Relationships between Synoptic- and Meso-scale scale Conditions and NO x Concentrations in Tel-Aviv

Transcription

1 Relationships between Synoptic- and Meso-scale scale Conditions and NO x Concentrations in Tel-Aviv Tania Uman 1 Hadas Saaroni 1 Baruch Ziv 2 1 Department of Geography, Tel Aviv University, Israel 2 The Open University of Israel

2 OUTLINE Background: the synoptic classification Data base Pollution events Pollution potential of the synoptic types The coastal circulation and its interaction with the synoptic conditions

3 THE SYNOPTIC CLASSIFICATION Alpert et al. (24) Int. J. Climatol., 24, types of EM synoptic systems that belong to 5 synoptic groups were defined The experts subjectively classified the synoptic system for each day (1985+DJF1991/2) to one of 19 types The synoptic type for each day ( ) was determined by computerized process that defined the closest type to one of the 19 types

4 The 5 synoptic groups Highs Persian Trough Red Sea Trough Over Israel Strong Central axis Sharav Lows West of Israel Deep to North Lows

5 Study area and Data Base

6 Data base: 1. NO x data: 3 min average concentrations. Data was taken from 7 monitoring stations operated by the Ministry of the Environment in the Tel-Aviv metropolitan area. 2. Synoptic data base: Synoptic classification by Alpert et al.. (24) based on NCEP/NCAR reanalysis data from 12 UTC Study period:

7 יד אבנר רמ ז עירוני ד' תחבורתיות (Traffic) כלליות (General) f Study גבעתיים area ע מיא ל טיפת ח ל ב חו לון

8 Pollution events

9 The Israeli standard for NO x is: 5 ppb (for 3 min average) exceeding day - a day in which at least 1 station recorded, at least once, NO x concentration above the standard 19% of the days were exceeding days But only 2% of the individual observations

10 Exceeding observations in the individual stations (%) Average עמיאל עירוני ד' טיפת- חלב רמז חולון יד-אבנר גבעתיים General Traffic Traffic monitoring stations show highest pollution Large differences among individual stations

11 Inter-annual variation of exceeding days (%) 3 25 y = x An improving trend can be noted. Is it the outcome of improved regulations, or a change in the synoptic conditions?

12 Yearly course of exceeding days (%) DEC NOV OCT SEP AUG JUL JUN MAY APR MAR FEB JAN The winter months (Nov-Feb) impart the majority of exceeding days. The summer is clean.

13 Weekly course of exceeding days (%) Weekend Sat Fri Thu Wed Tue Mon Sun Day of the week The Israeli weekend (Fri-Sat) has 5% reduction in exceeding occurrence

14 Pollution potential of the synoptic types

15 Occurrence according the 5 synoptic groups Exceeding days (477 days) Lows 1% Sharav Lows 1% Study period (2557 days) Highs 35% RST 51% Lows 16% Sharav Lows 1% RST 25% Persian trough 3% Highs 28% Persian trough 3%

16 Pollution potential: % exceeding days of the total no. of days belonging to each group RST Total No. of exceeding days belonging to each synoptic group 16 Persian trough Highs Lows Sharav lows 6 Over third of the RST days were exceeding days Over half of the exceeding days belong to RST

17 % Pollution potential for the 6 types with the highest potential extensive exceeding day - day in which at least 4 of 7 stations recorded concentration above the standard (~1 days a year) 14 8 RST Western axis 57 Highs to the east Total No. of extensive exceeding days belonging Total to each No. of synoptic exceeding days belonging type to each synoptic type 125 RST Central axis Highs to the north Sharav low over Israel deep low to the east Four of them, including that with the highest potential, are cyclonic types

18 Main synoptic results The synoptic group with the highest pollution potential is cyclonic - Red Sea Trough The highest pollution potential belongs to types associated with easterly (offshore) flow WHY?

19 The coastal circulation and its interaction with the synoptic conditions

20 Relationships between Synoptic- and Meso-scale scale Conditions Hot & Dry (synoptic) Cool & wet (meso-scale) We suggest that the high pollution results from the combination of high stability and light winds associated with the sea breeze underneath the warm easterly flow

21 Relationship between inter-annual variation of exceeding days and frequency of synoptic groups responsible for high pollution potential Exceeding RST+HIGHS LOWS Positive correlation between Rst+Highs and N of exceeding days (R=.69) Negative correlation between Lows and N of exceeding days (R=-.56)

22 % of exceeding days and extensive exceeding days ( ) under more strict standards 59% 6% 33% 23% 19% 1% 3% 5% 4% 3% 2% 1% % תקן 5 חל"ב (הנוכחי) תקן 375 חל"ב ) 3/4 מהתקן הנוכחי) תקן 25 חל"ב ) 1/2 מהתקן הנוכחי)

23 MAIN FINDINGS AND CONCLUSIONS NO x concentrations exceed the standard ~2% of the days especially during the winter The Red Sea Trough is the synoptic system with the highest pollution potential and the second is a high pressure system The synoptic type with the highest pollution potential is the Red Sea trough with axis to the west The synoptic conditions which are favorable for high NO x concentration is associated with easterly offshore flow The apparent decrease in exceeding days from 1998 to 24 reflects actually the decrease in synoptic types having high pollution potential

24

25 נס פח ים

26 19 Sharav low over Israel 18 Sharav low low to west 17 shallow low to east 16 cold low to the west 15 shallow low to the north 14 deep low to the north 13 shallow low to south 12 deep low to the south 11 deep low to the east 1 Highs over Israel 9 Highs to the north 8 Highs to the west 7 Highs to the east 6 strong persian trough 5 medium persian trough 4 weak persian trough RST3 Central axis RST2 Western axis RST1 Eastern axis אחוז ההו פעה של ה מצב בי מ י חריגה מ ת וך הכלל %

27 Pollution potential: % extensive exceeding days of the total no. of exceeding days Total No. of extensive exceeding days belonging to each synoptic group RST Persian trough Highs Lows Sharav lows

28

29 אפיק י ם סוף ציר מ ערבי ציר מערבי (2)

30 Synoptic Type RST - Eastern axis RST - Western axis RST - Central axis Weak Persian trough Medium Persian trough Strong Persian trough Highs to the east Highs to the west Highs to the north Highs over Israel Deep low to the east Deep low to the south Shallow low to south Deep low to the north Shallow low to the north Cold low to the west Shallow low to east Sharav low to west Sharav low over Israel Exceeding Days 477 days (~7 days/year) Extensive Exceeding Days 67 days (~1 days/year)