Diurnal Variability of Aerosols Observed by Ground-based

NetworksQian Tan (USRA), Mian Chin (GSFC), Jack Summers (EPA), Tom Eck (GSFC), Hongbin Yu (UMD), Caterina Tassone (NOAA), Yan Zhang

(MSU), EPA/AQS, NASA/AERONET, NOAA/NCDC

Outline Diurnal variability of surface PM2.5

How significant Variations on other time scales.

Linkage between diurnal cycle of surface PM2.5 and column AOT Correlation on their diurnal cycles Possible meteorological impacts

Measuring Aerosol Variations in Different Ways

Day 1 Day 2 Day 3 Day 4 Day 5 ……… Day n

Day-to-day variation (EPA

24-hr filter)

Sun-synchronized orbitBetter spatial coverage

Geo-stationary orbit

EPA hourly obs.

Aerosols Diurnal Variation Continuous ground based

observations. EPA AQS hourly PM2.5 observations.

Diurnal variation vs daily average Comparison to seasonal variations.

Averaged PM 2.5 Diurnal VariationsPM

2.5

(ug/

m^3

)

Max-Min

Std. Dev

2004 2005 2006 2007

Significant diurnal variation is observed: ~ 15-22 ug/m3, EPA PM2.5 standard: 35 ug/m3 for 24hr, 15 ug/m3 annual average.

Compared with Daily AveragePe

rcen

tage

(%

) (Max-Min) / Mean

Std. Dev/ Mean

Variations of surface PM2.5 within a day is comparable to its daily mean:

Maximum-minimum is 120-170% of its meanStandard deviation is ~30-50%.

2004 2005 2006 2007

Seasonal & Year-Year DifferenceMax-Min Std

Dev

On average, the standard deviation of PM2.5 within a day

is comparable to the seasonal variation.

Co-located PM2.5 and AOT Using column AOT, i.e. what satellites

observe, to estimate the surface concentration of PM2.5 (criteria pollutant) Chu et al., (2003), Wang & Christopher (2003), Engel-

Cox (2004), Al-Saadi et al., (2005),…, Hoff & Christopher (2009)

Co-located AERONET and AQS observations New York City (CCNY) Baltimore (MD Science Center) Houston (University of Houston) Fresno (California)

Within 8km. Hourly data available Close by hourly meteorological & PBL observations

Day-to-Day PM2.5 vs AOT

On daily based, AOT shows good correspondence with surface PM2.5 concentration. Their correlation has large spatial differences (both r2 and slope).

Diurnal Cycle of PM2.5 & AOT -- Houston

PM2.5 shows clearer diurnal pattern, it changes with season.AOT diurnal pattern is less pronounced, larger seasonal variationDaily PM2.5 minimum is at noon time during fall and winter.

Correlation between AOT and PM2.5 on finer temporal frequency

€

AOD =PM2.5∗H∗f (RH)∗3Qext / dry4ρ reff

= PM2.5∗H∗S

Koelemeijer et al., 2006; Hoff & Christopher (2009)

Causes of variationsPM2.5 emissions, chemistry, deposition, dynamics, … AOT all of above

aerosol optical property

compositionsize and shape

aerosol vertical profilePBLlocal, regional, and long range transport

other factors clouds, (surface albedo)solar zenith angle

Diurnal Variation of PBL

PBL peaks in the early afternoonPBL is higher in summer (in Houston, less seasonal difference)

PBL vs. PM2.5Houston Baltimore New York

City

Winter

In winter, if PBL is high, then PM2.5 will be low -- in Houston, the minimum PM2.5 occurred around noon time.

AOT vs. PM 2.5 * PBL

R2 = 0.39

(2010)

R2=0.26

When PBL is high (>1000m), AOT is more correlated with PM2.5 R2 = 0.

51

PBL > 1000m

AOT vs PM2.5 * PBL *f(RH)R2 = 0.17

R2 = 0.40

R2 = 0.064

* F (RH)

R2 = 0.42

All PBL condition

PBL >1000m

+ surface RH

1. Low PBL will degrade correlation between AOT and PM2.52. When PBL is high, it is more likely to estimate PM2.5 using

AOT.

Conclusion Significant daily variation is observed

in surface PM2.5 concentration. Daily average of PM2.5 and AOT is

correlated well at urban sites. Diurnal cycle of PM2.5 and AOT is

different. better correlated when PBL is high

Extra slides

Diurnal Cycle of PM2.5 and AOT -- NYC

PM2.5 diurnal variation follow emission (traffic) pattern, & PBLAOT diurnal pattern is less pronounced, large seasonal variationNo clear pattern in summer months.

Correlation between AOT and PM2.5 Many studies to explore the linkage

between the two Using column AOT, i.e. what satellite can

observe, to estimate the surface concentration of PM2.5 (criteria pollutant) Chu et al., (2003), Wang & Christopher (2003), Engel-

Cox (2004), Al-Saadi et al., (2005),…, Hoff & Christopher (2009)