Mixing Layer Height Research Articles

Quantifying aircraft emissions of Shanghai Pudong International Airport with aircraft ground operational data

The air traffic growth at Shanghai Pudong International Airport (PVG) has attracted much concern over the potential impacts on local air quality and human health; however, the emission contributions due to aircraft activities, impact on air quality and health effects remain unclear. In this study, the ground operational data derived from the Aircraft Communication Addressing and Reporting System (ACARS) dataset are newly utilized to obtain the PVG-specific emission parameters of 10 distinct aircraft-engine combinations during the taxi-in and taxi-out phases of the landing and take-off (LTO) cycle. The resulting emission parameters, together with PVG-specific operational conditions, are applied to quantify the annual emissions in 2017 for main engines and auxiliary power units (APUs) at PVG, emission variations caused by mixing layer height, sensitivity of black carbon (BC) emissions to the estimation method and sensitivity of PM2.5 emissions to the fuel sulfur content (FSC). The results show noticeable discrepancies between the corrected fuel flows and NOx emission indices (EIs) and those certified by the International Civil Aviation Organization (ICAO). The annual emissions of hydrocarbons (HC), CO, NOx, NO, NO2, HONO, HNO3, NOy, SO2, SO42−, BC, organic carbon (OC) and PM2.5 with corrected emission parameters are 3.82 × 105 kg, 4.35 × 106 kg, 5.36 × 106 kg, 4.40 × 106 kg, 9.58 × 105 kg, 1.03 × 105 kg, 3.83 × 103 kg, 5.47 × 106 kg, 3.56 × 105 kg, 1.31 × 104 kg, 5.43 × 104 kg, 4.73 × 103 kg and 7.22 × 104 kg, respectively, while the application of the maximum height of the mixing layer contributes to emission increases as high as 16.9% (NOx). An alternative estimation of BC emissions leads to an increase of 50% compared with first-order approximation 3 (FOA3), while a reduction in PM2.5 emissions can be expected by minimizing the FSC.

Characteristics of Aerosol Particulate Concentrations and Their Climate Background in Shanghai During 2007-2016

We use daily aerosol particulate matter<10 μm (PM10) concentration data from 2006 to 2016 in Shanghai along with meteorological elements (wind and temperature), atmospheric stability, temperature inversion, and upper atmosphere circulation data, to analyze the variation characteristics of the PM10 concentrations and differences of the winter climate background. We establish a multivariate linear stepwise regression equation, and also compare and analyze differences in the upper atmospheric circulation by selecting the years with the highest and lowest PM10 concentrations. The results showed an oscillating downward trend in the annual average concentrations of PM10 in Shanghai, whereas seasonally, PM10 concentrations were relatively high in winter and showed two peaks with a low in between. PM10 concentrations were negatively correlated with the daily average wind speed and the daily mixing layer height at 20:00, and positively correlated with the frequency of northwest wind, the mean daily temperature, and the frequency of stable weathers and thermal inversion at 20:00. When the 500 hPa height field in the northern part of China was a positive anomaly in winter, a warm winter prevailed and led to high PM10 concentrations. When the 500 hPa height field was a negative anomaly, cold air frequently moved southward to result in relatively low temperatures, which caused relatively low PM10 concentrations. When the wind field at 850 hPa was easterly, the wind speed was relatively large and resulted in relatively low PM10 concentrations.

Estimating the remaining atmospheric environmental capacity using a single-box model in a high pollution risk suburb of Chengdu, China

The atmospheric pollution has been the public attention in recent years. In order to better coordinate economic development and atmospheric environmental management, China introduced the concept of atmospheric environmental capacity (AEC). The remaining atmospheric environmental capacity (RAEC) calculated by existing atmospheric pollution sources and AEC is an important basis for regional development and environmental protection. The RAEC of the high-pollution risk suburb of Chengdu in 2015 was estimated by the single-box model and analyzed on multiple time scales. The results show that the RAEC of SO2 and NO2 in this region is 3299 t/a and 2849 t/a, respectively under the annual time scale. However, in the daily time scale, the RAEC of NO2 is negative for 3 days, that is, there are 3 days with serious air pollution. Therefore, it is not appropriate to plan the industrial area only by relying on annual RAEC. Especially, RAEC displays inter-seasonal and monthly variability. On the one hand, in plain areas with low wind speed and little change in wind direction, achieving the prediction of atmospheric mixing layer height could give early warning of atmospheric pollution events. On the other hand, different management measures are taken on different time scales. On a long timescale, the regional energy structure should be optimized. On seasonal and monthly time scales, the production plans should be adapted to RAEC. On the daily time scale, it mainly deals with the serious atmospheric pollution accident timely.

Entrainment and Mixing of Transported Ozone Layers: Implications for Surface Air Quality in the Western U.S.

Recently, two air quality campaigns were conducted in the southwestern United States to study the impact of transported ozone, stratospheric intrusions, and fire emissions on ground-level ozone concentrations. The California Baseline Ozone Transport Study (CABOTS) took place in May – August 2016 covering the central California coast and San Joaquin Valley, and the Fires, Asian, and Stratospheric Transport Las Vegas Ozone Study (FAST-LVOS) was conducted in the greater Las Vegas, Nevada area in May – June 2017. During these studies, nearly 1000 hours of ozone and aerosol profile data were collected with the NOAA TOPAZ lidar. A Doppler wind lidar and a radar wind profiler provided continuous observations of atmospheric turbulence, horizontal winds, and mixed layer height. These measurements allowed us to directly observe the degree to which ozone transport layers aloft were entrained into the boundary layer and to quantify the resulting impact on surface ozone levels. Mixed layer heights in the San Joaquin Valley during CABOTS were generally below 1 km above ground level (AGL), while boundary layer heights in Las Vegas during FAST-LVOS routinely exceeded 3 km AGL and occasionally reached up to 4.5 km AGL. Consequently, boundary layer entrainment was more often observed during FAST-LVOS, while most elevated ozone layers passed untapped over the San Joaquin Valley during CABOTS.

Variation Characteristics of Mass Concentration of Inhalable Particles in Qingdao, China

The geographical condition of Qingdao, China is relatively special; the transport of various inland pollutants, the emissions of marine aerosol and local pollutants will have an impact on the changes of atmospheric aerosol concentration. By using the stability classification method, trajectory clustering analysis and the NOAA HYSPLIT model, the seasonal distribution characteristics of atmospheric inhalable particulate matter concentration in Qingdao, China and its relationship with meteorological conditions, mixed layer height, and the seasonal characteristics of Qingdao pollutant transport were analyzed. The results show that the variation trends of PM2.5 and PM10 were about the same, and there are obvious seasonal differences, which are high in winter and spring, and low in summer and autumn. The concentration of inhalable particulate matter has a negative correlation with temperature, wind speed and relative humidity. The concentration of inhalable particulate matter is distinct in different relative humidity ranges. When the wind speed is less than 3 - 4 m/s, there are more inhalable particles, while the mass concentration shows obvious reduction with the wind speed more than 4 m/s. There is a significant negative correlation between the mass concentration of pollutants and the daily maximum mixed layer height. The larger the concentration of pollutants, the smaller the thickness of the daily largest mixed layer. Conversely, the smaller the mass concentration of pollutants, the larger the thickness of the daily largest mixed layer. The pollutant transport in Qingdao has obvious seasonal characteristics. The air mass in spring, autumn and winter is mainly medium-long distance transport from Mongolia and southern Russia, and medium-short distance transport from Inner Mongolia and northeast of China. The source of air masses in summer is mainly transported from the eastern and sea areas.

Modeling air quality in the San Joaquin valley of California during the 2013 Discover-AQ field campaign

Abstract The San Joaquin Valley (SJV) of California has one of the nation's most severe wintertime PM2.5 pollution problems. The DISCOVER-AQ (Deriving Information on Surface Conditions from Column and Vertically Resolved Observations Relevant to Air Quality) field campaign took place in the SJV from January 16 to February 6, 2013. It captured two PM2.5 pollution episodes with peak 24-h concentrations approaching 70 μg/m3. Using meteorological fields generated from WRFv3.6, CMAQv5.0.2 was applied to simulate PM2.5 formation in the SJV from January 10 through February 10, 2013. Overall, the model was able to capture the observed accumulation of PM2.5 within the simulation period. The model was able to produce increased concentrations of ammonium nitrate and organic carbon, which are two major components of wintertime PM2.5 in the SJV. Comparison to measurements made by aircraft showed that there was general agreement between observed and modeled daytime vertical distributions of selected gas and particulate species, reflecting the adequacy of modeled daytime mixing layer heights. Excess ammonia predicted by the model implied that ammonium nitrate formation was limited by the availability of nitric acid, consistent with observations. Evaluation of the ammonium nitrate diurnal profile revealed that the observed morning increase of ammonium nitrate was also evident from the model. This paper demonstrates that the CMAQ model is able to simulate elevated wintertime PM2.5 formation observed in the SJV during the DISCOVER-AQ 2013 period, which featured both climatic (i.e., 2011–2014 California Drought) and emissions differences compared to a previous large air quality field campaign in the SJV during 1999–2000.

Study on conceptual model of regional pollution meteorological conditions in Guanzhong Urban Agglomeration

This paper defined regional pollution day and regional heavy pollution day, calculated the atmospheric stability by Pasqual classification and the height of mixed layer by national standard method, established a conceptual model of meteorological conditions in Guanzhong Urban Agglomeration. The results show that：(1) The more possibility of the regional pollution and regional heavy pollution is, the lower the mixing layer height is. (2)The frequency of stability increased with degree of pollution, the frequency of regional heavy pollution stability reached nearly 60% as regional heavy pollution. (3)In heavily polluted area, the frequency of ground temperature inversion is nearly 90%, the average cumulative temperature inversion thickness is 260m at assurance rate of 80%, and the maximum temperature inversion strength is 10.8℃/100m. (4) Regional pollution is easy to occur when the frequency of quiet wind is higher than 50%. At the same time, it is easy to form wind convergence area in the hinterland of Guanzhong Area, which causes the accumulation of pollutants.

Mathematical Model for Studying the Effect of the Atmospheric ‎Boundary Layer on the Surface Ozone Variations at a Coastal ‎Site

Atmospheric Boundary Layer (ABL) height (h) is one of the basic criteria ‎for describing its structure. ABL measurements, parameters and predictions have ‎numerous practical and theoretical implementations as forecast of pollutant ‎concentrations, surface temperature, expansion of disturbance measurements or ‎in climate models and numerical weather prediction. The height of mixing layer ‎is difficult to be measured; therefore, mathematical methods are introduced to ‎calculate this layer and different FORTRAN programs have been developed to ‎define the height of ABL on hourly basis per year. The analysis of the results ‎showed that the variation of the height of the mixing layer for different seasons ‎depends on the type of the dominant stability class and the value of wind speed, ‎where the rise of the mixing layer in winter and autumn months may be referred ‎to increased frequency of stability conditions in the unstable and slightly ‎unstable atmosphere On the other hand, when the stable conditions are dominant, ‎the height of the mixing layer remains smaller. ‎ The boundary layer ozone is a standard contaminant because of its ‎harmful effects on living organisms and plants. It also has an active role in ‎atmospheric chemistry and climate change; therefore, monthly and seasonal ‎variation of the surface ozone O3 concentration and its effects on the ‎atmospheric boundary layer measured for the first time at coastal site in Egypt at ‎the period 2013.‎

Mixing layer height estimated from AMDAR and its relationship with PMs and meteorological parameters in two cities in North China during 2014–2017

The mixing layer height (MLH) plays an important role in atmospheric pollution by influencing the vertical diffusion of pollutants. The Aircraft Meteorological Data Relay (AMDAR) from the airports in Beijing (BJ) and Shijiazhuang (SJZ) during 2014–2017 was used to investigate temporal characteristics of the daily maximum MLH (MLHmax) and their relationships with surface meteorological parameters and particulate matters (PM1, PM2.5, and PM10).The seasonal mean of MLHmax in BJ was higher than that of SJZ, and shows the seasonal variation trend of summer> spring >autumn > winter in both cities. The MLHmax was found to have a positive correlation with daily average wind speed at 2 m (WS) in all seasons except summer and a significant negative correlation with daily average relative humidity at 2 m (RH) in four seasons. These implied a high risk of air pollution during low-MLHmax period. Subsequently, a higher negative relationship between MLHmax and PMs was obtained in both cities in autumn and winter based on the polynomial regression method, with a coefficient of determination (R2) of 0.37–0.71 in autumn and 0.52–0.88 in winter. In BJ, the sequence of R2 was PM1 >PM2.5 >PM10, yet a total opposite trend was observed in SJZ. It illustrated that the greatest contribution to local emissions in BJ and SJZ is PM1 and PM10 respectively, which means that the impact of MLHmax to local emissions and the secondary formed pollutants is stronger than that of long range transport. The ammoniate (NH4+), nitrate (NO3−) and sulfate (SO42−) also performed a better correlation with MLHmax than elemental carbon (EC) and organic carbon (OC) in BJ; while in SJZ, a better correlation between MLHmax and EC is easy to be found, while NO3− and SO42− performed a worse correlation with it. Therefore, PM pollution was characterized by secondary formation in BJ but by primary emissions in SJZ.

Mixing Layer Height Retrievals From MiniMPL Measurements in the Chiang Mai Valley: Implications for Particulate Matter Pollution

Urbanized mountain valleys are usually prone to episodes of high concentrations of air pollutants due to the strong interplay between mountain meteorology and synoptic weather conditions. The mountain valley of Chiang Mai is engulfed by air pollutants with particulate matter (PM) concentration remaining above 50 µg m-3 (PM2.5, 24-hour average) during approximately 13 % days every year (mostly during February to April). This study presents the first time continuous measurements of mini- micro pulse LiDAR (MiniMPL) installed on the valley floor of Chiang Mai, providing vertical backscatter profile of aerosols and clouds from April 2017 onwards. This paper analyzes unique dataset of mixing layer (ML) height measurements made during April 2017 to June 2018 with a temporal resolution of 15 minutes. The ML height derived from the backscatter profile measurements are analyzed to understand the annual, monthly and diurnal variations. The ML height depicts distinct diurnal variations for all months of the year, evolving up to < 3.0 km during April to September. From October onwards the ML evolution is gradually inhibited, reducing to < 2.0 km during October to December and < 1.5 km during January to March. The variations in the concentration of PM were found to be partly modulated by the ML variations (Pearson coefficient ≈ −0.50) during dry season (February, March and April), possibly triggering the aerosol-boundary layer feedback mechanism for high concentrations (100 µg m-3) of PM and low ventilation in the valley. The inhibition of ML evolution due to feedback mechanism further escalates the high concentrations of PM, resulting in severe haze conditions on many days during the dry season.

Long-term brown carbon spectral characteristics in a Mediterranean city (Athens)

This study analyses 4-years of continuous 7-λ Aethalometer (AE-33) measurements in an urban-background environment of Athens, to resolve the spectral absorption coefficients (babs) for black carbon (BC) and brown carbon (BrC). An important BrC contribution (23.7 ± 11.6%) to the total babs at 370 nm is estimated for the period May 2015–April 2019, characterized by a remarkable seasonality with winter maximum (33.5 ± 13.6%) and summer minimum (18.5 ± 8.1%), while at longer wavelengths the BrC contribution is significantly reduced (6.8 ± 3.6% at 660 nm). The wavelength dependence of the total babs gives an annual-mean AAE370-880 of 1.31, with higher values in winter night-time. The BrC absorption and its contribution to babs presents a large increase reaching up to 39.1 ± 13.6% during winter nights (370 nm), suggesting residential wood burning (RWB) emissions as a dominant source for BrC. This is supported by strong correlations of the BrC absorption with OC, EC, the fragment ion m/z 60 derived from ACSM and PMF-analyzed organic fractions related to biomass burning (e.g. BBOA). In contrast, BrC absorption decreases significantly during daytime as well as in the warm period, reaching to a minimum during the early-afternoon hours in all seasons due to photo-chemical degradation. Estimated secondary BrC absorption is practically evident only during winter night-time, implying the fast oxidation of BrC species from RWB emissions. Changes in mixing-layer height do not significantly affect the BrC absorption in winter, while they play a major role in summer.

Effectively controlling hazardous airborne elements: Insights from continuous hourly observations during the seasons with the most unfavorable meteorological conditions after the implementation of the APPCAP

Concentrations of PM2.5 and PM2.5-associated elements were observed hourly using an X-ray fluorescence-based online elemental analyzer at a chosen location within urban Beijing from November 28, 2016, to May 30, 2017, when nearly the lowest atmospheric environmental capacity was recorded after enforcing the Air Pollution Prevention and Control Air Plan (APPCAP). Throughout the study period, the PM2.5 concentrations were an average of 91.2 μg/m3, with 68 days exceeding the second tier of the Chinese ambient air quality standard (75 μg/m3). The PM2.5-associated hourly hazardous airborne element (HAE) concentrations ranged between 56 ng/m3 and 4374 ng/m3, accounting for an average of 0.2 ± 0.1 % of PM2.5, which were lower than or comparable with those reported in previous studies. Different from the traditional filter sampling offline analysis, dynamic variations and evolution of particulate HAEs were illustrated based on hourly observations, which showed that the concentrations of most HAEs declined with increasing mixed layer height (MLH) as expected, while slight increases in the Cr and Pb concentrations were observed when the MLH increased from 250 m to 500 m. Compared with the values in spring, As, Cr, Hg, Mn, Ni, Pb and Se increased by 135.0 %, 67.2 %, 110.1 %, 36.4 %, 32.4 %, 185.6 % and 63.9 % in winter, respectively. Based on hourly elemental data, the more robust source analysis showed that industrial emissions contributed substantially to Cr, Hg, Ni and Se (58.5 %, 42.7 %, 65.0 % and 62.0 %, respectively), vehicular sources primarily accounted for Mn (41.1 %) and almost all sources except for dust contributed equally to the Pb loading. A nonparametric wind regression analysis applied to 1-h HAE concentrations pinpointed distinct hot spots (high concentrations) for all HAEs except Cd in the northeast wind sector at wind speeds of approximately 0−6 km/h. Based on a potential source contribution function analysis, the areas in western China with intense coal consumption strongly contributed to the loading of As in Beijing. Cr, Hg, Ni, Pb and Se showed source areas that were similar to but larger than that of As; additionally, these elements exhibited moderate and strong hotspots in Shanxi Province with strong coal consumption and industrial production. Ni clearly originated from the coastal areas where the effect of shipping activities was intense.

Air quality in Mexico city during the fuel shortage of January 2019

The closure of pipelines to tackle fuel-theft in central Mexico caused an unexpected fuel shortage that disrupted transport systems in Mexico City in January of 2019. Fuel sales in the Metropolitan Area and CO emissions from reanalysis showed a significant decrease during the fuel shortage of 7% and 6%, respectively. This study analyses the air quality and meteorological conditions during this period to evaluate whether these measures indirectly affected air quality in Mexico City. During the shortage, mean-ambient concentrations of nitric oxide (NO), nitrogen dioxide (NO2) and carbon monoxide (CO) were significantly lower than normal whereas levels of particulate matter (PM) were only modestly lower than usual. Daily-mean NO and CO had record-low anomalies of −10 ppb and −0.5 ppm from typical days, respectively. In contrast, ozone mean-levels were not significantly different than average. The percentage of days with PM mean concentrations above the World Health Organisation guidelines (5 and 19% for particles smaller than 2.5 and 10 μm, respectively) and the percentage of ozone 8-h rolling means above Mexican law (0.5%) were record lows. Meteorological factors, such as wind speed or the mixed-layer height were not significantly different than average. The anomalously low pollution levels were accentuated when each day was compared to days of similar flow patterns. This episode of better than usual air quality showcases how strategies addressing transport emissions could control air quality in Mexico City and highlights that improving ozone mean levels require comprehensive strategies that reduce emissions from all sectors.

Long-term variability, source apportionment and spectral properties of black carbon at an urban background site in Athens, Greece

This study aims to delineate the characteristics of Black Carbon (BC) in the atmosphere over Athens, Greece, using 4-year (May 2015–April 2019) Aethalometer (AE-33) measurements. The average BC concentration is 1.9 ± 2.5 μg m−3 (ranging from 0.1 to 32.7 μg m−3; hourly values), with a well-defined seasonality from 1.3 ± 1.1 μg m−3 in summer to 3.0 ± 4.0 μg m−3 in winter. Pronounced morning and evening/night peaks are found in the BC concentrations in winter, while during the rest of the seasons, this diurnal cycle appears to flatten out, with the exception of the morning traffic peak. On an annual basis, the biomass-burning fraction (BB%) of BC accounts for 22 ± 12%, while the fossil-fuel combustion (BCff) component (traffic emissions and domestic heating) dominates during summer (83%) and in the morning hours. BCwb exhibits higher contribution in winter (32%), especially during the night hours (39%). BC levels are effectively reduced by precipitation, while they significantly build-up for wind speeds <3 m s−1 and mixing-layer height (MLH) < 500 m. Normalizing the BC diurnal course by the MLH variations on a seasonal basis reveals that the residential wood-burning emissions are mostly responsible for the large BC increase during winter nights, whereas the low BC levels during daytime in the warm season are mainly attributed to dilution into a deeper MLH. BCwb is highly correlated with other BB tracers during winter nights (e.g. levoglucosan, non-sea-salt-K+, m/z 60 fragment), as well as with the fine fraction (PM2.5) OC and EC. The Delta-C, which represents the spectral dependence of BC as the absorption difference between 370 and 880 nm, is analyzed for the first time in Athens. It exhibits a pronounced seasonality with maximum values in winter night-time, and it appears as a valid qualitative marker for wood combustion.

Impact of mixing layer height on air quality in winter

Air quality in Delhi is largely dependent on concentration of aerosol particulate matter with aerodynamic diameter less than 2.5 μm (PM2.5). Diurnal variation of PM2.5 is mainly determined by rates of emission, deposition, chemical reactions and turbulent mixing caused by vertical wind shear and buoyancy. Continuous observations of PM2.5, NOx and O3 along with mixing layer height (MLH) by ceilometer (Vaisala CL51) in Delhi (Lodi road) during December 2017, January and February 2018 are analyzed. Comparison of MLH in winter (December) obtained from ceilometer and radiosonde showed good agreement in 66% of the cases for stable conditions and 36% of the cases for convective conditions. Diurnal variation revealed relatively low PM2.5 and NOx during convective period coinciding with high MLH while O3 registered higher concentration proportional to solar radiation. PM2.5 mass density was found to be inversely correlated to MLH during convective period. The mass density decreased by 14, 13 and 7 μgm−3 in December, January and February respectively for every 100 m increase of MLH. Variation of PM2.5 normalized by MLH qualitatively illustrated the influence of MLH on air quality in terms of dilution and accumulation during convective and statically stable conditions respectively. NOx and O3 had better correlations with MLH as compared to that of PM2.5. Air quality index in Delhi during winter with very low wind speed is mainly determined by MLH except during morning transition from stable to unstable condition.

Vertical Distribution and Transport of PM2.5 During Heavy Pollution Events in the Jing-Jin-Ji Region

Based on vehicle-borne tethered balloon measurements, the vertical distribution of particulate matter (PM) concentrations were observed in Gaocun in the Wuqing District of Tianjin from December 17 to 19, 2016, during a period of heavy pollution. Using observational data, the transport flux of PM2.5 in the Jing-Jin-Ji region was calculated. The results showed that the mixed layer was low at only 200 m during the heavy pollution period. The vertical distribution of PM2.5 concentrations was closely associated with the heights of mixed layer whereby, below the mixed layer, PM2.5 concentrations were higher. Vertical variation was insignificant, forming a district pollution layer. Above the mixed layer, PM2.5 concentrations rapidly decreased and stabilized at low levels. During the observation period, higher concentrations of PM were found with particle sizes of less than 1.0 μm, and lower concentrations were observed for particle sizes larger than 2.2 μm. The size profiles of PM tallied with relative humidity and the height of the mixed layer. The size distribution was wider during periods of high humidity and with a lower mixed layer height. The greatest PM2.5 transport flux was from the southwest, accounting for 63.3% of the total flux; the highest fluxes occurred at the heights of 46-156 m and 156-296 m. The dominant transport direction was southwest below 300 m, while the dominant transport direction was dispersed over 300 m.

Multivariate statistical air mass classification for the high-alpine observatory at the Zugspitze Mountain, Germany

Abstract. To assist atmospheric monitoring at high-alpine sites, a statistical approach for distinguishing between the dominant air masses was developed. This approach was based on a principal component analysis using five gas-phase and two meteorological variables. The analysis focused on the Schneefernerhaus site at Zugspitze Mountain, Germany. The investigated year was divided into 2-month periods, for which the analysis was repeated. Using the 33.3 % and 66.6 % percentiles of the first two principal components, nine air mass regimes were defined. These regimes were interpreted with respect to vertical transport and assigned to the BL (recent contact with the boundary layer), UFT/SIN (undisturbed free troposphere or stratospheric intrusion), and HYBRID (influences of both the boundary layer and the free troposphere or ambiguous) air mass classes. The input data were available for 78 % of the investigated year. BL accounted for 31 % of the cases with similar frequencies in all seasons. UFT/SIN comprised 14 % of the cases but was not found from April to July. HYBRID (55 %) mostly exhibited intermediate characteristics, whereby 17 % of the HYBRID class suggested an influence from the marine boundary layer or the lower free troposphere. The statistical approach was compared to a mechanistic approach using the ceilometer-based mixing layer height from a nearby valley site and a detection scheme for thermally induced mountain winds. Due to data gaps, only 25 % of the cases could be classified using the mechanistic approach. Both approaches agreed well, except in the rare cases of thermally induced uplift. The statistical approach is a promising step towards a real-time classification of air masses. Future work is necessary to assess the uncertainty arising from the standardization of real-time data.

Mixing layer height and slope wind oscillation: Factors that control ambient air SO2 in a tropical mountain city

Distinct times of sulfur dioxide concentration (SO2) were observed in the main square of a tropical Andean city, revealing strong meteorological control of SO2. Concentrations were measured by UV fluorescence at 5-minute intervals, and compared to local meteorological forcing. A consistent morning peak of SO2 (4.32 μg∙m⁻³ at 7:40 AM) was concurrent with peak traffic, and occurred 10 minutes into an 80-minute period of calm (wind velocities ˂ 0.3 m s⁻1). Instead of accumulating, SO2 decreased 54%, due an expanding mixing layer. Peak evening SO2 (5.2 μg∙m⁻³ at 8:15 PM) was observed 2:15 hours after flow reversal, and consistent with travel-times of an air parcel descending from industrial facilities. The consistent anthropogenic emissions formed a pattern of daily SO2 concentration that aided in identifying more random volcanic SO2. Manizales (pop. 400000) is located on the western slope of the Cordillera Central in proximity to the Nevado del Ruiz volcano. The complex trajectory necessary for volcanic SO2 to arrive in the main square was simulated for the highest observed concentration (114 μg•m⁻³), using Hysplit and Aura-OMI information. This type of analysis can be applied to urban planning - from locating industrial zones to managing transportation - particularly in tropical montane cities.

Characteristics of Heavy Particulate Matter Pollution Events Over Hong Kong and Their Relationships With Vertical Wind Profiles Using High‐Time‐Resolution Doppler Lidar Measurements

AbstractPrevious studies have reported boundary layer features related to air pollution. However, few studies have comprehensively evaluated the characteristics and mechanisms of vertical wind in the formation and evolution of heavy particulate matter pollution episodes (EP) in Hong Kong. In this study, we analyzed the vertical characteristics of heavy particulate matter (PM) pollutions over Hong Kong and their relationships with vertical wind profiles using high‐time‐resolution Doppler lidar measurements and hourly meteorological and air quality observations. We identified nine EPs and show that the events were closely coupled to various vertical wind profiles in the planetary boundary layer (PBL). Our analysis suggests that strong vertical wind speed with wind shear at certain heights in the PBL had a positive correlation with surface PM during most superregional transboundary EPs. The maximum transport height extends from the surface to about 2.0 km or even higher; these transport heights differed among superregional and regional transboundary EPs. At peak surface pollution concentrations during the nine EPs, the surface PM10 had a significant negative correlation with PBL heights/mixing layer heights, while the averaged wind shear in the PBL was significantly positively correlated. These EPs with different mixing layer heights were mainly driven by different vertical wind shear conditions under various weather systems related to surface high pressure, cold fronts, dust storms, and typhoons. This work provides scientific evidence that surface PM pollutions were closely related to the characteristics of vertical profiles during the transboundary air pollutions.

An Overview of Low‐Level Jet Winds and Corresponding Mixed Layer Depths During PECAN

AbstractThirty southerly low‐level jet (LLJ) events were observed during the Plains Elevated Convection at Night (PECAN) field campaign in the Great Plains region of the United States during summer 2015. Here we present Doppler lidar wind data from three PECAN instrumentation sites to explore characteristics of LLJs and the boundary layer as well as some of the heterogeneities possible within the wind field of a LLJ. Southerly LLJs were observed on 66% of nights at the southwestern site (Greensburg, KS) but only 56% and 53% of nights at the eastern and northern sites, respectively (Hesston and Ellis, KS). The northernmost site had a relative abundance of weaker jets or nonjet conditions due to fronts or convective systems that only affected part of the observation domain. Plotting mean wind fields of each LLJ type reveals that the strongest LLJs tend to develop under very similar conditions but begin to show variability in wind profile evolution after several hours. A robust mixed layer height retrieval algorithm is used to investigate the interplay between the jets and the turbulent convective boundary layer, showing that stronger LLJs are preceded by deeper afternoon mixed layers and often have a later decoupling of mixing between the upper convective mixed layer and the near‐surface layer. Only the strongest LLJs generated a shallow mixing layer overnight. Comparing jet strength and direction to pristine nocturnal convection initiation shows that the strongest southerly LLJs yielded the most pristine nocturnal convection initiation events per night, and the pristine nocturnal convection initiation occurred farther north.