The SASS Ozone and Nitrogen Oxides Experiment (SONEX) over the North Atlantic during October/November 1997 offered an excellent opportunity to examine the budget of reactive nitrogen in the upper ...troposphere (8–12 km altitude). The median measured total reactive nitrogen (NOy) mixing ratio was 425 parts per trillion by volume (pptv). A data set merged to the HNO3 measurement time resolution was used to calculate NOy (NOy sum) by summing the reactive nitrogen species (a combination of measured plus modeled results) and comparing it to measured NOy (NOy meas.). Comparisons were done for tropospheric air (O3 <100 parts per billion by volume (ppbv)) and stratospherically influenced air (O3 > 100 ppbv) with both showing good agreement between NOy sum and NOy meas. (slope >0.9 and r² ≈ 0.9). The total reactive nitrogen budget in the upper troposphere over the North Atlantic appears to be dominated by a mixture of NOx (NO + NO2), HNO3, and PAN. In tropospheric air median values of NOx/NOy were ≈ 0.25, HNO3/NOy ≈ 0.35 and PAN/NOy ≈ 0.17. Particulate NO3− and alkyl nitrates together composed <10% of NOy, while model estimated HNO4 averaged 12%. For the air parcels sampled during SONEX, there does not appear to be a large reservoir of unidentified NOy compounds.
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We present the first data on the concentration of sea-salt aerosol throughout
most of the depth of the troposphere and over a wide range of latitudes,
which were obtained during the Atmospheric ...Tomography (ATom) mission.
Sea-salt concentrations in the upper troposphere are very small, usually less
than 10 ng per standard m3 (about 10 parts per trillion by mass) and
often less than 1 ng m−3. This puts stringent limits on the
contribution of sea-salt aerosol to halogen and nitric acid chemistry in the
upper troposphere. Within broad regions the concentration of sea-salt aerosol
is roughly proportional to water vapor, supporting a dominant role for wet
scavenging in removing sea-salt aerosol from the atmosphere. Concentrations
of sea-salt aerosol in the winter upper troposphere are not as low as in the
summer and the tropics. This is mostly a consequence of less wet scavenging
in the drier, colder winter atmosphere. There is also a source of sea-salt
aerosol over pack ice that is distinct from that over open water. With a
well-studied and widely distributed source, sea-salt aerosol provides an
excellent test of wet scavenging and vertical transport of aerosols in
chemical transport models.
New techniques have recently been developed and applied to capture reactive
nitrogen species, including nitrogen oxides (NOx=NO+NO2),
nitrous acid (HONO), nitric acid (HNO3), and particulate nitrate
...(pNO3-), for accurate measurement of their isotopic composition.
Here, we report – for the first time – the isotopic composition of HONO
from biomass burning (BB) emissions collected during the Fire Influence on
Regional to Global Environments Experiment (FIREX, later evolved into
FIREX-AQ) at the Missoula Fire Science Laboratory in
the fall of 2016. We used our newly developed annular denuder system (ADS),
which was verified to completely capture HONO associated with BB in
comparison with four other high-time-resolution concentration measurement
techniques, including mist chamber–ion chromatography (MC–IC), open-path
Fourier transform infrared spectroscopy (OP-FTIR), cavity-enhanced
spectroscopy (CES), and proton-transfer-reaction time-of-flight mass
spectrometry (PTR-ToF). In 20 “stack” fires (direct emission within ∼5 s of
production by the fire) that burned various biomass materials from the
western US, δ15N–NOx ranges from −4.3 ‰ to +7.0 ‰, falling near the
middle of the range reported in previous work. The first measurements of
δ15N–HONO and δ18O–HONO in biomass burning smoke
reveal a range of −5.3 ‰ to +5.8 ‰
and +5.2 ‰ to +15.2 ‰,
respectively. Both HONO and NOx are sourced from N in the biomass fuel,
and δ15N–HONO and δ15N–NOx are strongly
correlated (R2=0.89, p<0.001), suggesting HONO is directly
formed via subsequent chain reactions of NOx emitted from biomass
combustion. Only 5 of 20 pNO3- samples had a sufficient amount
for isotopic analysis and showed δ15N and δ18O of
pNO3- ranging from −10.6 ‰ to −7.4 ‰ and +11.5 ‰ to
+14.8 ‰, respectively. Our δ15N of NOx, HONO, and pNO3- ranges can
serve as important biomass burning source signatures, useful for
constraining emissions of these species in environmental applications. The
δ18O of HONO and NO3- obtained here verify that our method
is capable of determining the oxygen isotopic composition in BB plumes. The
δ18O values for both of these species reflect laboratory conditions
(i.e., a lack of photochemistry) and would be expected to track with the
influence of different oxidation pathways in real environments. The methods
used in this study will be further applied in future field studies to
quantitatively track reactive nitrogen cycling in fresh and aged western US
wildfire plumes.
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Brown carbon (BrC) consists of particulate organic species that preferentially absorb light at visible and ultraviolet wavelengths. Ambient studies show that as a component of aerosol particles, BrC ...affects photochemical reaction rates and regional to global climate. Some organic chromophores are especially toxic, linking BrC to adverse health effects. The lack of direct measurements of BrC has limited our understanding of its prevalence, sources, evolution, and impacts. We describe the first direct, online measurements of water-soluble BrC on research aircraft by three separate instruments. Each instrument measured light absorption over a broad wavelength range using a liquid waveguide capillary cell (LWCC) and grating spectrometer, with particles collected into water by a particle-into-liquid sampler (CSU PILS-LWCC and NOAA PILS-LWCC) or a mist chamber (MC-LWCC). The instruments were deployed on the NSF C-130 aircraft during WE-CAN 2018 as well as the NASA DC-8 and the NOAA Twin Otter aircraft during FIREX-AQ 2019, where they sampled fresh and moderately aged wildfire plumes. Here, we describe the instruments, calibrations, data analysis and corrections for baseline drift and hysteresis. Detection limits (3σ) at 365 nm were 1.53 Mm−1 (MC-LWCC; 2.5 min sampling time), 0.89 Mm−1 (CSU PILS-LWCC; 30 s sampling time), and 0.03 Mm−1 (NOAA PILS-LWCC; 30 s sampling time). Measurement uncertainties were 28 % (MC-LWCC), 12 % (CSU PILS-LWCC), and 11 % (NOAA PILS-LWCC). The MC-LWCC system agreed well with offline measurements from filter samples, with a slope of 0.91 and R2=0.89. Overall, these instruments provide soluble BrC measurements with specificity and geographical coverage that is unavailable by other methods, but their sensitivity and time resolution can be challenging for aircraft studies where large and rapid changes in BrC concentrations may be encountered.
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Distributions of aerosol‐associated soluble ions over much of the South Pacific were determined by sampling from the NASA DC‐8 as part of the Pacific Exploratory Mission (PEM) Tropics campaign. The ...mixing ratios of all ionic species were surprisingly low throughout the free troposphere (2–12 km), despite the pervasive influence from biomass burning plumes advecting over the South Pacific from the west during PEM‐Tropics. At the same time, the specific activity of 7Be frequently exceeded 1000 fCi m−3 through much of the depth of the troposphere. These distributions indicate that the plumes must have been efficiently scavenged by precipitation (removing the soluble ions), but that the scavenging must have occurred far upwind of the DC‐8 sampling regions (otherwise 7Be activities would also have been low). This inference is supported by large enhancements of HNO3 and carboxylic acids in many of the plumes, as these soluble acidic gases would also be readily scavenged in any precipitation events. Decreasing mixing ratios of NH4+ with altitude in all South Pacific regions sampled provide support for recent suggestions that oceanic emissions of NH3 constitute a significant source far from continents. Our sampling below 2 km reaffirms the latitudinal pattern in the methylsulfonate/non‐sea‐salt sulfate (MSA/nss SO4=) molar ratio established through surface‐based and shipboard sampling, with values increasing from <0.05 in the tropics to nearly 0.6 at 70°S. However, we also found very high values of this ratio (0.2–0.5) at 10 km altitude above the intertropical convergence zone near 10°N. It appears that wet convective pumping of dimethylsulfide from the tropical marine boundary layer is responsible for the high values of the MSA/nss SO4= ratio in the tropical upper troposphere. This finding complicates use of this ratio to infer the zonal origin of biogenic S transported long distances.
In this paper, we investigate the role of in situ new particle production in the central Canadian sub‐Arctic and Arctic as part of the TOPSE experiment. Airborne measurements conducted primarily in ...the free troposphere were made from 50° to 90°W longitude and 60° to 85°N latitude during the period from February to May 2000. Data pertinent to this paper include 3–4 nm diameter (Dp) particles, ultrafine condensation nuclei (Dp > 3 nm), fine particles (0.2 < Dp < 3 μm), and the possible nucleation precursor, sulfuric acid, and its precursor, sulfur dioxide. For data averaged over this period, most species showed little evidence for a latitudinal trend. Fine aerosol number concentrations, however, showed a slight increase with latitude. The evolution of various species concentrations over the period of the study show that fine particles also had a consistent temporal trend, increasing at all altitudes from February to May, whereas sulfur dioxide at the surface tended to peak in late March. Ultrafine condensation nuclei and 3–4 nm particles showed no temporal trends. Little evidence for in situ new particle production was observed during the study, except for one atypical event where SO2 concentrations were 3.5 ppbv, 2 orders of magnitude higher than typical levels. This paper cannot address the question of whether the observed condensation nuclei were produced in situ by a low particle production rate or transported from lower latitudes.
We report here measurements of the acidic gases nitric (HNO3), formic (HCOOH), and acetic (CH3COOH) over the western Pacific basin during the February‐March 1994 Pacific Exploratory Mission‐West ...(PEM‐West B). These data were obtained aboard the NASA DC‐8 research aircraft as it flew missions in the altitude range of 0.3–12.5 km over equatorial regions near Guam and then further westward encompassing the entire Pacific Rim arc. Aged marine air over the equatorial Pacific generally exhibited mixing ratios of acidic gases <100 parts per trillion by volume (pptv). Near the Asian continent, discrete plumes encountered below 6 km altitude contained up to 8 parts per billion by volume (ppbv) HNO3 and 10 ppbv HCOOH and CH3COOH. Overall there was a general correlation between mixing ratios of acidic gases with those of CO, C2H2, and C2Cl4, indicative of emissions from combustion and industrial sources. The latitudinal distributions of HNO3 and CO showed that the largest mixing ratios were centered around 15°N, while HCOOH, CH3COOH, and C2Cl4 peaked at 25°N. The mixing ratios of HCOOH and CH3COOH were highly correlated (r2 = 0.87) below 6 km altitude, with a slope (0.89) characteristic of the nongrowing season at midlatitudes in the northern hemisphere. Above 6 km altitude, HCOOH and CH3COOH were marginally correlated (r2 = 0.50), and plumes well defined by CO, C2H2, and C2Cl4 were depleted in acidic gases, most likely due to scavenging during vertical transport of air masses through convective cloud systems over the Asian continent. In stratospheric air masses, HNO3 mixing ratios were several parts per billion by volume (ppbv), yielding relationships with O3 and N2O consistent with those previously reported for NOy.
This paper describes the large‐scale distributions of HNO3, HCOOH, and CH3COOH over the central and South Pacific basins during the Pacific Exploratory Mission‐Tropics (PEM‐Tropics) in austral ...springtime. Because of the remoteness of this region from continental areas, low part per trillion by volume (pptv) mixing ratios of acidic gases were anticipated to be pervasive over the South Pacific basin. However, at altitudes of 2–12 km over the South Pacific, air parcels were encountered frequently with significantly enhanced mixing ratios (up to 1200 pptv) of acidic gases. Most of these air parcels were centered in the 3–7 km altitude range and occurred within the 15°−65°S latitudinal band. The acidic gases exhibited an overall general correlation with CH3Cl, PAN, and O3, suggestive of photochemical and biomass burning sources. There was no correlation or trend of acidic gases with common industrial tracer compounds (e.g., C2Cl4 or CH3CCl3). The combustion emissions sampled over the South Pacific basin were relatively aged exhibiting C2H2/CO ratios in the range of 0.2–2.2 pptv/ppbv. The relationships between acidic gases and this ratio were similar to what was observed in aged air parcels (i.e., >3–5 days since they were over a continental area) over the western North Pacific during the Pacific Exploratory Mission‐West Phases A and B (PEM‐West A and B). In the South Pacific marine boundary layer a median C2H2/CO ratio of 0.6 suggested that this region was generally not influenced by direct inputs of biomass combustion emissions. Here we observed the lowest mixing ratios of acidic gases, with median values of 14 pptv for HNO3, 19 pptv for HCOOH, and 18 pptv for CH3COOH. These values were coincident with low mixing ratios of NOx(<10 pptv), CO (≈50 parts per billion by volume (ppbv)), O3 (< 20 ppbv), and long‐lived hydrocarbons (e.g., C2H6 <300 pptv). Overall, the PEM‐Tropics data suggest an important influence of aged biomass combustion emissions on the distributions of acidic gases over the South Pacific basin in austral springtime.
Although allergy to sunscreen represents a small proportion (< 1%) of allergic contact dermatitis reactions in North America, it is one of the most common causes of photoallergy. The epidemiology and ...clinical characteristics of sunscreen allergy are summarized in this review. In addition, a detailed discussion of specific chemical sunscreen allergens is provided.
Abstract
Lightning is one of the most important sources of upper tropospheric NO
x
; however, there is a large spread in estimates of the global emission rates (2–8 Tg N yr
−1
). We combine upper ...tropospheric in situ observations from the Deep Convective Clouds and Chemistry (DC3) experiment and global satellite‐retrieved NO
2
tropospheric column densities to constrain mean lightning NO
x
(LNO
x
) emissions per flash. Insights from DC3 indicate that the NO
x
lifetime is ~3 h in the region of outflow of thunderstorms, mainly due to production of methyl peroxy nitrate and alkyl and multifunctional nitrates. The lifetime then increases farther downwind from the region of outflow. Reinterpreting previous analyses using the 3 h lifetime reduces the spread among various methods that have been used to calculate mean LNO
x
emissions per flash and indicates a global LNO
x
emission rate of ~9 Tg N yr
−1
, a flux larger than the high end of recent estimates.
Key Points
The upper tropospheric NO
x
lifetime is shorter than typically assumed
A shorter NO
x
lifetime improves agreement among various methods used to calculate mean lightning NO
x
emission rates per flash
Global lightning NO
x
emission rates are estimated to be ~9 Tg N yr
−1
Plain Language Summary
Lightning is an important source of upper troposphere nitrogen oxides; however, there is high uncertainty in the amount of nitrogen oxides produced from lightning. Using recent updates in upper tropospheric nitrogen oxides chemistry, this study decreases this uncertainty from a factor of 4 to less than a factor of 2 and shows that the amount of nitrogen oxides produced from lightning should be higher.
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