C. E. Jordan

Chemical composition of Asian continental outflow over the western Pacific: Results from Transport and Chemical Evolution over the Pacific (TRACE‐P)

[1] We characterize the chemical composition of Asian continental outflow observed during the NASATransport and Chemical Evolution over the Pacific (TRACE-P) mission during February–April 2001 in the western Pacific using data collected on the NASA DC-8 aircraft. A significant anthropogenic impact was present in the free troposphere and as far east as 150E longitude reflecting rapid uplift and transport of continental emissions. Five-day backward trajectories were utilized to identify five principal Asian source regions of outflow: central, coastal, north-northwest (NNW), southeast (SE), and west-southwest (WSW). The maximum mixing ratios for several species, such as CO, C2Cl4 ,C H3Cl, and hydrocarbons, were more than a factor of 2 larger in the boundary layer of the central and coastal regions due to industrial activity in East Asia. CO was well correlated with C2H2 ,C 2H6 ,C 2Cl4, and CH3Cl at low altitudes in these two regions (r 2 0.77–0.97). The NNW, WSW, and SE regions were impacted by anthropogenic sources above the boundary layer presumably due to the longer transport distances of air masses to the western Pacific. Frontal and convective lifting of continental emissions was most likely responsible for the high altitude outflow in these three regions. Photochemical processing was influential in each source region resulting in enhanced mixing ratios of O3, PAN, HNO3 ,H 2O2, and CH3OOH. The air masses encountered in all five regions were composed of a complex mixture of photochemically aged air with more recent emissions mixed into the outflow as indicated by enhanced hydrocarbon ratios (C2H2/CO 3 and C3H8/C2H6 0.2). Combustion, industrial activities, and the burning of biofuels and biomass all contributed to the chemical composition of air masses from each source region as demonstrated by the use of C2H2 ,C 2Cl4, and CH3Cl as atmospheric tracers. Mixing ratios of O3, CO, C2H2 ,C 2H6 ,S O2, and C2Cl4 were compared for the TRACE-P and PEM-West B missions. In the more northern regions, O3, CO, and SO2 were higher at low altitudes during TRACE-P. In general, mixing ratios were fairly similar between the two missions in the southern regions. A comparison between CO/CO2, CO/CH4 ,C 2H6/ C3H8 ,N Ox/SO2, and NOy/(SO2 + nss-SO4) ratios for the five source regions and for the 2000 Asian emissions summary showed very close agreement indicating that Asian emissions were well represented by the TRACE-P data and the emissions inventory. INDEX TERMS: 0365 Atmospheric Composition and Structure: Troposphere—composition and chemistry; 0368 Atmospheric Composition and Structure: Troposphere—constituent transport and chemistry; 0345 Atmospheric Composition and Structure: Pollution—urban and regional (0305)

Water‐soluble nitrogen at the New Hampshire sea coast: HNO3, aerosols, precipitation, and fog

An intensive sampling program was carried out from May 1994 through November 1997 on the shore of the Gulf of Maine in New Castle, New Hampshire. Daily (24 hour averages) samples of bulk aerosol and gas phase HNO 3 , precipitation, and 20 aerosol size distributions were obtained. Particulate NH 4 + and gas phase HNO 3 were the dominant water-soluble nitrogen species in the atmosphere. There was a summer peak in the mixing ratios of both of these species. Daily mixing ratios of HNO 3 and all aerosol species were highly variable, yet the annual averages tended to be similar from one year to the next. The concentrations of all the inorganic species we measured in precipitation were generally higher than those of two National Acid Deposition Program (NADP) coastal sites. In particular, the annual volume-weighted means for NO 3 - (22 - 27 μmol/L) and NH 4 + (11 - 17 μmol/L) were found to be 20% - 60% and 40% - 90% higher, respectively, than those reported from Cape Cod, Massachusetts. Nitrate was the dominant inorganic nitrogen ion in precipitation at New Castle. In autumn, concentrations of continentally derived species in precipitation decreased substantially while sea salts increased. There was insufficient NH 3 to fully neutralize HNO 3 and H 2 SO 4 in aerosols and precipitation. The overall atmospheric chemistry in this region was heavily dominated by anthropogenic pollution products. The samples collected were used in conjunction with 1000 hPa streamlines to classify sampled air masses according to their surface level transport and chemistry. Eight characteristic groups were defined; of these the three primary groups were polluted continental, clean continental, and marine. Highly variable mixing ratios of HNO 3 and aerosol species were observed within each group from day to day, yet each group had a unique average chemical signature. On average, the HNO 3 and aerosol mixing ratios observed in 1995 were roughly a factor of 2 lower than seen for the groups in other years. Overall, mixed conditions occurred in 42% of the samples, continental species were dominant in 37%, and marine species were dominant in 21%. Rain occurred frequently under sea-salt-dominant conditions; about 47% of the days classified as such had rain events. Fog chemistry and average aerosol chemical size distributions were evaluated based on which species dominated their chemical signatures, marine, continental, or a relatively even mixture of the two. Particulate NO 3 - was associated with sea-salt Na + in the coarse aerosol fraction peaking at approximately 4 μm in diameter. There was also a distinct secondary peak in the submicron fraction observed in air dominated by continental aerosols. Particulate NH 4 + was associated with non-sea-salt SO 4 2- (nss-SO 4 2- ), with the bulk of the NH 4 + present on particles in the 0.43 - 1.1 μm diameter range. Although nss-SO 4 2- was primarily found in the submicron size range, a substantial fraction (> 25%) was found in the supermicron range for all three cases. Chloride was depleted on average 25% in aerosols and 13% in precipitation with respect to sea-salt aerosols, with the deficit greatest for particles in the 1.1 - 3.3 μm and 9.0 - 25 μm diameter ranges.

Direct atmospheric deposition of water-soluble nitrogen to the Gulf of Maine

Measurements were made at New Castle, New Hampshire, on the shore of the Gulf of Maine from 1994 to 1997 to assess direct atmospheric deposition of water-soluble nitrogen to the surface waters of the gulf. Daily dry deposition was highly variable and ranged from ∼ 1 to 144 μmol N m -2 d -1 (median 16 μmol N m -2 d -1 ). Wet deposition dominated dry deposition, contributing 80-90% of the total flux annually. Wet deposition was also highly variable and ranged from 3 to 4264 μmol N m -2 d -1 (median 214 μmol N m -2 d -1 ). Fog water nitrogen deposition could contribute as much as large precipitation nitrogen deposition events, in excess of 500 μmol N m -2 d -1 . Dissolved organic nitrogen (DON) in precipitation constituted only a small fraction (3%) of the total precipitation nitrogen flux most of the year, except in spring where it comprised 14%, on average, of the total. The total atmospheric direct nitrogen (ADN) deposition numbers reported here do not include the contributions of fog and DON as they were not sampled regularly over the course of this study. The total ADN flux ranged from 1 to 4262 μmol N m -2 d -1 (median 23 μmol N m -2 d -1 ), depositing 52 mmol N m -2 yr -1 to the surface waters of the Gulf of Maine, 3% of the total N input to those waters annually. However, this deposition was highly episodic with events over 500 μmol N m -2 d -1 occurring in 8% of the days sampled but contributing 56% of the total measured flux and events in excess of 1000 μmol N m -2 d -1 occurring in 2% of the samples and contributing 22% of the total measured flux. It is these large events that may influence biological productivity of the Gulf of Maine. The annual wet deposition of inorganic N measured at New Castle exceeded that reported by two National Atmospheric Deposition Program (NADP) sites by 42% on average of that reported from Cape Cod, Massachusetts, and by 69% of that at Mt. Dessert Island, Maine. Estimates of the episodic atmospheric nitrogen flux to the surface waters of the Gulf of Maine suggest large deposition events could be sufficient to support substantial chlorophyll a production, especially under calm conditions.

Airborne sampling of aerosol particles: Comparison between surface sampling at Christmas Island and P-3 sampling during PEM-Tropics B

Bulk aerosol sampling of soluble ionic compounds from the NASA Wallops Island P-3 aircraft and a tower on Christmas Island during PEM-Tropics B provides an opportunity to assess the magnitude of particle losses in the University of New Hampshire airborne bulk aerosol sampling system. We find that most aerosol-associated ions decrease strongly with height above the sea surface, making direct comparisons between mixing ratios at 30 m on the tower and the lowest flight level of the P-3 (150 m) open to interpretation. Theoretical considerations suggest that vertical gradients of sea-salt aerosol particles should show exponential decreases with height. Observed gradients of Na+ and Mg 2+ , combining the tower observations with P-3 samples collected below 1 km, are well described by exponential decreases (r values of 0.88 and 0.87, respectively), though the curve fit underestimates average mixing ratios at the surface by 25%. Cascade impactor samples collected on the tower show that >99% of the Na+ and Mg 2+ mass is on supermicron particles, 65% is in the 1-6 micron range, and just 20% resides on particles with diameters larger than 9 microns. These results indicate that our airborne aerosol sampling probes must be passing particles up to at least 6 microns with high efficiency. We also observed that nss SO 2- 4 and NH 4 , which are dominantly on accumulation mode particles, tended to decrease between 150 and 1000 m, but they were often considerably higher at the lowest P-3 sampling altitudes than at the tower. This finding is presently not well understood.

Origins of aerosol chlorine during winter over north central Colorado, USA

The Nitrogen, Aerosol Composition, and Halogens on a Tall Tower campaign (February–March 2011) near Boulder, Colorado, investigated nighttime ClNO2 production and processing. Virtually all particulate Cl was in the form of ionic Cl−. The size distributions of Cl− and Na+ were similar, with most of the mass in the supermicrometer size fraction, suggesting primary sources for both. Median Cl− concentrations were about half those of Na+ and Ca2+ for particle diameters centered at 1.4 and 2.5 µm. To investigate potential sources of Na+ and Cl−, four cases were studied that featured the prevalence of Na+ and Cl− and different transport pathways based on FLEXible PARTicle dispersion model (FLEXPART) retroplumes. Estimates of supermicrometer Na+ particle lifetime against deposition indicate that long-range transport of marine aerosols could account for the observed Na+. However, measured molar ratios of Ca2+ to Na+ (0.143–0.588) compared to seawater (0.022) indicate significant contributions from crustal sources to the supermicrometer aerosol composition during these four case studies. Further, low molar ratios of Mg2+ to Na+ (0.007–0.098) relative to seawater (0.114) suggest that some of the Na+, and presumably associated Cl−, originated from non-sea-salt sources. The heterogeneous chemical composition of saline soils throughout the western U.S., along with the nonlinearity of wind-driven soil deflation as a function of various surface soil properties, precludes a quantitative apportionment of soil, marine, and anthropogenic sources to the observed coarse-fraction aerosol. Nonetheless, results suggest that deflation of saline soils was a potentially important source of particulate Cl− that sustained atmospheric ClNO2 production and associated impacts on oxidation processes over northern Colorado.