Significant Biogenic Source of Oxygenated Volatile Organic Compounds and the Impacts on Photochemistry at a Regional Background Site in South China.

Oxygenated volatile organic compounds (OVOCs) significantly modulate atmospheric chemistry, but the sources and air quality impacts of OVOCs in aged urban outflows remain to be elucidated. At a background site in South China, the ozone formation potential of six nonformaldehyde OVOCs studied was equivalent to that of 3.56 ppbv of formaldehyde, more than half of which was contributed by acetaldehyde.

Wintertime ozone surges: The critical role of alkene ozonolysis.

Ozone (O) pollution is usually linked to warm weather and strong solar radiation, making it uncommon in cold winters. However, an unusual occurrence of four high O episode days (with maximum hourly concentrations exceeding 100 ppbv and peaking at 121 ppbv) was recorded in January 2018 in Lanzhou city, China. During these episodes, the average daytime concentration of total non-methane volatile organic compounds (TVOCs) reached 153.

Large-scale land-sea interactions extend ozone pollution duration in coastal cities along northern China.

Land-sea atmosphere interaction (LSAI) is one of the important processes affecting ozone (O) pollution in coastal areas. The effects of small-scale LSAIs like sea-land breezes have been widely studied. However, it is not fully clear how and to what extent the large-scale LSAIs affect O pollution.

Increased diurnal difference of NO concentrations and its impact on recent ozone pollution in eastern China in summer.

Nitrogen dioxide (NO) is a key tropospheric O precursor. Since 2013, efforts to decrease air pollution in China have driven substantial declines in annual NO concentrations, whereas ozone (O) concentrations have increased. Based on nationwide NO observations and a regional air quality model (WRF-CMAQ), we analyzed trends in the diurnal difference (DD, the difference between nighttime and daytime concentrations) of NO concentrations across eastern China and in five national urban agglomerations (UAs) from 2014 to 2021, and explored the factors underlying such changes and the potential impacts on O pollution.

Evidence for Reducing Volatile Organic Compounds to Improve Air Quality from Concurrent Observations and In Situ Simulations at 10 Stations in Eastern China.

Ground-level ozone (O) has been an emerging air pollution in China and interacts with fine particulate matters (PM). We synthesized observations of O and its precursors in two summer months of 2020 at 10 sites in the Zhejiang province, East China and simulated the in situ photochemistry. O pollution in the northeastern Zhejiang province was more serious than that in the southwest.

Does Ozone Pollution Share the Same Formation Mechanisms in the Bay Areas of China?

As important regions of transition between land and sea, the three bay areas of Bohai Bay (BHB), Hangzhou Bay (HZB), and Pearl River Estuary (PRE) in China often suffer from severe photochemical pollution despite scarce anthropogenic emissions. To understand the causes of high ozone (O) concentrations, the high O episode days associated with special synoptic systems in the three bays were identified via observations and simulated by the weather research and forecasting coupled with community multiscale air quality (WRF-CMAQ) model. It was revealed that the interaction between synoptic winds and mesoscale breezes resulted in slow wind speeds over the HZB and PRE, where air pollutants transported from upwind cities gained a long residence time and subsequently participated in intensive photochemical reactions.

Secondary organic aerosol formation at an urban background site on the coastline of South China: Precursors and aging processes.

Understanding the formation mechanisms of secondary organic aerosols (SOA) is an arduous task in atmospheric chemistry. In November 2018, a sampling campaign was conducted at an urban background site in Hong Kong for characterization of secondary air pollution. A high-resolution time-of-flight aerosol mass spectrometer was used to monitor the compositions of non-refractory submicron particulate matters (NR-PM), and multiple online instruments provided us with comprehensive auxiliary data.

Impact of NO reduction on long-term surface ozone pollution in roadside and suburban Hong Kong: Field measurements and model simulations.

Continuous measurements of ozone (O) and nitrogen oxides (NO = NO + NO) were conducted from 2007 to 2019 in Hong Kong in order to evaluate the effectiveness of control strategies for NO emission from diesel commercial vehicles (DCV). DCV control programs were periodically applied in three phases starting from 2007, 2010 and 2014. It was found that NO and NO levels decreased during the study period but more dramatically after the implementation of DCV Phase III than pre-DCV Phase III.

Emission characteristics, sources, and airborne fate of speciated organics in particulate matters in a Hong Kong residence.

A growing number of studies warn of the adverse health effects of indoor particulate matters (PM). However, little is known about the molecular compositions and emission characteristics of PM-bound organics (OM) indoors, a critical group of species with highest concentration and complexity in indoor PM. In a Hong Kong residence where prescribed activities were performed with normal frequency and intensity, we found that the activities significantly elevated not only the total concentration but also the fraction of OM in indoor PM.

Remarkable spring increase overwhelmed hard-earned autumn decrease in ozone pollution from 2005 to 2017 at a suburban site in Hong Kong, South China.

Ozone (O) pollution has been a persistent problem in Hong Kong, particularly in autumn when severe O pollution events are often observed. In this study, linear regression analyses of long-term O data in suburban Hong Kong revealed that the variation of autumn O obviously leveled off during 2005-2017, mainly due to the significant decrease of autumn O in 2013-2017 (period II), despite the increase in 2005-2012 (period I). In addition, the rise of O in summer and winter also ceased since 2013.

Photodissociation of particulate nitrate as a source of daytime tropospheric Cl.

Chlorine atoms (Cl) are highly reactive and can strongly influence the abundances of climate and air quality-relevant trace gases. Despite extensive research on molecular chlorine (Cl), a Cl precursor, in the polar atmosphere, its sources in other regions are still poorly understood. Here we report the daytime Cl concentrations of up to 1 ppbv observed in a coastal area of Hong Kong, revealing a large daytime source of Cl (2.

Photochemical ozone pollution in five Chinese megacities in summer 2018.

To investigate photochemical ozone (O) pollution in urban areas in China, O and its precursors and meteorological parameters were simultaneously measured in five megacities in China in summer 2018. Moderate wind speeds, strong solar radiation and high temperature were observed in all cities, indicating favorable meteorological conditions for local O formation. However, the unusually frequent precipitation caused by typhoons reaching the eastern coastline resulted in the least severe air pollution in Shanghai.

The state of science on severe air pollution episodes: Quantitative and qualitative analysis.

Severe episodic air pollution blankets entire cities and regions and have a profound impact on humans and their activities. We compiled daily fine particle (PM) data from 100 cities in five continents, investigated the trends of number, frequency, and duration of pollution episodes, and compared these with the baseline trend in air pollution. We showed that the factors contributing to these events are complex; however, long-term measures to abate emissions from all anthropogenic sources at all times is also the most efficient way to reduce the occurrence of severe air pollution events.

Real-time molecular characterization of air pollutants in a Hong Kong residence: Implication of indoor source emissions and heterogeneous chemistry.

Due to the high health risks associated with indoor air pollutants and long-term exposure, indoor air quality has received increasing attention. In this study, we put emphasis on the molecular composition, source emissions, and chemical aging of air pollutants in a residence with designed activities mimicking ordinary Hong Kong homes. More than 150 air pollutants were detected at molecular level, 87 of which were quantified at a time resolution of not less than 1 hour.

Long-term variations of C-C alkyl nitrates and their sources in Hong Kong.

Investigating the long-term trends of alkyl nitrates (RONO) is of great importance for evaluating the variations of photochemical pollution. Mixing ratios of C-C RONO were measured in autumn Hong Kong from 2002 to 2016, and the average level of 2-butyl nitrate (2-BuONO) always ranked first. The C-C RONO all showed increasing trends (p < 0.

Impact of weather and emission changes on NO concentrations in China during 2014-2019.

Nitrogen dioxide (NO) is one of the most important air pollutants that highly affect the formation of secondary fine particles and tropospheric ozone. In this study based on hourly NO observations from June 2014 to May 2019 and a regional air quality model (WRF-CMAQ), we comprehensively analyzed the spatiotemporal variations of NO concentrations throughout China and in 12 urban agglomerations (UAs) and quantitatively showed the anthropogenic and meteorological factors controlling the interannual variations (IAVs). The ground observations and tropospheric columns show that high NO concentrations are predominantly concentrated in UAs such as Beijing-Tianjin-Hebei (BTH), the Shandong Peninsula (SP), the Central Plain (CP), Central Shaanxi (CS), and the Yangtze River Delta (YRD).

Photochemistry of ozone pollution in autumn in Pearl River Estuary, South China.

To explore the photochemical O pollution over the Pearl River Estuary (PRE), intensive measurements of O and its precursors, including trace gases and volatile organic compounds (VOCs), were simultaneously conducted at a suburban site on the east bank of PRE (Tung Chung, TC) in Hong Kong and a rural site on the west bank (Qi'ao, QA) in Zhuhai, Guangdong in autumn 2016. Throughout the sampling period, 3 days with high O levels (maximum hourly O > 100 ppbv) were captured at both sites (pattern 1) and 13 days with O episodes occurred only at QA (pattern 2). It was found that O formation at TC was VOC-limited in both patterns because of the large local NO emissions.

In Situ Measurements of Molecular Markers Facilitate Understanding of Dynamic Sources of Atmospheric Organic Aerosols.

Reducing the amount of organic aerosol (OA) is crucial to mitigation of particulate pollution in China. We present time and air-origin dependent variations of OA markers and source contributions at a regionally urban background site in South China. The continental air contained primary OA markers indicative of source categories, such as levoglucosan, fatty acids, and oleic acid.

Hazardous volatile organic compounds in ambient air of China.

Volatile organic compounds (VOCs) are ubiquitous in the atmosphere and the majority of them have been proved to be detrimental to human health. The hazardous VOCs were studied very insufficiently in China, despite the enormous emissions of VOCs. In this study, the concentrations and sources of 17 hazardous VOCs reported in literature were reviewed, based on which the health effects were assessed.

Atmospheric fate of peroxyacetyl nitrate in suburban Hong Kong and its impact on local ozone pollution.

Peroxyacetyl nitrate (PAN) is an important reservoir of atmospheric nitrogen, modulating reactive nitrogen cycle and ozone (O) formation. To understand the origins of PAN, a field measurement was conducted at Tung Chung site (TC) in suburban Hong Kong from October to November 2016. The average level of PAN was 0.

Overview on the spatial-temporal characteristics of the ozone formation regime in China.

Ozone (O3), a main component in photochemical smog, is a secondary pollutant formed through complex photochemical reactions involving nitrogen oxides (NOx) and volatile organic compounds (VOCs). In the past few decades, with the rapid economic development, industrialization and urbanization, the mixing ratio of O3 has increased substantially in China. O3 non-attainment days have been frequently observed.

Aggravating O pollution due to NO emission control in eastern China.

During the past five years, China has witnessed a rapid drop of nitrogen oxides (NO) owing to the wildly-applied rigorous emission control strategies across the country. However, ozone (O) pollution was found to steadily deteriorate in most part of eastern China, especially in developed regions such as Jing-Jin-Ji (JJJ), Yangtze River Delta region (YRD) and Pearl River Delta region (PRD). To shed more light on current O pollution and its responses to precursor emissions, we integrate satellite retrievals, ground-based measurements together with regional numerical simulation in this study.

Photochemical evolution of continental air masses and their influence on ozone formation over the South China Sea.

To investigate photochemical ozone (O) pollution over the South China Sea (SCS), an intensive sampling campaign was conducted from August to November simultaneously at a continental site (Tung Chung, TC) and a marine site (Wan Shan Island, WSI). It was found that when continental air masses intruded the SCS, O episodes often occurred subsequently. To discover the causes, a photochemical trajectory model (PTM) coupled with the near-explicit Master Chemical Mechanism (MCM) was adopted, and the photochemical processes of air masses during the transport from TC to WSI were investigated.

Secondary Organic Aerosol Formation from Urban Roadside Air in Hong Kong.

Motor vehicle emissions are an important but poorly constrained source of secondary organic aerosol (SOA). Here, we investigated in situ SOA formation from urban roadside air in Hong Kong during winter time using an oxidation flow reactor (OFR), with equivalent atmospheric oxidation ranging from several hours to several days. The campaign-average mass enhancement of OA, nitrate, sulfate, and ammonium upon OFR aging was 7.

Continuous effectiveness of replacing catalytic converters on liquified petroleum gas-fueled vehicles in Hong Kong.

To mitigate the concentrations of air pollutants in the atmosphere, an intervention program of replacing the converters of liquefied petroleum gas (LPG) fueled vehicles was implemented by the Hong Kong government between October 2013 and April 2014. Data of ambient volatile organic compounds (VOCs) and other trace gases continuously monitored from September 2012 to April 2017 at a roadside site were used to evaluate the continuous effectiveness of the replaced catalytic converters on the reduction of air pollutants. The measurement data showed that LPG-related VOCs (propane and n/i-butanes) and several trace gases (CO, NO and NO) decreased significantly from before to after the program (p < 0.