# Presentation: 798702

## Impact of East Asian summer monsoon on the air quality over China  

***EOS Aura Science Team Meeting***
_**Oct. 27-30, 2008**_

**Chun Zhao, Yuhang Wang, Qing Yang, Derek Cunnold *****Georgia Institute of Technology, Atlanta, GA*****Rong Fu*****University of Texas at Austin, Austin, TX*****Yunsoo Choi*****Jet Propulsion Laboratory, Pasadena, CA***

**Notes:**
Ok, welcome to be here. As we know, China is claimed with heavy air pollution issue in recent years. Today, I am going to talk about how east asian summer monsoon affect the air quality over China. Here, I would like to thank my advisor, qing yang for providing the OMI-MLS O3 data, Rong Fu for advise on monsoon study, and yunsoo choi for TES data process.

## Asian-Pacific Summer Monsoon System [Ding et al., 2005]: 

- Asian-Pacific Summer Monsoon System [*Ding et al.*, 2005]:
-  Indian Summer Monsoon (ISM)
-  Western North Pacific Summer Monsoon (WNPSM)
-  East Asian Summer Monsoon (EASM)

**Notes:**
First, let’s see what is East Asian summer monsoon. East Asian summer monsoon is one of the subsystems of Asian-Pacific summer monsoon system. Generally Asian-Pacific summer monsoon system can be divided into three subsystems: Indian summer monsoon, western north pacific summer monsoon, and east asian summer monsoon. East Asian monsoon affects East China, Korea and Japan. 

## EASM related rainy seasons over East China [Ding et al., 2005] : 

-  Pre-summer rainy season from mid-May to mid-June over South China.
-  Rapidly shift to the valley of the Yangtze River, initiating the Meiyu rainy season from mid-June to second week of July over central China.
-  Stay over North China from mid-July to early August.
-  Rapidly moves back to South China in the end of August or early September.

- mid-May

- mid-June

- mid-July

- end of August

- South China

- Central China

- North China

- South China

**Notes:**
One of characters of the monsoon weather system is precipitation. Generally, heavy rainfall is accompanied with East Asian summer monsoon over East China. the EASM related rainy seasons over East China can be divided into four stages based on the time period and location of its onset. At the beginning, EASM comes into south china from mid-May to mid-June. Then it rapidly shifts to the central China from from mid-June to mid-July. Afterwards, monsoon stays over North china until early August, and moves back to South China in the end of August. But we should know that this is the climatological feature. In different year, we may expect some difference.  

## EASM related rainy seasons over East China [Ding et al., 2005] : 

-  Pre-summer rainy season from mid-May to mid-June over South China.
-  Rapidly shift to the valley of the Yangtze River, initiating the Meiyu rainy season from mid-June to second week of July over central China.
-  Stay over North China from mid-July to early August.
-  Rapidly moves back to South China in the end of August or early September.

- mid-May

- mid-June

- mid-July

- end of August

- South China

- Central China

- North China

- South China

**Notes:**
One of characters of the monsoon weather system is precipitation. Generally, heavy rainfall is accompanied with East Asian summer monsoon over East China. the EASM related rainy seasons over East China can be divided into four stages based on the time period and location of its onset. At the beginning, EASM comes into south china from mid-May to mid-June. Then it rapidly shifts to the central China from from mid-June to mid-July. Afterwards, monsoon stays over North china until early August, and moves back to South China in the end of August. But we should know that this is the climatological feature. In different year, we may expect some difference.  

## EASM related rainy seasons over East China [Ding et al., 2005] : 

-  Pre-summer rainy season from mid-May to mid-June over South China.
-  Rapidly shift to the valley of the Yangtze River, initiating the Meiyu rainy season from mid-June to second week of July over central China.
-  Stay over North China from mid-July to early August.
-  Rapidly moves back to South China in the end of August or early September.

- mid-May

- mid-June

- mid-July

- end of August

- South China

- Central China

- North China

- South China

**Notes:**
One of characters of the monsoon weather system is precipitation. Generally, heavy rainfall is accompanied with East Asian summer monsoon over East China. the EASM related rainy seasons over East China can be divided into four stages based on the time period and location of its onset. At the beginning, EASM comes into south china from mid-May to mid-June. Then it rapidly shifts to the central China from from mid-June to mid-July. Afterwards, monsoon stays over North china until early August, and moves back to South China in the end of August. But we should know that this is the climatological feature. In different year, we may expect some difference.  

## EASM related rainy seasons over East China [Ding et al., 2005] : 

-  Pre-summer rainy season from mid-May to mid-June over South China.
-  Rapidly shift to the valley of the Yangtze River, initiating the Meiyu rainy season from mid-June to second week of July over central China.
-  Stay over North China from mid-July to early August.
-  Rapidly moves back to South China in the end of August or early September.

- mid-May

- mid-June

- mid-July

- end of August

- South China

- Central China

- North China

- South China

**Notes:**
One of characters of the monsoon weather system is precipitation. Generally, heavy rainfall is accompanied with East Asian summer monsoon over East China. the EASM related rainy seasons over East China can be divided into four stages based on the time period and location of its onset. At the beginning, EASM comes into south china from mid-May to mid-June. Then it rapidly shifts to the central China from from mid-June to mid-July. Afterwards, monsoon stays over North china until early August, and moves back to South China in the end of August. But we should know that this is the climatological feature. In different year, we may expect some difference.  

## Index of Asian Summer Monsoon (ASM) over East China in 2006 following Zhang et al., 2004, based on precipitation rate and vertical wind shear.

**Notes:**
This is the climatological 5-day mean rainfall over East China from April to Sep. Above the read dash line, it’s over China continent. As we can see the heavy rainfall over South China in May and first half of June, then it moves to North China in July. The rainfall comes back over South China in August. We should notice here the heavy rain over East China in April and early May, when the East Asian summer monsoon has not even start. So we can not use only the rainfall to decide the monsoon onset. Monsoon index is one direct factor related to the monsoon onset. We chose 2006 in this study. Here is the calculated Asian Summer Monsoon index over East China in 2006. East Asian monsoon comes into East China from the end of May, and dominates the southeast China in June and the whole east China in July, becomes weaker in August. Generally, consistent with the climatological feature. 

## How could EASM affect the chemical composition of troposphere?

-  As a sub-system of Asian-Pacific summer monsoon system, EASM significantly affects the distribution and transport of chemical tracers over Asia [e.g., *Kar et al*, 2004; *Jiang, et al.,* 2007; *Park et al.,* 2007]
-  By itself, EASM constrains the distribution of the chemical tracers over China, e.g, surface O3 seasonal variation [e.g., *He et al.,* 2008]

**Notes:**
How could EASM affect the chemical composition of troposphere? First, As a sub-system, it ....... Which is already shown by many previous studies using satellite measurements. Second, By itself, it constrains the distribution of the chemical tracers over China. The incursion of monsoon transports oceanic air with less pollutants to the polluted region over East China and initiates the rainy seasons, consequently causes lower pollutants concentrations such as O3 over East China in summer. This has been shown through sparse in-situ surface measurements over China. Here we are going to investigate monsoon impact in a big view using satellite data.

## Satellite measurementsTropospheric CO columns from MOPITT onboard the Terra satellite, CO concentrations from TES and tropospheric O3 columns derived from OMI and MLS onboard the Aura satellite.

REAM modelThe REAM model driven by WRF assimilated meteorological fields, and has a horizontal resolution of 70 km with 23 vertical layers below 10 hpa. Initial and boundary conditions for chemical tracers in REAM are obtained from the global simulation using the GEOS-CHEM model.

**REAM model**The REAM model driven by WRF assimilated meteorological fields, and has a horizontal resolution of 70 km with 23 vertical layers below 10 hpa. Initial and boundary conditions for chemical tracers in REAM are obtained from the global simulation using the GEOS-CHEM model.

## EASM impact shown in MOPITT tropospheric CO columns over East China:

-  Pre-monsoon CO column enhancements over East China
-  CO column enhancement regions over East China disappear during monsoon period
-  CO column enhancements re-emerge after the monsoon

**Notes:**
In the following slides, the figures are shown with satellite measurements on the left and model simulation on the right. First let’s look at the CO columns from MOPITT measurements over East China. The black line in the middle of each plot is to make the south and north China clear.

## EASM impact shown in TES tropospheric CO concentration over East China (110o-120oE):

- EASM impact shown in TES tropospheric CO concentration over East China (110o-120oE):
-  Boundary CO concentration decreases during monsoon period, and re-emerges afterwards over Southeast China

**Notes:**
(The underestimate of the ozone could be from the CO emissions in REAM)

## EASM impact shown in OMI-MLS tropospheric O3 columns over East China:

- EASM impact shown in OMI-MLS tropospheric O3 columns over East China:
- Pre-monsoon tropospheric O3 column enhancements over Southeast China
-  Monsoon driven tropospheric O3 columns decreases over Southeast China
-  O3 enhancement during monsoon over West China

**Notes:**
Surface measurements observed the spring maximum and summer minimum O3 concentration feature over East China. Up to the present, the O3 spring maximum could be possibly accounted by the combination stratospheric intrusion and regional photochemical production. The observed summer minimum of surface O3 over East Asia was attributed to the incursion of monsoon which transports oceanic air with less O3 to the region and causes lower O3 concentration. Surface O3 measurements in different sites also indicate that East Asian monsoon play a central role in producing the latitudinal differences in O3 seasonality.

## EASM impact shown in OMI-MLS tropospheric O3 columns over East China:

- EASM impact shown in OMI-MLS tropospheric O3 columns over East China:
- Pre-monsoon tropospheric O3 column enhancements over Southeast China
-  Monsoon driven tropospheric O3 columns decreases over Southeast China
-  O3 enhancement during monsoon over West China

**Notes:**
The relatively large discrepancy between REAM and the Aura OMI-MLS tropospheric ozone columns (TCOs) at high latitudes might be associated with the increased uncertainties in the OMI-MLS TCO data at these regions. In the derivation of the OMI-MLS TCOs, the stratospheric ozone column contributions from the layer between the lowest utilized level of the MLS data (215 mbar) and the tropopause were obtained from mapping of SAGE II ozone profile measurements (Yang et al., 2007).  The uncertainties of the estimated column amounts in this layer may increase at high latitudes due to the lower tropopause heights and the possibly less reliable ozone mapping relationships resulting from the smaller numbers of available SAGE II profile measurements at high latitudes. 

## EASM impact shown in OMI-MLS tropospheric O3 columns over East China:

- EASM impact shown in OMI-MLS tropospheric O3 columns over East China:
- Pre-monsoon tropospheric O3 column enhancements over Southeast China
-  Monsoon driven tropospheric O3 columns decreases over Southeast China
-  O3 enhancement during monsoon over West China

**Notes:**
We also find the west China ozone enhancement, which is already claimed by several previous studies with surface measurements. OMI-MLS tends to overestimate O3 columns over high plain regions compared with model. We have the same issue over North America.

## Slide 15

**Notes:**
We have seen the monsoon impact on the O3 columns. Here we show that the surface ozone is also strongly constrained by monsoon. Let’s focus on the monsoon pass over period with the box from mid-June and early July. The simulated latitudinal dependent surface O3 summer variation correlates with the monsoon driven precipitation pattern. 

## Summary and future work:

- Satellite measurements show that Asian Monsoon strongly constrains air pollutant distributions over East China in summer. In the monsoon season, ventilation and scavenging are faster while photochemical processing is slower, resulting lower pollutant levels.
- MOPITT and TES CO measurements show CO enhancement regions over Southeast China disappear with the onset of the monsoon and re-emerge afterwards.
- The OMI-MLS tropospheric O3 columns show the late spring O3 enhancements and summer O3 decreases over East China. The simulated surface O3 summer variation correlates with the monsoon driven precipitation pattern.
- Enhancement of tropospheric O3 over western China may be driven by transport of stratospheric O3.

**Notes:**
summary