#1EGU General Assembly 2020 online Factors influencing the boundary layer height and their relationship with air quality in the Sichuan Basin, China Bangjun Cao Plateau Atmosphere and Environment Key Laboratory of Sichuan Province, School of Atmospheric Sciences, Chengdu University of Information Technology 2020.4.20#21.1 The spatial distribution characteristics of areas with severe air pollution in China It is a common phenomenon around the world that the cities located in complex terrain are prone to form heavy air pollution Beijing Tianjin-Hebei Tibet Plateaus Sichuan B Pear The depth of this basin is more than 2500 m, and urban agglomerations are developing fast over there 1#3Three-dimensional topographic map of Sichuan Basin It is a common phenomenon around the world that the cities located in complex terrain are prone to form heavy air pollution Three-dimensional topographic map of Sichuan Basin 8000 7000 6000 5000 4000 3000 2000- 海拔高度 1000 ~2500m 0 100 101 102 103 104 105 经度 106 107 28 108 27 109 26 110 25 The depth of this basin is more than 2500 m, and urban agglomerations are developing fast over there#4Factors influencing the boundary layer height 1. the inversion temperature layer below the bottom of troposphere Pressure (hPa) Pressure (hPa) (a) 08:00 BST 12 December 500 600 700 800 900 1000 +............ -10 -5 0 500 + 600 700 800 900 5 10 Temperature (°C) (b) 08:00 BST 16 December 1000 -15 -10 -5 Your site here - OBS 15 Era-interim 0 5 10 15 Temperature The strong inversion layer in the lower troposphere over the Sichuan Basin leads to the accumulation of a large amount of water vapor below the inversion layer. The inversion at the height of the plateau over eastern China is generated by the advection of warm air from the plateau, which provides favorable thermodynamic conditions for mid-level clouds 1.daytime: reflect and absorb a large amount of downward shortwave radiation, reducing the downward shortwave radiation to the basin surface. Then, the surface heating to the atmosphere is very slow 2.nighttime: stop the upward longwave radiation from the surface, the near surface temperature decreases slowly, the diurnal temperature range is small#5Impact of inversion layer on the boundary layer height Inversion temperature like a reverse pot cover Sichuan Basin is like a basin Pollutant concentration increases quickly because of limited atmospheric diffusion space. 3#6Questions 1. How the impact of inversion layer on the boundary layer over the Sichuan Basin? 2. The traditional influencing factors on the boundary layer height is the surface sensible heat flux and wind shear. Are these factors would have effect on the boundary layer height over the Sichuan Basin? Your site here Company Logo#7Conclusion Factors affecting the boundary layer height (hmax) change in Sichuan Basin. • The inversion layer in troposphere is the main factor affecting hmax on cloudy days. The vertical wind shear is the main factors affecting max on sunny days. • The secondary circulation is much weaker on cloudy days than on sunny days. Pressure (hPa) Pressure (hPa) 34°N (a) 34°N 32°N- 32°N Chengdu Chengdu 0 30°N- 30°N 28°N 26°N Chongqing 28°N 26°N 96°E 98°E 100°E 102°E 104°E 106°E 108°E 110°E 96°E 98°E 100°E 102°E 104°E 105°E 108°E 110°E -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1. -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 (c) 2017-12-12 14 (d) 2017-12-13 14 550 550 600 600 650 700 750 800 850 Pressure (hPa) 650 700 750 800 850 925 925 1000 1000 102°E 104°E 106°E 108°E 102°E 104°E 106°E 108°E (e) 2017-12-16 14 (f) 2017-12-17 14 550 600 1000 888 28 550 600 650 700 750 800 850 925 Pressure (hPa) 650 700 750 800 850 925 1000 102°E 104°E 106°E 108°E 102°E 104°E 106°E 108°E Temperature (°C) -20-18-16-14-12-10 -8 -6 -4 -2 0 2 4 6 8 10 12 14 16 18 201 10 m s¹#8Pressure (hPa) (a) 08:00 BST 12 December 500 500 600 000 700 800 900 ***........ 0 Pressure (hPa) 600 700 800 900 (b) 08:00 BST 16 December -OBS Era-interim 1000 1000 -10 0 5 10 15 -15 -10 -5 0 5 10 15 Temperature (°C) Temperature (°C) Fig. 2. Temperature profiles from the ERA-Interim Reanalysis and the observational datasets on (a) cloudy and (b) sunny days.#934°N 32°N Sunny day Boundary layer height (a) m 34°N 32°N Boundary layer height Cloudy day (b) 30°N 30°N Chengdu Chengdu 28°N 26°N 96°E 98°E 100°E 102°E 104°E 106°E 108°E 110°E Boundary Layer Height (m) 28°N 26°N 96°E 98°E 100°E 102°E 104°E Boundary Layer Height (m) ΕΠ 106°E 108°E 110°E 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 hmax was higher on sunny days than on cloudy days Fig. 3. Distribution of the boundary layer height in the Sichuan Basin on (a) sunny and (b) cloudy days in winter 2017-2018. The oval outline is the Sichuan Basin and the red line is the border of the Tibetan Plateau.#10Pressure (hPa) Temperature K Specific humidity (b) kg kg**-1 U component of wind (c) 500 ms-1 500 500 700 850 1000 1213 1214 1215 Temperature (K) 262 266 270 274 278 282 286 290 294 Day Height (km) Pressure (hPa) 700 850 4 Height (km) Pressure (hPa) 700 850 1000 1000 1216 1213 1214 1215 1216 1213 1214 Specific humidity (kg kg-1) 1215 Wind speed (ms-1) 1216 0.001 0.004 0.007 0.01 0.013 0.016 Day -3 0 6 9 12 15 18 21 24 27 Day + Height (km) Transitional period from cloudy day to sunny day: temperature-the inversion temperature layer disappears relative humidity-the inversion layer in the specific humidity disappears horizon wind speed-the wind speed increases#111500 500 500 Height(m) 1000 и 12/13 12/14 12/15 ............. - BLH CF +4 (b) 120 110 CO 6 100 Clould fraction 90 90 lov AQI 80 50 70 2 60 60 50 wwwww - AQI ........ PM 2.5 PM 10 100 0 0 0 0 0 00 12/16 40 12/13 12/14 12/15 12/16 Date Date Transitional period from cloudy day to sunny day: the boundary layer height increases the cloud cover decreases the air quality becomes better 80 Particulate matter (μg m³)#12Factors influencing the boundary layer height Inversion layer height Inversion layer height PH, (Normalized) ION) 'Hייימוולמת) (a) 3 2 R²=0.52 C 1.5 1 0.5 0 2 1.5 0 1.5 2 (Normalized) 0.5 h 1 max (c) R²=0.52 1 0.5 0 0.5 h 1 1.5 2 (Normalized) max S.(Normalized) T, (Normalized) 0 3 2 (b) Strength of Inversion layer 1 2 3 h (Normalized) max (d) • Strength of Inversion layer During cloudy days, strong correlation between PH, and hmax with a correlation coefficient, The correlation between S, and hmax was lower 0 1 2 3 4 h (Normalized) max than that of PH; Fig. 6. Relation between the height of the base of the inversion layer and (a) PH; and (c) H₁, (b) the inversion temperature (S,) and (d) the thickness of the inversion layer (T;) and the boundary layer height on cloudy days.#13Impact of inversion layer on the boundary layer height Inversion temperature like a reverse pot cover Sichuan Basin is like a basin Pollutant concentration increases quickly because of limited atmospheric diffusion space. 3#1434°N Sunny day (a) 34°N Cloudy day (b) 32°N 32°N Chengdu Chengdu 30°N 30°N 28°N 26°N 28°N Chongqing 96°E 98°E 100°E 102°E 104°E 106°E 108°E 110°E -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 Correlation Coefficient 26°N Chongqing good correlation between h max and the sensible heat flux in the central Sichuan Basin on sunny 96°E 98°E 100°E 102°E 104°E 106°E 108°E 110°E days than that -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 Correlation Coefficient on the cloudy days Fig. 7. Significance test of the correlation between the sensible heat flux and hmax on (a) sunny and (b) cloudy days in Sichuan Province. The leftmost red dot is Chengdu and the rightmost red dot is Chongqing. The oval shape reflects the outline of the Sichuan Basin.#15Chengd u Hsmax (Normalized) 1.5 2 Sunny day Hsmax (Normalized) 2 1.5 Cloudy day 0.5 R²=0.42 0.5 O R²=0.12 000 О 0 0 0 0.5 1 1.5 2 0.5 1 1.5 2 h (Normalized) 'max' max' (c) (d) 2 2 1.5 Hsmax (Normalized) 1.5 h (Normalized) good correlation between h max and the sensible heat flux in the central Sichuan Basin on sunny days than that Chong qing Hsmax (Normalized) 0.5 ဝထ R²=0.51 0.5 R²=0.21 0 0.5 1 1.5 2 0 0.5 1 1.5 2 max h (Normalized) h (Normalized) max on the cloudy days Fig. 8. Correlation between the sensible heat flux and hmax at Chengdu on (a) clear and (b) cloudy days and at Chongqing on (c) clear and (d) cloudy days.#1634°N 32°N 30°N 28°N 26°N Sunny day (a) 34°N 32°N Chengdu 30°N Chongqing 28°N 96°E 98°E 100°E 102°E 104°E 106°E 108°E 110°E -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 26°N Cloudy day (b) Chengdu Chongging 96°E 98°E 100°E 102°E 104°E 106°E 108°E 110°E -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 The correlation between hmax and the turbulent surface stress in the central region of the Sichuan Basin was excellent on Fig. 9. Significance test of correlation between the wind shear and the boundary lay sunny days than cloudy and (b) sunny days in Sichuan Province. The oval shape reflects the outline of Basin. that on cloudy days#17Chengdu Chongqing Wsh (Normalized) Wsh (Normalized) 2 1.5 Sunny day 0.5 2 1.5 0.5 0 1 (Normalized) 0 0 0.5 h max (c) 0 0.5 1 h (Normalized) max R²=0.73 Wsh (Normalized) 1.5 0.5 2 Cloudy day 0 1.5 2 0 0.5 R²=0.72 1.5 Wsh (Normalized) 1.5 0.5 R²=0.09 0.5 1 h (Normalized) max (d) R²=0.11 1.5 водо 2 1 1.5 2 h (Normalized) max Fig. 10. Relationship between wind shear and the boundary layer height at Chengd (b) cloudy days and at Chongqing Station on (c) clear and (d) cloudy days. The correlation between hmax and the turbulent surface stress in the central region of the Sichuan Basin was excellent on sunny days than that on cloudy days#18Cloudy day Sunny day Pressure (hPa) Pressure (hPa) Inversion layer height The secondary circulation in the boundary layer 650 700 (a) 2017-12-12 14 (b) 2017 10 12 14 550 600 650 700 750 800 850 925 1000 925 1000 102°E 104°E 106°E 108°E 102°E 104°E 106°E 108°E (c) 2017-12-16 14 Boundary layer height Pressure (hPa) (d) 2017-12-17 14 550 550 600 600 650 650 700 700 750 750 800 800 850 850 925 925 1000 1000 102°E 104°E 106°E 108°E 102°E 104°E 106°E 177777 Temperature (°C) -20-18-16-14 -12 -10 -8 -6 -4 -20 2 4 6 8 10 12 14 16 18 20 108°E was stronger on sunny days than on cloudy days. This stronger secondary circulation increased the wind shear and turbulent mixing and provided the energy required to 10ms increase hmax Fig. 11. West-east vertical cross-sections of temperature (shading; units: °C) and wind vectors (synthesized by u and w) through the Sichuan Basin (30.75° N) on sunny days at (a) 14:00 BST on December 12, 2019, (b) 08:00 BST on December 13, 2017 and on cloudy days at (c) 14:00 BST on December 16, 2017 and (d) 14:00 BST on December 17, 2017. The vertical velocity is multiplied by 100 when plotting the wind vectors. The most polluted area is marked by red dots. The gray shading represents the terrain. The solid line represents the base of the inversion layer and the red dotted line represents max. This area is not clearly visible.#19Thank you!