Urban and On-Road Emissions: Underappreciated Sources of Atmospheric Ammonia

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1 Urban and On-Road Emissions: Underappreciated Sources of Atmospheric Ammonia Mark Fenn 1, Susan Schilling 1, Andrzej Bytnerowicz 1, Michael Bell 2, James Sickman 3, Ken Hanks 1 and Linda Geiser 4 1 US Forest Service, Pacific Southwest Research Station 2 National Park Service, Air Resources Division 3 Univ. of California, Riverside, Dept. of Environ. Sci. 4 US Forest Service, Watershed, Fish, Wildlife, Air & Rare Plants, Washington, DC PSW Res. Stn.

2 Why Talk About NH x Deposition in CA & Elsewhere? Increasing data showing high NH x in areas traditionally dominated by NO y Modern light duty and newer heavy duty vehicles an important source of NH 3 High sensitivity of lichens and vegetative communities to NH 3 and NH4 deposition Observations of increasing relative importance of NH x compared to NO x in many locations, even in the absence of major agricultural sources

3 NH 3 Emissions from Modern Heavy Duty Vehicles Heavy-duty vehicles now include a mix of natural gas engines with three-way catalytic converters and diesel engines equipped with selective catalytic reduction (SCR), resulting in NH 3 emissions For the latter device, aqueous urea is injected as a reductant for NO x control Emission rates of NH 3 for heavy-duty vehicles using natural gas engines equipped with threeway catalytic converters had NH 3 emission rates that were 5-10 times greater than light duty vehicles (Bishop et al. 2011, Thiruvengadam et al. 2016)

4 A recent example of the trend of increasing NH 3 production by additional types of vehicles and engines.

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6 General Rule: Conditions and emissions control mechanisms that result in highly effective NO x reduction result in greater NH 3 production and emissions

7 Percent NH 3 Emissions From On-Road Sources (by county)

8 On-road NH 3 emission (2012) Agricultural NH 3 emissions (NEI-2014)

9 Cumulative Distribution of US Counties in Relation to the Percent NH 3 Emissions From On- Road Sources

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11 Ag-affected NADP/NTN Sites: Trends in NH 4, NO 3 and SO 4 concentrations

12 Urban-affected NADP/NTN Sites: Trends in NH 4, NO 3 and SO 4 concentrations

13 Throughfall Site N Deposition (kg/ha/yr) NH4-N:NO3-N Portland, Forest Park Portland, Zoo Eugene, Hendrix Park Seattle, Seward Park Open Site Importance of NH 4 + Deposition in Urban OR and WA MEAN: 1.0 Portland, Forest Park Portland, Zoo Eugene, Hendrix Park Seattle, Seward Park MEAN: 2.3

14 NH 4 :NO 3 in Throughfall Under Shrubs: LA Basin

15 IER throughfall collector for sampling under shrub canopies

16 Lake Tahoe Basin---Affected by in-basin urban and onroad N emissions

17 Lake Tahoe: Throughfall Deposition of N 4 Annual Throughfall N Deposition in the Tahoe Basin ( to ) Throughfall N Deposition (kg/ha) NH4-N NO3-N 0 Angora Genoa Peak 7k Genoa Peak 8k Genoa Peak 9k Lower Blackwood Creek Thunderbird Lodge Upper Incline Valhalla Watson Creek

18 Lake Tahoe Basin: NH 4 + Deposition vs. Atmospheric NH 3 Concentrations NH 3 -N (ug m -3 ) y = x r 2 = Throughfall NH4-N (kg ha -1 yr -1 ) NH3-N (ug m -3 ) y = x r 2 = Bulk Deposition NH4-N (kg ha -1 yr -1 )

19 Values for δ 15 NH 4 + in bulk deposition in Lake Tahoe

20 Gaseous Pollutants: NH 3 and NO y Temporal Trends at Rural Sites in Southern California

21 Concentrations of NH 3 and NO 2 Near Highways in the San Francisco Bay Area

22 N gaseous pollutant deposition to a California grassland near a major highway (280) in the coastal San Francisco peninsula and in near-urban sites HNO3 NH3 NO2 kg-n/ha EW1 EW2 EW3 JR RC TH KC1 KC2

23 CONCLUSIONS As a rule, stringent NO x controls lead to NH 3 production from on-road and industrial sources Proportion of on-road N emissions as NH 3 is increasing due to decreasing emissions of NO x and growing segment of the vehicle fleet emitting NH 3 NH 4 -N deposition in urban and near-urban sites is increasingly greater than NO 3 -N Urban NH 3 emissions have strong effects on aerosol production (e.g., PM 2.5 )

24 CONCLUSIONS On-road NH 3 emissions contribute 50% of total NH 3 emissions in many counties Such on-road and urban NH 3 emissions are not widely acknowledged Deposition/atmospheric exposure footprint of on-road NH 3 emissions not fully understood In many areas both ag and on-road emissions of NH 3 are important contributors to environmental and ecological impacts