution of secondary fossil fuel sources to total secondary organic carbon increased by 29.2% during the haze event in Beijing and by 18.4% in Xi'an compared to the nonhaze period. These results indicate that specific management measures for air pollution need to be strengthened in different Chinese cities in the future, that is, controlling vehicle emissions in Beijing and restricting the use of coal and biomass fuels in winter in Xi'an.

Double Inversion Layers Affect Fog–Haze Events over Eastern China—Based on Unmanned Aerial Vehicles Observation

The goal of this work is to analyze how double inversion layers affect fog–haze events and boundary layers over Eastern China based on unmanned aerial vehicle observations. During 10–12 December 2020, two successive fog–haze events occurred in Eastern China. Based on the unmanned aerial vehicle (UAV), wind, temperature, relative humidity (RH), and aerosol mass concentration were monitored simultaneously in Lianyungang, China. Several observations were found after analyzing the physical fields of these data. The results show that the concentrations of air pollutants during fog events were negatively correlated with horizontal visibilities. The mass concentrations of particulate matter increased rapidly (After 08:00 BJT 11) in the fog dissipation stages (PM2.5 and PM10 increased from 97 and 150 μg/m3 to 213 and 300 μg/m3, respectively). Double temperature inversion significantly affected fog events, where the enhancement of the lower-level temperature inversion (where the inversion layer top height was between 150 and 300 m) corresponded to the explosive growth of fog and the dissipation of the upper-level inversion layer. (The bottom height of the inversion layer was between 350 m and 600 m) This indicates the end of fog events. Fog layer thicknesses are negatively correlated with the concentrations of air pollutants in the near-surface layer. The thickening of the inversion layer near the surface corresponds to an increase (after 05:00 BJT 11 and 03:00 BJT 12) in fog layer height. The fog event is maintained when water vapor conditions are favorable enough or when there is a deep near-surface temperature inversion but the maintenance of the near-surface temperature inversion at an intensity of above 2 °C (100 m)−1 mainly contributes to the durations of these two fog events. Calculations through the trajectory model reveal that the air pollutant source varied during these two events, which was the main reason for the difference in air pollutant concentrations between the two events.

Aqueous‐Phase Secondary Processes and Meteorological Change Promote the Brown Carbon Formation and Transformation During Haze Events

AbstractThe evolution and the impacts of meteorological conditions on brown carbon (BrC) absorption are not understood, which hinders the assessment of BrC radiative forcing. To address this issue, 1‐hr time‐resolved PM2.5 samples collected during three haze events in the North China Plain prior to the COVID‐19 pandemic were used to measure the optical properties of BrC. By coupling excitation‐emission matrix spectroscopy, chemical tracer analysis with multiple model analysis including positive matrix factorization (PMF) and a deweather‐random forest model, we found that a higher proportion of highly oxidized chromophoric components was present in water‐soluble BrC than in methanol‐soluble BrC, indicating the conversion of low‐oxidized water‐insoluble BrC into highly oxidized water‐soluble BrC during the day. The results of the PMF and the deweather‐random forest model showed that aqueous secondary processes were the major contributor to the BrC absorption (68% ± 38%), and the changes in meteorological conditions such as relative humidity (RH) could significantly lead to the changes in the light‐absorbing capacity of BrC, especially the enhancement for water‐soluble BrC and bleaching for methanol‐soluble BrC during the noon and afternoon. We further found that the BrC absorption capacity increased as RH increases to a maximum of ∼65%, and then decreased when RH >65%, highlighting the important role of RH in the generation of water‐soluble BrC.

The impact of aerosol-meteorology feedback on the effectiveness of emission reduction for PM2.5: A modeling case study in Northern China

The quantification of the effectiveness of anthropogenic emission control measures is crucial for future air quality policies. Meteorology plays a vital role in haze pollution, and the interactions between aerosol and meteorology have been widely studied. However, it is not fully clear how aerosol-meteorology feedback affects the effectiveness of emission reduction for PM2.5, which limits our ability of optimizing anti-pollution policies. Here, with the two-way atmospheric chemical transport model WRF-Chem, the effects of aerosol-meteorology feedback on the effectiveness of emission reduction for PM2.5 during a winter severe haze event in 2016 over the Northern China Plain (NCP) are studied. In the more polluted area of NCP (MP_NCP) during the daytime, 20% emission reduction over NCP increases near-surface downward shortwave radiation by 4.62 W/m2, 2 m temperature by 0.08 °C, boundary layer height by 7.19 m and reduces 2 m relative humidity by 0.31% and thereby alleviates worsened meteorological conditions caused by aerosol effect. As a result, in MP_NCP, 20% emission reduction without aerosol-meteorology feedback leads to a decrease of 40.49μg/m3 of near-surface PM2.5 and the above meteorological changes decrease near-surface PM2.5 concentration by 7.82μg/m3, indicating that aerosol-meteorology feedback strengthens the effectiveness of emission reduction by 19%. In the less polluted area (LP_NCP), aerosol effect induced meteorological changes decrease PM2.5 concentration by 7.57μg/m3 and 20% emission reduction without aerosol-meteorology feedback leads to a decrease of 13.15μg/m3 in near-surface PM2.5. This reveals a remarkable enhancement of 58% in the effectiveness of emission reduction, which is much larger than that in MP_NCP. Such difference can be attributed to the presence of more clouds in LP_NCP, where the decrease in liquid water path, along with the increase in the planetary boundary layer height, jointly contributes to the PM2.5 decrease. Moreover, the effect of aerosol-meteorology feedback on the effectiveness of emission reduction for PM2.5 is nonlinear. With increasing PM2.5 concentration, the aerosol-meteorology feedback induced PM2.5 reduction first increases and then stabilizes once the PM2.5 concentration exceeds 350 μg m−3. This study can provide reference for air pollution control strategies.

Superimposed effects of typical local circulations driven by mountainous topography and aerosol–radiation interaction on heavy haze in the Beijing–Tianjin–Hebei central and southern plains in winter

Abstract. Although China's air quality has substantially improved in recent years due to the vigorous emissions reduction, the Beijing–Tianjin–Hebei (BTH) region, especially its central and southern plains at the eastern foot of the Taihang Mountains, has been the most polluted area in China, with persistent and severe haze in winter. Combining meteorology–chemistry coupled model simulations and multiple observations, this study explored the causes of several heavy haze events in this area in January 2017, focusing on local circulations related to mountain terrain. The study results showed that on the weather scale, the configuration of the upper, middle, and lower atmosphere provided favorable weather and water vapor transport conditions for the development of haze pollution. Under the weak weather-scale systems, local circulation played a dominant role in the regional distribution and extreme values of PM2.5. Influenced by the Taihang and Yanshan mountains, vertical circulations and wind convergence zone were formed between the plain and mountain slopes. The vertical distribution of pollutants strongly depended on the intensity and location of the circulation. The circulation with high intensity and low altitude was more unfavorable for the vertical and horizontal diffusion of near-surface pollutants. More importantly, we found that the aerosol–radiation interaction (ARI) significantly amplified the impacts of local vertical circulations on heavy haze by two mechanisms. First, the ARI strengthened the vertical circulations at the lower levels, with the zonal wind speeds increasing by 0.3–0.8 m s−1. Meanwhile, the ARI could cause a substantial downward shift in the vertical circulations (∼ 100 m). Second, the ARI weakened the horizontal diffusion of pollutants by reducing the westerly winds and enhancing wind convergence and southerly winds. Under these two mechanisms, pollutants could only recirculate in a limited space. This superposition of the typical local circulation and the ARI eventually contributed to the accumulation of pollutants and the consequent deterioration of haze pollution in the region.

An approach to refining the ground meteorological observation stations for improving PM2.5 forecasts in the Beijing–Tianjin–Hebei region

Abstract. This paper investigates how to refine the ground meteorological observation network to greatly improve the PM2.5 concentration forecasts by identifying sensitive areas for targeted observations that are associated with a total of 48 forecasts in eight heavy haze events during the years of 2016–2018 over the Beijing–Tianjin–Hebei (BTH) region. The conditional nonlinear optimal perturbation (CNOP) method is adopted to determine the sensitive area of the surface meteorological fields for each forecast, and a total of 48 CNOP-type errors are obtained including wind, temperature, and water vapor mixing ratio components. It is found that, although all the sensitive areas tend to locate within and/or around the BTH region, their specific distributions are dependent on the events and the start times of the forecasts. Based on these sensitive areas, the current ground meteorological stations within and around the BTH region are refined to form a cost-effective observation network, which makes the relevant PM2.5 forecasts starting from different initial times for varying events assimilate fewer observations, but overall, it achieve the forecasting skill comparable to and even higher than that obtained by assimilating all ground station observations. This network sheds light on the idea that some of the current ground stations within and around the BTH region are very useless for improving the PM2.5 forecasts in the BTH region and can be greatly scattered to avoid unnecessary work.

Secondary Formation of Atmospheric Brown Carbon in China Haze: Implication for an Enhancing Role of Ammonia.

Optical characteristics and molecular compositions of brown carbon (BrC) were investigated during winter 2019 at a rural site of China with a focus on nitro-aromatic compounds (NACs) and imidazoles (IMs). The abundance of gaseous nitrophenols relative to CO during the campaign maximized at noontime, being similar to O3, while the particulate NACs during the haze periods strongly correlated with toluene and NO2, suggesting that NACs in the region are largely formed from the gas-phase photooxidation. Strong correlations of particulate IMs in the dry haze periods with the mass ratio of EC/PM2.5 and the concentration of levoglucosan were observed, indicating that IMs during the dry events are largely derived from biomass burning emissions. However, an increase in IMs with the increasing aerosol liquid water content and pH was observed in the humid haze events, along with much lower abundances of levoglucosan and K+ relative to PM2.5, suggesting that IMs were mostly formed from aqueous reactions in the humid haze periods. These IMs exponentially increased with an increasing NH3 owing to an aqueous reaction of carbonyls with free ammonia. Our findings for the first time revealed an enhancing effect of ammonia on BrC formation in China, especially in humid haze periods.

Predicting Particulate Matter (PM10) during High Particulate Event (HPE) using Quantile Regression in Klang Valley, Malaysia

Particulate matter (PM10) is the key indicator of air quality index (API) during high particulate event (HPE). The presence of PM10 is believed to have an adverse effect on human health and environment. Therefore, the prediction of future PM10 concentration is very important because it can aid the local authorities to implement precautionary actions to limit the impact of air pollution. This study aims to compare the performances of two predictive models, which include Multiple Linear Regression (MLR) and Quantile Regression (QR) in predicting the next-day PM10 concentration during HPE. The hourly dataset of PM10 concentration with other trace gases and weather parameters at Kelang and Petaling Jaya from the year of historic haze event in Malaysia (1997, 2005, 2013 and 2015) were obtained from Department of Environment (DOE) Malaysia. Three performance measures namely Mean Absolute Error (MAE), Normalised Absolute Error (NAE) and Root Mean Squared Error (RMSE) were calculated to evaluate the performances of the predictive models. From the results, QR model at quantile 0.3 and 0.6 was chosen as the best predictive tools for predicting the next day PM10 concentration during haze event in Kelang and Petaling Jaya, respectively. showed better performance for the prediction of next-day PM10 concentration in Kelang. These results indicate that QR can be used as one of predictive tool to forecast air pollution concentration especially during unusual condition of air quality.

Modified linear regression for predicting ambient particulate pollutants (PM10) during High Particulate Event

Particulate Matter (PM10) is one of the most significant contributors towards haze or high particulate event (HPE) that occurs in Malaysia. HPE can severely affect human health, environment and economic so it is important to create a reliable prediction model in predicting future PM10 concentration especially during HPE. Therefore, the aim of this study is to investigate the performance of modified linear regression models in predicting the next-day Particulate Matter (PM10+24) concentration at two areas in the peninsular Malaysia namely, Bukit Rambai and Nilai. Hourly air quality dataset during historic HPE in 1997, 2005, 2013 and 2015 were used for analysis. Pearson correlation was used to select the input of the PM10 prediction model where only parameters with moderate (0.6 > r > 0.3) and strong (r > 0.6) correlation with PM10 concentration were selected as independent variables input in creating the multiple linear regression (MLR) model. The performance of modified linear regression model was evaluated by using several performance indicator which is Prediction Accuracy (PA), Index of Agreement (d 2), Root Mean Squared Error (RMSE) and Mean Absolute Error (MAE). The results show that the modified MLR (parameter with r > 0.6 included as input) gave the best prediction model for the next-day PM10 concentration in both Bukit Rambai and Nilai.

Measurement report: The 4-year variability and influence of the Winter Olympics and other special events on air quality in urban Beijing during wintertime

Abstract. Comprehensive measurements are vital to obtain big enough datasets for better understanding the complex atmosphere and further improving the air quality. To investigate the 4-year variation of air quality and the influences of special events (Beijing Winter Olympics, COVID lockdown and Chinese New Year) on it during the wintertime in polluted urban air, we conducted comprehensive observations in Beijing, China, during 1 January–20 February, in the years from 2019 to 2022. The mass concentration of PM2.5 and its composition (organics, nitrate, sulfate, ammonium, chloride and black carbon) and the number size distributions of particles (down to ∼1 nm) and ions, gaseous pollutants (CO, NOx, SO2, O3) and condensable vapors (sulfuric acid and oxygenated organic molecules), as well as meteorological parameters, were simultaneously measured. The days before 22 January without any special events in each year were selected to investigate the 4-year variability of air quality. We found that the concentrations of CO, NOx, total oxygenated organic molecules (OOMs), total PM2.5, organics, chloride and black carbon and the number concentration of sub-3 nm particles (N1.3−3) showed similar variations, decreasing from 2019 to 2021 and then increasing in 2022. For SO2, however, its concentration decreased year by year due to the significant emission reduction, further leading to the decrease of gaseous sulfuric acid and particulate sulfate from 2019 to 2022. O3 concentration showed an opposite 4-year variation compared with NOx. Meanwhile, both the oxygen and nitrogen contents of oxygenated organic molecules increased year by year, implying that not only the oxidation state of those compounds increased, but also NOx was involved more efficiently in their formation processes. With higher sulfuric acid concentrations and new particle formation (NPF) frequencies in 2021 than in 2022, and with the lowest concentrations of background aerosols and the lowest ambient temperatures in 2021, N1.3−3 was still the lowest in 2021. Unlike N1.3−3, the ion concentrations in both 0.8–2 and 2–4 nm size ranges were higher in 2021 than in the other years. Then, the days after 4 February were chosen to explore the influence of special events. The non-event days within this date range in 2019 and 2021 were chosen as the reference period. Due to the favorable meteorological conditions together with reductions in anthropogenic emissions, there were basically no haze events during the Olympics. Therefore, CO, NOx, SO2, total OOMs, accumulation-mode particles (N100−1000), and total PM2.5 and its composition were much lower, while ion concentrations were much higher compared with the reference period. Although there was also emission reduction during COVID, especially for NOx, the enhancement of secondary inorganic aerosol formation, together with unfavorable meteorological conditions, caused severe haze events during this period. Hence, CO, total OOMs and all PM2.5 compositions during COVID increased dramatically compared with the reference period. Influenced by SO2, condensation sink and sunlight, sulfuric acid concentration was found to be comparable between the Olympics and the reference period but was lower during COVID and Chinese New Year. Additionally, N1.3−3 was almost at the same level during different periods, indicating that the special events only had little impact on the NPF processes. These results provide useful information to the development of more targeted pollution control plans.

Significant contribution of carbonyls to atmospheric oxidation capacity (AOC) during the winter haze pollution over North China Plain

Atmospheric carbonyl compounds play significant roles in the cycling of radicals and have exhibited surprisingly high levels in winter that were well correlated to particulate matter, for which the reason have not been clearly elucidated. Here we measured carbonyl compounds and other trace gasses together with PM2.5 over urban Jinan in North China Plain during the winter. Markedly higher carbonyl concentrations (average: 14.63 ± 4.21 ppbv) were found during wintertime haze pollution, about one to three-times relative to those on non-haze days, with slight difference in chemical composition except formaldehyde (HCHO). HCHO (3.68 ppbv), acetone (3.17 ppbv), and acetaldehyde (CH3CHO) (2.83 ppbv) were the three most abundant species, accounting for ∼75% of the total carbonylson both haze and non-haze days. Results from observational-based model (OBM) with atmospheric oxidation capacity (AOC) indicated that AOC significantly increased with the increasing carbonyls during the winter haze events. Carbonyl photolysis have supplied key oxidants such as RO2 and HO2, and thereby enhancing the formation of fine particles and secondary organic aerosols, elucidating the observed haze-carbonyls inter-correlation. Diurnal variation with carbonyls exhibiting peak values at early-noon and night highlighted the combined contribution of both secondary formation and primary diesel-fuel sources. 1-butene was further confirmed to be the major precursor for HCHO. This study confirms the great contribution of carbonyls to AOC, and also suggests that reducing the emissions of carbonyls would be an effective way to mitigate haze pollution in urban area of the NCP region.

Variability of PM10 level with gaseous pollutants and meteorological parameters during episodic haze event in Malaysia: Domestic or solely transboundary factor?

Haze has become a seasonal phenomenon affecting Southeast Asia, including Malaysia, and has occurred almost every year within the last few decades. Air pollutants, specifically particulate matter, have drawn a lot of attention due to their adverse impact on human health. In this study, the spatial and temporal variability of the PM10 concentration at Kelang, Melaka, Pasir Gudang, and Petaling Jaya during historic haze events were analysed. An hourly dataset consisting of PM10, gaseous pollutants and weather parameters were obtained from Department of Environment Malaysia. The mean PM10 concentrations exceeded the stipulated Recommended Malaysia Ambient Air Quality Guideline for the yearly average of 150 μg/m3 except for Pasir Gudang in 1997 and 2005, and Petaling Jaya in 2013. The PM10 concentrations exhibit greater variability in the southwest monsoon and inter-monsoon periods at the studied year. The air masses are found to be originating from the region of Sumatra during the haze episodes. Strong to moderate correlation of PM10 concentrations was found between CO during the years that recorded episodic haze, meanwhile, the relationship of PM10 level with SO2 was found to be significant in 2013 with significant negatively correlated relative humidity. Weak correlation of PM10-NOx was measured in all study areas probably due to less contribution of domestic anthropogenic sources towards haze events in Malaysia.

Resolving the Formation Mechanism of HONO via Ammonia-Promoted Photosensitized Conversion of Monomeric NO2 on Urban Glass Surfaces

Understanding the formation processes of nitrous acid (HONO) is crucial due to its role as a primary source of hydroxyl radicals (OH) in the urban atmosphere and its involvement in haze events. In this study, we propose a new pathway for HONO formation via the UVA-light-promoted photosensitized conversion of nitrogen dioxide (NO2) in the presence of ammonia (NH3) and polycyclic aromatic hydrocarbons (PAHs, common compounds in urban grime). This new mechanism differs from the traditional mechanism, as it does not require the formation of the NO2 dimer. Instead, the enhanced electronic interaction between the UVA-light excited triplet state of PAHs and NO2-H2O/NO2-NH3-H2O significantly reduces the energy barrier and facilitates the exothermic formation of HONO from monomeric NO2. Furthermore, the performed experiments confirmed our theoretical findings and revealed that the synergistic effect from light-excited PAHs and NH3 boosts the HONO formation with determined HONO fluxes of 3.6 × 1010 molecules cm-2 s-1 at 60% relative humidity (RH) higher than any previously reported HONO fluxes. Intriguingly, light-induced NO2 to HONO conversion yield on authentic urban grime in presence of NH3 is unprecedented 130% at 60% RH due to the role of NH3 acting as a hydrogen carrier, facilitating the transfer of hydrogen from H2O to NO2. These results show that NH3-assisted UVA-light-induced NO2 to HONO conversion on urban surfaces can be a dominant source of HONO in the metropolitan area.

Applicability of the low-cost OPC-N3 optical particle counter for microphysical measurements of fog

Abstract. Low-cost devices for particulate matter measurements are characterised by small dimensions and a light weight. This advantage makes them ideal for UAV measurements, where those parameters are crucial. However, they also have some issues. The values of particulate matter from low-cost optical particle counters can be biased by high ambient humidity. In this article, we evaluate the low-cost Alphasense OPC-N3 optical particle counter for measuring the microphysical properties of fog. This study aimed to show that OPC-N3 not only registers aerosols or humidified aerosols but also registers fog droplets. The study was carried out on the rooftop of the Institute of Geophysics, University of Warsaw, Poland, during autumn–winter 2021. To validate the results, the data from OPC-N3 were compared with the data obtained from the reference instrument, the Oxford Lasers VisiSize D30. VisiSize D30 is a shadowgraph device able to register photos of individual droplets. Considering the effective radius of droplets, it is possible to differentiate low-visibility situations between fog conditions (which are not hazardous for people) from haze events, when highly polluted air can cause health risks to people. The compared microphysical properties were liquid water content (LWC), number concentration (Nc), effective radius reff and statistical moments of radius. The Pearson correlation coefficient between both devices for LWC was 0.92, Nc was 0.95 and reff was 0.63. Overall, these results suggest good compliance between instruments. However, the OPC-N3 has to be corrected regarding professional equipment.