Atmospheric Temperature Inversion Research Articles

Air Pollution and Respiratory Infectious Diseases

Recent research suggests that short-term exposure to air pollution is associated with an elevated prevalence of respiratory infectious disease. In this paper, we examine the relationship between the air quality index and weekly cases of COVID-19 and influenza-like illnesses (ILI) in the United States. We address potential bias from omitted variables and measurement error with an instrumental variable approach using atmospheric temperature inversions. Unlike other recent studies, we find no relationship between air quality and either COVID-19 or ILI cases.

Methane emission from a cool brown dwarf

Beyond our Solar System, aurorae have been inferred from radio observations of isolated brown dwarfs1,2. Within our Solar System, giant planets have auroral emission with signatures across the electromagnetic spectrum including infrared emission of H3+ and methane. Isolated brown dwarfs with auroral signatures in the radio have been searched for corresponding infrared features, but only null detections have been reported3. CWISEP J193518.59-154620.3. (W1935 for short) is an isolated brown dwarf with a temperature of approximately 482 K. Here we report James Webb Space Telescope observations of strong methane emission from W1935 at 3.326 μm. Atmospheric modelling leads us to conclude that a temperature inversion of approximately 300 K centred at 1–10 mbar replicates the feature. This represents an atmospheric temperature inversion for a Jupiter-like atmosphere without irradiation from a host star. A plausible explanation for the strong inversion is heating by auroral processes, although other internal and external dynamical processes cannot be ruled out. The best-fitting model rules out the contribution of H3+ emission, which is prominent in Solar System gas giants. However, this is consistent with rapid destruction of H3+ at the higher pressure where the W1935 emission originates4.

The relationship between atmospheric temperature inversion and urban air pollution characteristics: a case study of Tehran, Iran

This study conducts a comprehensive evaluation of air pollution in Tehran, focusing on its origins and potential remedial measures. Data from the Mehrabad station in Tehran were meticulously analyzed to scrutinize the spatiotemporal dynamics over a three-year period. Leveraging the Universal Radio Sound Observation (RAOB) program, we probed atmospheric attributes up to 750 m on specific critical dates: January 22, 2014; January 25, 2015; and November 27, 2016, which represent peak pollution events. Employing mathematical models, we scrutinized air temperature inversion profiles and applied the Heffter method to gauge the impact of atmospheric inversions on Tehran's air quality. Our investigation unequivocally identified January 25, 2015, as the most polluted date, unveiling precise atmospheric conditions during a radiation inversion, encompassing altitudes, temperatures, humidity, wind speed, and inversion depth. This research significantly advances our comprehension of the intricate interplay between atmospheric inversions and air pollution. It provides critical insights that can inform the development of targeted strategies to mitigate air quality issues not only in Tehran but also in analogous urban settings worldwide.

Interannual variability and trends of summertime PM2.5-based air quality in the Intermountain West

Summertime air quality is a growing public health concern in the populated region of Northern Utah. Whereas winter air pollution is highly linked with local atmospheric temperature inversions associated with upper atmospheric high-pressure and radiational cooling in valleys, the relationship between climate factors and the frequency of poor air quality during summer is still unknown. Analyzing the last 20 years of data, we demonstrated that summertime unhealthy days (as defined by PM2.5 air quality index level) in Northern Utah highly correlate with the number of dry-hot days, wildfire size, and an upper atmospheric ridge over the Northwestern United States. The persistent atmospheric ridge enhances lightning-caused fire burned areas in northwestern states and then transports the wildfire smoke toward Northern Utah. Similarly, climate model simulations confirm observational findings, such as an increasing trend of the upper atmospheric ridge and summertime dry days in the northwestern states. Such metrics developed in this study could be used to establish longer-term monitoring and seasonal forecasting for air quality and its compounding factors, which is currently limited to forecasting products for only several days.

Mach cutoff phenomenon of sonic boom in temperature inversion layers

The Mach cutoff of sonic boom occurs when shock waves propagate from supersonic to subsonic regions in a stratified atmosphere. In this study, numerical simulations are performed to clarify Mach cutoff behaviors in atmospheric temperature inversion layers, which have not yet been investigated. The two-dimensional Euler equations with a gravitational source term are solved in a horizontally stratified atmosphere. Surface and non-surface temperature inversion layers include three and four supersonic–subsonic mixing layers, respectively. Computations are made to analyze the propagation characteristics of a conventional N-shaped waveform. The results show that multiple upward and downward cutoffs occur owing to atmospheric temperature inversions, with multiple outgoing and evanescent waves, and multiple shock wave focusing. The upward and downward cutoffs act similarly. The positive- and negative-pressure regions are inversed when a cutoff occurs twice; thus, each cutoff shifts a phase by π/2, as expressed in the linear theory of caustics. A waveform transition occurs owing to wave splitting in a cutoff region, in addition to the phase shift. For surface temperature inversion, upward cutoffs make the waves between the cutoff and ground surfaces persist, resulting in rumbling. For non-surface temperature inversion, upward and downward cutoffs occur alternately, and the waves between them persist as well. Therefore, multiple cutoffs in temperature inversion layers play an important role in sonic boom evaluation during low supersonic flight.

Processing and Validation of the STAR COSMIC-2 Temperature and Water Vapor Profiles in the Neutral Atmosphere

The global navigation satellite system (GNSS) radio occultation (RO) is becoming an essential component of National Oceanic and Atmospheric Administration (NOAA) observation systems. The constellation observing system for meteorology, ionosphere, and climate (COSMIC) 2 mission and the Formosa satellite mission 7, a COSMIC follow-on mission, is now the NOAA’s backbone RO mission. The NOAA’s dedicated GNSS RO SAtellite processing and science Application Center (RO-SAAC) was established at the Center for Satellite Applications and Research (STAR). To better quantify how the observation uncertainty from clock error and geometry determination may propagate to bending angle and refractivity profiles, STAR has developed the GNSS RO data processing and validation system. This study describes the COSMIC-2 neutral atmospheric temperature and moisture profile inversion algorithms at STAR. We used RS41 and ERA5, and UCAR 1D-Var products (wetPrf2) to validate the accuracy and uncertainty of the STAR 1D-Var thermal profiles. The STAR-RS41 temperature differences are less than a few tenths of 1 K from 8 km to 30 km altitude with a standard deviation (std) of 1.5–2 K. The mean STAR-RS41 water vapor specific humidity difference and the standard deviation are −0.35 g/kg and 1.2 g/kg, respectively. We also used the 1D-Var-derived temperature and water vapor profiles to compute the simulated brightness temperature (BTs) for advanced technology microwave sounder (ATMS) and cross-track infrared sounder (CrIS) channels and compared them to the collocated ATMS and CrIS measurements. The BT differences of STAR COSMIC-2-simulated BTs relative to SNPP ATMS are less than 0.1 K over all ATMS channels.

Urban soils in a historically industrial city: patterns of trace metals in Pittsburgh, Pennsylvania

The distribution of legacy heavy metals in industrial city soils is not well documented. Therefore, fundamental details such as the ‘background’ (i.e., non-road/non-dripline) concentration of trace metals in urban soils are uncertain. While there has been a strong focus on mapping lead contamination near roads and residences, these studies are generally not placed in the context of the urban background. In this study, ‘background’ distributions of urban relevant trace metals: arsenic, cadmium, copper, lead, and zinc were mapped based on soil samples collected throughout Pittsburgh. Distinct spatial patterns were revealed: contamination is elevated in the eastern portion of the study area, driven by dominant wind patterns and historical coking activities in low-lying areas (paleochannels), areas subject to atmospheric temperature inversions that focus air contamination. The mixing analysis revealed spatial structures in contributions of industrial activities to metal soil contamination. In particular, regions enriched in cadmium relative to zinc (i.e., Zn:Cd<317) were located near historical coking operations, and areas enriched in lead relative to zinc (Pb:Zn>1) were located in areas with historical secondary lead smelters. These results suggest a comprehensive accounting of the trace metals concentrations in background soils has important implications for the assessment of exposure risk in populations residing in historically industrial areas. Relatively sparse sampling of background conditions in urban systems can indicate patterns of legacy contamination and attribute this contamination to historical sources.

The relationship between atmospheric boundary layer and temperature inversion layer and their aerosol capture capabilities

The vertical distribution of aerosols is an important factor in the study of urban environment pollution. However, whether the aerosol is captured by the atmospheric boundary layer or the temperature inversion layer remains unclear. In this study, the relationship between atmospheric boundary layer and temperature inversion layer was investigated based on the micropulse lidar and radiosonde measurements from February 2017 to September 2021 at atmospheric radiation measurement southern great plains site. The results revealed that for each residual layer height (RLH), stable boundary layer height (SBLH) and mixing layer height (MLH), the occurrence frequency of inversion layer within its 0.3 km range is 58, 58 and 68%, respectively. Moreover, the relative error of the MLH, RLH and SBLH relative to the inversion layer height (ILH) under different inversion strength (ΔT) conditions were investigated. The mean relative errors for MLH-ILH, RLH-ILH and SBLH-ILH are −4.13 ± 9.69, −2.26 ± 9.36 and −1.81 ± 15.87%, respectively. The result indicates that the ILH is generally higher than the top of the aerosol layer, and this phenomenon becomes more obvious as the ΔT increased. Finally, the aerosol capture capabilities of different layers are compared. The determination coefficient (R2) between AOD below RLH (MLH) and AOD below ILH are 0.47 (0.58). When the ΔT is larger than 2 °C, the R2 between AOD below RLH (MLH) and AOD below ILH has been obviously improved, increasing to 0.81 (0.90). By contrast, when the ΔT is smaller than 2 °C, the aerosol capture ability of RLH (MLH) is larger (smaller) than that of ILH. It indicates that the temperature inversion intensity is a key factor in determining the aerosol capture ability. These findings have implications for improving our understanding of the vertical distribution of aerosols and its controlling factors.

Impacts of meteorological parameters on the occurrence of air pollution episodes in the Sichuan basin

Episodes of fine-particulate matter (PM2.5) pollution are a widespread and common occurrence in China, and have potentially serious implications for human health. Meteorological conditions play an important role in air quality and influence the formation of regional air pollution episodes. This study applied a new classification method and daily PM2.5 concentration data to (a) evaluate different levels of air pollution in the Sichuan–Chongqing region between 2015 and 2017, and (b) investigate their relationships with meteorological parameters including atmospheric boundary layer height, wind speed, temperature inversion, weather type, and atmospheric transport. We identified a total of 40 air pollution episodes, the most severe of which occurred in winter when the atmospheric layer height was low. These heavy pollution events also coincided with low surface (10 m) wind speeds and temperature inversions, weather conditions that generally result from low pressure over the northwestern Sichuan Basin (90–102° E, 28–36° N) and southerly atmospheric transport.

Drone measurements of surface-based winter temperature inversions in the High Arctic at Eureka

Abstract. The absence of sunlight during the winter in the High Arctic results in a strong surface-based atmospheric temperature inversion, especially during clear skies and light surface wind conditions. The inversion suppresses turbulent heat transfer between the ground and the boundary layer. As a result, the difference between the surface air temperature, measured at a height of 2 m, and the ground skin temperature can exceed several degrees Celsius. Such inversions occur very frequently in polar regions, are of interest to understand the mechanisms responsible for surface–atmosphere heat, mass, and momentum exchanges, and are critical for satellite validation studies. In this paper we present the results of operations of two commercial remotely piloted aircraft systems, or drones, at the Polar Environment Atmospheric Research Laboratory, Eureka, Nunavut, Canada, at 80∘ N latitude. The drones are the Matrice 100 and Matrice 210 RTK quadcopters manufactured by DJI and were flown over Eureka during the February–March field campaigns in 2017 and 2020. They were equipped with a temperature measurement system built on a Raspberry Pi single-board computer, three platinum-wire temperature sensors, a Global Navigation Satellite System receiver, and a barometric altimeter. We demonstrate that the drones can be effectively used in the extremely challenging High Arctic conditions to measure vertical temperature profiles up to 75 m above the ground and sea ice surface at ambient temperatures down to −46 ∘C. Our results indicate that the inversion lapse rates within the 0–10 m altitude range above the ground can reach values of ∼ 10–30 ∘C(100m)-1 (∼ 100–300 ∘Ckm-1). The results are in good agreement with the coincident surface air temperatures measured at 2, 6, and 10 m levels at the National Oceanic and Atmospheric Administration flux tower at the Polar Environment Atmospheric Research Laboratory. Above 10 m more gradual inversion with order-of-magnitude smaller lapse rates is recorded by the drone. This inversion lapse rate agrees well with the results obtained from the radiosonde temperature measurements. Above the sea ice drone temperature profiles are found to have an isothermal layer above a surface-based layer of instability, which is attributed to the heat flux through the sea ice. With the drones we were able to evaluate the influence of local topography on the surface-based inversion structure above the ground and to measure extremely cold temperatures of air that can pool in topographic depressions. The unique technical challenges of conducting drone campaigns in the winter High Arctic are highlighted in the paper.

Impacts of Extreme Air Pollution Meteorology on Air Quality in China

AbstractExtreme air pollution meteorological events (EAPMEs), such as atmospheric stagnation (AS), heat wave (HW), and temperature inversion, significantly affect regional air quality. In the present study, considerably increased EAPME frequency with clear spatial variations is identified in China from 1960 to 2019. Strong air quality sensitivities to EAPMEs are identified by combing air quality and meteorological observations. We found that HW greatly affects ozone concentration and may enhance the generation of fine particles. AS showed a noticeable but opposite impact on fine particle pollution between northern and southern China owing to the wintertime heating policy. EAPMEs may increase the probability of air pollution for pollution levels greater than 2. For example, the synthetic effects of multiple EAPMEs could increase the probability of summer ozone and winter fine particle pollution in China by factors of up to 5 and 2, respectively. Based on such information, more attention may be needed on the collaborative prediction of extreme meteorological events and air pollution episodes.

Atmospheric Temperature Inversions and He i 5876 Core Profile Structure in White Dwarfs

Abstract We report distinctive core profiles in the strongest optical helium line, He i λ5876, from high-resolution high-sensitivity observations of spectral type DB white dwarfs. By analyzing a sample of 40 stars from Keck/HIRES and VLT/UVES, we find the core appearance to be related to the degree of hydrogen and heavy element content in the atmosphere. New Ca K-line measurements or upper limits are reported for about half the sample stars. He i λ5876 emission cores with a self-reversed central component are present for those stars with relatively low hydrogen abundance, as well as relatively low atmospheric heavy element pollution. This self-reversed structure disappears for stars with higher degrees of pollution and/or hydrogen abundance, giving way to a single absorption core. From our model atmospheres, we show that the self-reversed emission cores can be explained by temperature inversions in the upper atmosphere. We propose that the transition to a single absorption core is due to the additional opacity from hydrogen and heavy elements that inhibits the temperature inversions. Our current models do not exactly match the effective temperature range of the phenomenon or the amplitude of the self-reversed structure, which is possibly a result of missing physics such as 3D treatment, convective overshoot, and/or non-LTE effects. The He i λ5876 line structure may prove to be a useful new diagnostic for calibrating temperature profiles in DB atmosphere models.

A 17-year climatology of temperature inversions above clouds over the ARM SGP site: The roles of cloud radiative effects

Abstract Atmospheric temperature inversions, i.e., temperatures increasing with altitude, modulate both radiative and buoyancy fluxes in the atmosphere. A temperature inversion layer often occurs immediately above a cloud layer that cools radiatively and thereby strengthens the capping temperature inversion. This study aims to investigate the characteristics of temperature inversions above clouds and their relationships with cloud-top radiative cooling. Using a 17-year (January 2001 to December 2017) high-quality and continuous radiosonde dataset collected at the Atmospheric Radiation Measurement Southern Great Plains Central Facility site, key temperature inversion parameters, namely, the occurrence frequency (dp), depth (dz), temperature difference (dT), and gradient (dT/dz), are derived for single- and double-layer clouds (SLC and DLC, respectively). The occurrence frequency of temperature inversions above single-layer clouds decreases dramatically as cloud tops rise from low to high altitudes. When an overlying higher cloud layer is present, the inversion becomes less frequent, shallower, and weaker than without it. This may be because higher clouds weaken the cloud-top radiative cooling of the underneath clouds by enhancing downwelling infrared radiation. This is supported by radiative transfer simulations. There are distinctive seasonal cycles of cloud-top radiative cooling for high clouds that are primarily driven by variations in shortwave heating. Distinctive seasonal cycles of temperature inversions also occurred regardless of the cloud regime (SLC or DLC) and altitude (low or high clouds). They appear to be driven by the seasonal cycle of cloud coverage (i.e., a greater amount of clouds undergoes stronger area-mean radiative cooling) although the shortwave heating seasonal cycle also plays a role for high clouds. Cloud radiative cooling cannot explain the diurnal cycle of temperature inversions.

Estimating the effect of air pollution on road safety using atmospheric temperature inversions

Does air quality influence road safety? We estimate the effect of increased air pollution on the number of road traffic accidents in the United Kingdom between 2009 and 2014. To address concerns of spurious correlation we exploit atmospheric temperature inversions as a source of plausibly exogenous variation in daily air pollution levels. We find an increase of 0.3–0.6% in the number of vehicles involved in accidents per day for each additional 1 μg/m3 of PM2.5. The finding suggests that less safe roads may present a large and previously overlooked cost of air pollution. The results are robust to a number of specifications and across various sub-samples.

Optimization design of the tuning method for FBG spectroscopy based on the numerical analysis of all-fiber Raman temperature lidar

Abstract All fiber Raman temperature lidar for space borne platform has been proposed for profiling of the temperature with high accuracy. Fiber Bragg grating (FBG) is proposed as the spectroscopic system of Raman lidar because of good wavelength selectivity, high spectral resolution and high out-of-band rejection rate. Two sets of FBGs at visible wavelength 532 nm as Raman spectroscopy system are designed for extracting the rotational Raman spectra of atmospheric molecules, which intensities depend on the atmospheric temperature. The optimization design of the tuning method of an all-fiber rotational Raman spectroscopy system is analyzed and tested for estimating the potential temperature inversion error caused by the instability of FBG. The cantilever structure with temperature control device is designed to realize the tuning and stabilization of the central wavelengths of FBGs. According to numerical calculation of FBG and finite element analysis of the cantilever structure, the center wavelength offset of FBG is 11.03 nm/°C with the temperature change in the spectroscopy system. By experimental observation, the center wavelength offset of surface-bonded FBG is 9.80 nm/°C with temperature changing when subjected to certain strain for the high quantum number channel, while 10.01 nm/°C for the low quantum number channel. The tunable wavelength range of FBG is from 528.707 nm to 529.014 nm for the high quantum number channel and from 530.226 nm to 530.547 nm for the low quantum number channel. The temperature control accuracy of the FBG spectroscopy system is up to 0.03 °C, the corresponding potential atmospheric temperature inversion error is 0.04 K based on the numerical analysis of all-fiber Raman temperature lidar. The fine tuning and stabilization of the FBG wavelength realize the elaborate spectroscope of Raman lidar system. The conclusion is of great significance for the application of FBG spectroscopy system for space-borne platform Raman lidar.

Drag Produced by Waves Trapped at a Density Interface in Nonhydrostatic Flow over an Axisymmetric Hill

Abstract Linear nonhydrostatic theory is used to evaluate the drag produced by 3D trapped lee waves forced by an axisymmetric hill at a density interface. These waves occur at atmospheric temperature inversions, for example, at the top of the boundary layer, and contribute to low-level drag possibly misrepresented as turbulent form drag in large-scale numerical models. Unlike in 2D waves, the drag has contributions from a continuous range of wavenumbers forced by the topography, because the waves can vary their angle of incidence to match the resonance condition. This leads to nonzero drag for Froude numbers (Fr) both &amp;lt;1 and &amp;gt;1 and a drag maximum typically for Fr slightly below 1, with lower magnitude than in hydrostatic conditions owing to wave dispersion. These features are in good agreement with laboratory experiments using two axisymmetric obstacles, particularly for the lower obstacle, if the effects of a rigid lid above the upper layer and friction are taken into account. Quantitative agreement is less satisfactory for the higher obstacle, as flow nonlinearity increases. However, even in that case the model still largely outperforms both 3D hydrostatic and 2D nonhydrostatic theories, emphasizing the importance of both 3D and nonhydrostatic effects. The associated wave signatures are dominated by transverse waves for Fr lower than at the drag maximum, a dispersive “Kelvin ship-wave” pattern near the maximum, and divergent waves for Fr beyond the maximum. The minimum elevation at the density-interface depression existing immediately downstream of the obstacle is significantly correlated with the drag magnitude.

The Role of Emissivity in the Detection of Arctic Night Clouds

Detection of clouds over polar areas from satellite radiometric measurements in the visible and IR atmospheric window region is rather difficult because of the high albedo of snow, possible ice covered surfaces, very low humidity, and the usual presence of atmospheric temperature inversion. Cold and highly reflective polar surfaces provide little thermal and visible contrast between clouds and the background surface. Moreover, due to the presence of temperature inversion, clouds are not always identifiable as being colder than the background. In addition, low humidity often causes polar clouds to be optically thin. Finally, polar clouds are usually composed of a mixture of ice and water, which leads to an unclear spectral signature. Single and bi-spectral threshold methods are sometimes inappropriate due to a large variability of surface emissivity and cloud conditions. The objective of this study is to demonstrate the crucial role played by surface emissivity in the detection of polar winter clouds and the potential improvement offered by infrared hyperspectral observations, such as from the Infrared Atmospheric Sounding Interferometer (IASI). In this paper a new approach for cloud detection is proposed and validated exploiting active measurements from satellite sensors, i.e., the CloudSat cloud profiling radar (CPR) and the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) on board the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO). For a homogenous IASI field of view (FOVs), the proposed cloud detection scheme tallies with the combined CPR and CALIOP product in classifying 98.11% of the FOVs as cloudy and also classifies 97.54% of the FOVs as clear. The Hansen Kuipers discriminant reaches 0.95.

Characterization of methane plumes downwind of natural gas compressor stations in Pennsylvania and New York.

The extraction of unconventional oil and natural gas from shale energy reservoirs has raised concerns regarding upstream and midstream activities and their potential impacts on air quality. Here we present in situ measurements of ambient methane concentrations near multiple natural gas compressor stations in New York and Pennsylvania using cavity ring-down laser spectrometry coupled with global positioning system technology. These data reveal discernible methane plumes located proximally to compressor stations, which exhibit high variability in their methane emissions depending on the weather conditions and on-site activities. During atmospheric temperature inversions, when near-ground mixing of the atmosphere is limited or does not occur, residents and properties located within 1 mile of a compressor station can be exposed to rogue methane from these point sources. These data provide important insight into the characterization and potential for optimization of natural gas compressor station operations.

‘Warm’ Tundra: Atmospheric and Near‐Surface Ground Temperature Inversions Across an Alpine Treeline in Continuous Permafrost, Western Arctic, Canada

AbstractPermafrost conditions were examined between 2010 and 2014 at four sites across an alpine treeline on Peel Plateau, Northwest Territories, Canada. Ground and air temperature sensors were installed in forest and tundra between 30 and 500 m asl. Annual mean air temperatures increased and the number of freezing degree days declined with elevation, due to persistent winter air temperature inversions. The annual mean temperature at the permafrost surface (Tps) in mineral soils increased with elevation from about −2.5 °C in lowland forest to about −1.5 °C in dwarf shrub tundra. The increase in Tps coincided with higher air temperatures and earlier snow accumulation at tundra sites. The higher Tps in alpine tundra compared to lowland forest in Peel Plain contrasts with the northward decrease in Tps across latitudinal treeline elsewhere in the western Arctic. An increase in Tps with elevation may be common in Arctic mountain environments due to the prevalence of atmospheric temperature inversions in winter. In such contexts, although vegetation characteristics are governed by summer climate, permafrost conditions are critically influenced by the winter regime. The tundra permafrost on Peel Plateau is considerably warmer and, hence, more sensitive to disturbance than perennially frozen ground north of treeline in other parts of the western Arctic. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Analysis of diurnal variability of atmospheric halocarbons and CFC replacements to imply emission strength and sources at an urban site of Lukang in central Taiwan

Hourly atmospheric measurements of halocarbons and chlorofluorocarbon (CFC) replacements were conducted at an urban site of Lukang, Changhua, in central Taiwan from May to August, 2013. The temporal distribution of different groups of halocarbons in the Lukang urban atmosphere, including chlorofluorocarbons (CFCs), Chlorodifluoromethane (HCFC-22), Bromochlorodifluoromethane (Halon-1211), and other chlorinated compounds, is presented and discussed. The concentrations (mixing ratios) of HCFC-22, Dichlorodifluoromethane (CFC-12), Halon-1211, Trichlorofluoromethane (CFC-11), Dichloromethane (CH2Cl2), and Trichloroethylene (TCE) were enhanced with respect to the local background levels; the atmospheric mixing ratio of carbon tetrachloride (CCl4) was slightly higher than its local background level; on the other hand, 1,1,2-Trichlorotrifluoroethane (CFC-113) was relatively uniform and not very different from background atmospheric level in non-urban areas. Among these compounds, HCFC-22, Halon-1211 and the halogenated compounds, CH2Cl2 and TCE, used as solvents were strongly enhanced. The average mixing ratio of Halon-1211 was higher than the local background of ∼4.5 ppt by ∼60% although Halon-1211 production had been phased out by 1996.Hourly average mixing ratios of halocarbons (HCFC-22, CFC-12, Halon-1211, CFC-11, CH2Cl2, and TCE) illustrated a distinct diurnal cycle characterized with a pattern of elevated mixing ratio and large mixing ratio variability amplitude at night relative to that in daytime. Although emission sources of these halocarbons were complex, hourly average mixing ratios for most of these high variability halocarbons peaked at ∼5:00 AM when the hourly average wind speed reached the minimum value of the day; by contrast, the hourly average mixing ratio of CO peaked at ∼8:30 AM when the ambient atmospheric wind condition was strongly influenced by sea breezes during the traffic rush hours. This phenomenon revealed that meteorological factors predominated the distribution of halocarbon mixing ratio in the urban atmosphere and the traffic emission of CFC-12 derived from old vehicles manufactured before 1994 was insignificant to the CFC-12 mixing ratio in the urban atmosphere. The meteorological condition of nighttime atmospheric temperature inversion and low wind speed facilitated the accumulation of terrestrial airborne pollutants near the ground; consequently the hourly average mixing ratios at night were higher than those in daytime by up to ∼2% (CFC-11), ∼7% (CFC-12), ∼75% (HCFC-22), ∼72% (Halon-1211), ∼280% (CH2Cl2), and ∼155% (TCE).