Slide 1

Transport and chemical processing of mercury during long-range transport in the Pacific

by Dan Jaffe University of Washington

Acknowledgements:

My research team

NIES (Tsukuba, Japan), TMU (Tokyo, Japan), OSU, Frontier Geosciences

Mt. Bachelor Ski Corporation (Oregon)

EPA: ORD, OIA and STAR program for support

Slide 2

Motivation• Unacceptably high levels of Hg in some

species of fish in most states of the U.S. (especially tuna, swordfish and bass);

• Health risk from eating significant amounts of these fish, especially for children and pregnant women;

• EPA has an on-going process to address high levels of Hg in fish by reducing domestic Hg emissions;

• New rules to reduce Hg emissions from power plants due out March 15, 2005.

Slide 3

But….

• There is significant uncertainty over the amount of Hg deposition that is subject to domestic regulations. Natural sources can’t be controlled. Non-US sources can’t be controlled without an international agreement.

• Bullock (2004) gives the international contribution as 30-70%;

• Seigneur et al. 2004) cites the Asian contribution to U.S. deposition at 5-36 %.

Slide 4

GoalsTo understand the long range transport of speciated Hg in the Pacific;

To quantify the contribution that transport makes on the atmospheric Hg budget of North America;

To quantify the contribution that transport makes on the Hg deposition budget of North America.

Slide 5

Vector winds700 mb, April mean

Slide 6

Global anthropogenic Hg emissions for 1990, 1x1 degree grid (Source: AMAP)

Year 2000 global emissions of Hg are ~2000 metric tons/year, largely as Hg(0). More then half of the emissions are from Asia.

Slide 7

GoalsWhat is the atmospheric flux of Hg that arrives to the US from distant sources? What is the speciations and sources of this Hg?Can we verify the large Hg emissions that are associated with Asian sources?What is the chemical processing of Hg during transport?What are the sources of Hg in deposition?What are the long-term implications and trends in these sources?

Slide 8

Our observations sites in the Northwestern U.S.

In addition, we use satellite data, global transport models and data from other regional networks.

2.7 km asl

Slide 9

Spring 2004 Experiment: Simultaneous Observations at Mt.Bachelor and Okinawa

MBO

Okinawa

Okinawa: Hg0,RGM, PHg (Tekran 2537, 1130, 1135), CO, O3, aerosols, etc.

MBO: Total Hg0 (Tekran 2537 w/high temperature quartz inlet), CO, O3, aerosols, etc.

Mauna Loa

Slide 10

For 2 long-lived components, the ratio of emissions is preserved during transit.

Xo, Yo

ΔY/ΔX = Yo/Xo

Where Δ refers to the enhancement over background

Xbg, Ybg

Slide 11

Definition of an “event”

Time

Conc.“Background”

(natural+anthropogenic)

“Event”

Slide 12

Scatter plot of two components during an “event”

Y

X

slope = ΔY/ΔX = Yo/Xo (emission ratio)

Assumptions:

1) No chemical or physical loss, only dilution;2) Constant emission source with fixed Yo/Xo ratio;3) Constant background concentrations.

For this work we will use CO and Hg(0), which both have lifetimes >> Pacific transit time.

This reflects a linear combination of emissions + background air.

Slide 13

CO and Hg Emissions

CO emissions for 2001

Hg emissions for 2000

Note that during the NASA TRACE-P experiment, the Palmer CO inventory was extensively evaluation against observations. As a result of this evaluation, the Asian CO inventory was increased by ~30% over previous inventories, most likely due to an underestimate of residential coal combustion in Asia.

Region

CO emissions

(x 106

m.t./yr)

Total Hg emissions (m.t./yr)

Hg0 emissions (m.t./yr)

Tot Hg/CO (molar) Hg0/CO (molar)

Washington 1.86 0.22 0.12 1.6 x 10-8 8.5 x 10-9 Oregon 1.82 0.24 0.13 1.8 x 10-8 9.4 x 10-9

California 7.35 2.6 1.37 4.8 x 10-8 2.5 x 10-8 Asia 328 1204 770 5.0 x 10-7 3.2 x 10-7

China 168 604 387 4.9 x 10-7 3.1 x 10-7

Slide 14

1

2

3 4

5

6

Slide 15

Correlation coefficients (R2) CO Hg0 RGM PHg

CO *** 0.84 0.01 0.25

Hg0 *** *** 0.04 0.24

Summary of Okinawa data Hgo

(ng/m3) RGM

(pg/m3)

PHg

(pg/m3)

CO (ppbv)

Mean 2.04 4.51 3.04 214.9

Median 1.99 2.50 2.36 199.8

Min 1.37 0.12 0.10 98.3

Max 4.74 32.49 16.45 761.4

Slide 16

Hg0 vs CO (all data)

Slide 17

CO-Hg correlation during an event

Slide 18

Okinawa back trajectory: event 5

Slide 19

Summary of Okinawa events

Event # Start dateDel Hg/Del CO

(ng/m3/100 ppbv)

Source region (Hysplit) %RGM+PHg

Export1 29-Mar-04 0.43 China/E.Asia 1.52 1-Apr-04 0.55 China 2.53 7-Apr-04 0.72 China/Korea 2.64 13-Apr-04 0.48 China/E.Asia 2.25 18-Apr-04 0.73 China 2.96 26-Apr-04 0.39 China/Korea 0.7

Mean 0.56 +/- 0.15 2.1

Slide 20

Mt. Bachelor back trajectory, April 26, 2004

Slide 21

Hg transport to North America: April 25th, 2004

This is one of the largest Asian LRT events we have ever seen (ΔCO > 100 ppbv). ΔHg/ΔCO=0.50 ng/m3/100 ppbv

Slide 22

Observed ΔHg/ ΔCO ratios in Asian plumes

Hg/CO ratio appears to be good marker for Asian plume

Location ΔHg/ΔCO (molar) x 107

Okinawa 6.2 +/- 1.7 (n=6)

Mt.Bachelor 5.5 (n=1)

Shanghai plume(Friedli et al., 2004)

6.2 (n=1)

Slide 23

Comparison of observed Hg/CO ratio with Asian emission inventory (x 107)

There is a significant discrepancy between the emisions inventory and the observed ratio.

Location Hg0/CO (molar)Okinawa-observed

6.2

Emissions inventory

Hg0/CO (molar) Total Hg/CO (molar)

China 3.1 4.9

Asia 3.2 5.0

Year 2000 emissions from Pacyna 2003

Slide 24

Possible causes for this discrepancy:• Underestimate of the industrial or domestic Hg emissions;• Natural emissions;• Re-emission of previously deposited Hg;• Too low a ratio of Hg0/total Hg in the inventory;• Conversion of RGM to Hg0 during transport;

Significant opportunity to improve our understanding!

Explanations/HypothesesUsing the observed Hg0/CO ratio, and the known CO emisions, we calculate Hg0 emissions from Asia of 1460 mt/year (+/-30%);

This can be compared to 770 mt/year in the Pacyna et al., 2003 inventory.

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Other questions to ask of the Okinawa data• Why do some episodes of LRT to Okinawa have enhanced Particulate Hg, but

not others?• What role does the aerosol type play in RGM and PHg production?• Are the variations in the Hg/CO ratios for individual events consistent with the

trajectory source region and the 1ox1o Hg and CO emission inventories?• Is their evidence of diurnal RGM production? Is their a relationship between

RGM production and ozone production?• Why does RGM show peaks when all other parameters are low?• Are their known chemical mechanisms that could reconvert RGM and PHg to

Hg0?• How well can GCTM’s simulate these observations and what does this tell us

about the relative importance of industrial, natural and re-emission sources?

Slide 26

1) Observations of Hg, CO and other species at Okinawa and Mt. Bachelor Oregon confirm substantial emissions of Hg from Asia;

2) The vast majority of the Hg outflow is as Hg0;3) There is a significant discrepancy between the observed Hg0/CO

ratio in Asian plumes and the industrial emission inventory of Pacyna et al., 2003. This could be due to an underestimate of the industrial or domestic emissions, natural emissions, re-emission of previously deposited Hg, too low a ratio of Hg0/total Hg in the inventory or possibly conversion of RGM to Hg0 during transport;

4) We have detected LRT of mercury from Asia to the U.S. Most likely, the mercury is largely in the Hg0 form;

5) Future observations at Mt.Bachelor will provide data on speciated Hg concentrations in the free troposphere and during LRT.

Summary