Wintertime vertical distribution of black carbon and single scattering albedo in a semi-arid region derived from tethered balloon observations

The vertical distribution of atmospheric aerosols plays an essential role in aerosol-radiation and aerosol-cloud interactions. Because of strong light absorption, the radiative effects of black carbon (BC) are highly sensitive to its vertical distribution; the lack of high-resolution observations is the reason for their poor quantification. We used a tethered balloon platform to acquire high-resolution vertical profiles of BC, particle number concentration, and meteorological parameters in the semi-arid region of Northwest China in December 2018. A total of 112 BC profiles were classified into four vertical distribution categories, which were determined by local emissions, regional transport, vertical mixing due to the ABL evolution, and topography. BC profiles with peaks near or above the atmospheric boundary layer (ABL) accounted for 57% of the profiles. Vertical single scattering albedo (SSA) profiles were subsequently calculated using the profiles of BC and particle size distribution. The vertical SSA distribution is generally modulated by BC profiles. The diurnal variations of the BC and SSA profiles were summarized using a boundary-layer normalization method. In the ABL, BC decreased and SSA increased with increasing height at 02:00, 08:00, and 20:00, while both BC and SSA exhibited a uniform distribution at 14:00. The SSA decreased above the ABL at 14:00, which might have had a profound impact on ABL development. These results provide a better understanding of the vertical BC and SSA distributions, which can also be used to reduce uncertainties in estimating the BC radiative effects.

Aggravated ozone pollution in the strong free convection boundary layer

Clarifying the relationship between meteorological factors and ozone can provide scientific support for ozone pollution prediction, but the effects of boundary layer meteorology, especially boundary layer height and turbulence, on ozone pollution are rarely studied. Here, ozone and its related meteorological factors were observed in summer in Shijiazhuang, a city with the most serious ozone pollution on the North China Plain. The forced and free convection boundary layers were classified using ground remote observations. After eliminating the forced convection condition, strong free convection conditions, exhibiting a high boundary layer height, high wind speed, strong turbulence and large-scale free convection velocity, were found to be beneficial for the aggravation of ozone pollution. Combined with the ozone profile detected by a tethered balloon, the ozone chemical budget was calculated using the differences in the column ozone concentrations between the morning and afternoon, and the results confirmed the impact of free convection intensity on ozone pollution. The change in ozone sensitivity from VOCs sensitivity to NOx sensitivity driven by strong free convection was the main reason for the deterioration of ozone pollution. This study clarified the impact of boundary layer meteorology on ozone and its sensitivity and has important practical significance for ozone pollution prevention and early warning.

A lightweight low-cost and multipollutant sensor package for aerial observations of air pollutants in atmospheric boundary layer

A lightweight low-cost multipollutant sensor package is particularly portable to aerial measurements and field campaign due to its light weight (2.0 kg), compact size (L × W × H, 22 × 15 × 10 cm), and low energy-consumption (20 Wa). The sensor system consists of electrochemical sensors measuring O₃, NO₂, NO, SO₂, CO, an optical counting (OPC) particulate matter (PM) sensor for PM_1.0, PM_2.5, and PM₁₀, a miniature photoionization detector (PID) for total volatile organic compounds (TVOCs), and metrological sensors for air temperature, relative humidity (RH) and air pressure. All sensor signals were collected and transferred by a data acquirement (DAQ) logger. The sensor data were saved in a microcomputer and transmitted wireless by a GSM/GPS module. All sensors and the accessories were integrated and installed in a thermal insulation foam package, of which temperature was stable at 25 °C to avoid the temperature effect. A silicone desiccant tube was connected to the inlet of air sample to minimize the RH influence. The sensor performances were compared with on-ground reference instruments for a 21-day field campaign and commercial portable instruments from Thermal Scientific and Vaisala in aerial observations. All gas sensors and PM sensor showed good correlations with the reference instruments with R² varying from 0.81 to 0.93 and slope from 0.89 to 1.35. The O₃ sensor performed best with R² = 0.93 and slope = 1.02. In aerial measurements PM and O₃ sensors obtained similar vertical profiles of PM and O₃ with those obtained by commercial Thermal PTR PM monitor and Vaisala O₃ sounding sensor, respectively. The sensor package was successfully deployed to observe the vertical profiles of air pollutants on a tethered balloon and to exactly locate exhaust sources in an industrial park with an unmanned aerial vehicle (UAV). Our sensor package was substantiated to be a reliable and accurate device for aerial measurements of air pollutants in atmospheric boundary layer (ABL).

Vertical distribution of volatile organic compounds conducted by tethered balloon in the Beijing-Tianjin-Hebei region of China

Volatile organic compounds (VOCs) as precursors of ozone and secondary organic aerosols can cause adverse effects on the environment and human health. However, knowledge of the VOC vertical profile in the lower troposphere of major Chinese cities is poorly understood. In this study, tethered balloon flights were conducted over the juncture of Beijing-Tianjin-Hebei in China during the winter of 2016. Thirty-six vertical air samples were collected on selected heavy and light pollution days at altitudes of 50-1000 meters above ground level. On average, the concentration of total VOCs (TVOCs) at 50-100 m was 4.9 times higher than at 900-1000 m (46.9 ppbV vs. 8.0 ppbV). TVOC concentrations changed rapidly from altitudes of 50-100 to 401-500 m, with an average decrease of 72%. With further altitude increase, the TVOC concentration gradually decreased. The xylene/benzene ratios of 34/36 air samples were lower than 1.1, and the benzene/toluene ratios of 34/36 samples were higher than 0.4, indicating the occurrence of aged air mass during the sampling period. Alkenes contributed most in terms of both OH loss rate (39%-71%) and ozone formation potential (40%-72%), followed by aromatics (6%-38%). Finally, the main factors affecting the vertical distributions of VOCs were local source emission and negative dispersion conditions on polluted days. These data could advance our scientific understanding of VOC vertical distribution.

Sources and vertical distribution of PM2.5 over Shanghai during the winter of 2017

Shanghai, a metropolitan city in China, has suffered from severe air pollution, especially PM_2.5, in the last few years. Up to now the contribution of local emission and regional transport to the formation of haze in Shanghai remains unclear. With an aim to characterize the mechanism of haze formation in Shanghai, the present paper attempted to provide an overview of a tethered balloon-based field campaign. According to the backward trajectories, the air mass traveling slowly from Jiangsu province accounted for the highest PM_2.5 concentration (66 ± 20 μg/m³). Seventy vertical profiles of PM_2.5, NO, NO₂, SO₂ and O₃ within 1000 m were obtained, through which a comparison study on the characteristics of the vertical distributions of air pollutants on clean days and haze days was conducted. When altitude increased, clearly decreasing pattern of PM_2.5, NO, and NO₂ was observed during the field campaign. Due to the low atmospheric boundary layer, the diffusion of air pollutants was suppressed, which favored the formation of haze. The results of the generalized additive model revealed NO₂ could the most significant factor influencing the vertical distribution of PM_2.5 in both clean and haze days. This study provides new insight into the sources and vertical distribution of PM_2.5, which could offer references for air pollution modeling.

Vertical distributions of black carbon aerosols over rural areas of the Yangtze River Delta in winter

Based on a field campaign in Shouxian, a rural site on the Yangtze River Delta, China, from December 14, 2016 to January 4, 2017, the vertical profiles of black carbon (BC) and planetary boundary layer (PBL) structures were studied. In total, 58 vertical profiles were obtained, including of the PM_2.5, BC mass concentration (m_BC) and relevant meteorological parameters. Four profile types were categorized: I: uniform vertical distributions (38%), II: higher values at lower altitudes (29%), III: bimodal distributions with high values near the ground and at higher altitudes (17%), and IV: unimodal distributions with high values at higher altitudes (11%). A further analysis confirmed that all types were mainly influenced by the PBL diurnal evolution and local emissions, while types III and IV were strongly associated with the temperature inversions at low altitudes. The diurnal variations of the BC vertical profiles mainly followed the evolution of the PBL. In the early morning, the average m_BC within the PBL (M_{BL, BC}) increased significantly, reaching the highest level in the diurnal cycles, i.e., approximately 13.0 μg m^-3. The pollutants were confined to a thin layer <0.2 km above the ground, which contributed to the smoke produced by local residential biomass burning. Around noon, the accumulated BC in the layer was diluted as a result of the development of the PBL. The height of the PBL (H_PBL) reached its maximum in the afternoon, with an average of 0.65 km, while M_BL, _BC dropped to its minimum, with an average of 7.8 μg m^-3. As evening approached, the BC produced by local residential biomass burning gradually accumulated near the ground and linearly declined along the standardized height (H_S) within the nocturnal boundary layer (NBL). There were large differences in the BC concentration within and above the PBL both in the daytime and at night.

Impact of fugitive sources and meteorological parameters on vertical distribution of particulate matter over the industrial agglomeration

The aim of the study was to characterize vertical distribution of particulate matter, in an area well known by highest air pollution levels in Europe. A balloon filled with helium with measuring instrumentation was used for vertical observation of air pollution over the fugitive sources in Moravian-Silesian metropolitan area during spring and summer. Synchronously, selected meteorological parameters were recorded together with particulate matter for exploration its relationship with particulate matter. Concentrations of particulate matter in the vertical profile were significantly higher in the spring than in the summer. Significant effect of fugitive sources was observed up to the altitude ∼255 m (∼45 m above ground) in both seasons. The presence of inversion layer was observed at the altitude ∼350 m (120-135 m above ground) at locations with major source traffic load. Both particulate matter concentrations and number of particles for the selected particle sizes decreased with increasing height. Strong correlation of particulate matter with meteorological parameters was not observed. The study represents the first attempt to assess the vertical profile over the fugitive emission sources - old environmental burdens in industrial region.

Tethered balloon-born and ground-based measurements of black carbon and particulate profiles within the lower troposphere during the foggy period in Delhi, India

The ground and vertical profiles of particulate matter (PM) were mapped as part of a pilot study using a Tethered balloon within the lower troposphere (1000m) during the foggy episodes in the winter season of 2015-16 in New Delhi, India. Measurements of black carbon (BC) aerosol and PM <2.5 and 10μm (PM_2.5 & PM₁₀ respectively) concentrations and their associated particulate optical properties along with meteorological parameters were made. The mean concentrations of PM_2.5, PM₁₀, BC_370nm, and BC_880nm were observed to be 146.8±42.1, 245.4±65.4, 30.3±12.2, and 24.1±10.3μgm^-3, respectively. The mean value of PM_2.5 was ~12 times higher than the annual US-EPA air quality standard. The fraction of BC in PM_2.5 that contributed to absorption in the shorter visible wavelengths (BC_370nm) was ~21%. Compared to clear days, the ground level mass concentrations of PM_2.5 and BC_370nm particles were substantially increased (59% and 24%, respectively) during the foggy episode. The aerosol light extinction coefficient (σ_ext) value was much higher (mean: 610Mm^-1) during the lower visibility (foggy) condition. Higher concentrations of PM_2.5 (89μgm^-3) and longer visible wavelength absorbing BC_880nm (25.7μgm^-3) particles were observed up to 200m. The BC_880nm and PM_2.5 aerosol concentrations near boundary layer (1km) were significantly higher (~1.9 and 12μgm^-3), respectively. The BC (i.e BC_tot) aerosol direct radiative forcing (DRF) values were estimated at the top of the atmosphere (TOA), surface (SFC), and atmosphere (ATM) and its resultant forcing were - 75.5Wm^-2 at SFC indicating the cooling effect at the surface. A positive value (20.9Wm^-2) of BC aerosol DRF at TOA indicated the warming effect at the top of the atmosphere over the study region. The net DRF value due to BC aerosol was positive (96.4Wm^-2) indicating a net warming effect in the atmosphere. The contribution of fossil and biomass fuels to the observed BC aerosol DRF values was ~78% and ~22%, respectively. The higher mean atmospheric heating rate (2.71Kday^-1) by BC aerosol in the winter season would probably strengthen the temperature inversion leading to poor dispersion and affecting the formation of clouds. Serious detrimental impacts on regional climate due to the high concentrations of BC and PM (especially PM_2.5) aerosol are likely based on this study and suggest the need for immediate, stringent measures to improve the regional air quality in the northern India.

Origin of non-spherical particles in the boundary layer over Beijing, China: based on balloon-borne observations

Vertical structures of aerosols from the ground to about 1,000 m altitude in Beijing were measured with a balloon-borne optical particle counter. The results showed that, in hazy days, there were inversions at approximately 500-600 m, below which the particulate matters were well mixed vertically, while the concentration of particles decreased sharply above the mixing layer. Electron microscopic observation of the particles collected with the balloon-borne impactor indicates that the composition of particles is different according to weather conditions in the boundary mixing layer of Beijing city and suggests that dust particles are always dominant in coarse-mode particles. Interestingly, sea-salt particles are frequently identified, suggesting the importance of marine air inflow to the Beijing area even in summer. The Ca-rich spherical particles are also frequently identified, suggesting chemical modification of dust particle by NOx or emission of CaO and others from local emission. Additionally, those types of particles showed higher concentration above the mixing layer under the relatively calm weather condition of summer, suggesting the importance of local-scale convection found in summer which rapidly transported anthropogenic particles above the mixing layer. Lidar extinction profiles qualitatively have good consistency with the balloon-borne measurements. Attenuation effects of laser pulse intensity are frequently observed due to high concentration of particulate matter in the Beijing atmosphere, and therefore quantitative agreement of lidar return and aerosol concentration can be hardly observed during dusty condition. Comparing the depolarization ratio obtained from the lidar measurements with the balloon-borne measurements, the contribution of the dry sea-salt particles, in addition to the dust particles, is suggested as an important factor causing depolarization ratio in the Beijing atmosphere.