Abstract. Gaseous nitrous acid (HONO) is an important source of OH radicals in the
troposphere. However, its source, especially that during daytime hours
remains unclear. We present an instrument for simultaneous unambiguous
measurements of HONO and NO2 with high time resolution based on
incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS). To
achieve robust performance and system stability under different environment
conditions, the current IBBCEAS instrument has been developed with
significant improvements in terms of efficient sampling as well as resistance
against vibration and temperature change, and the IBBCEAS instrument also has
low power consumption and a compact design that can be easily deployed on
different platforms powered by a high-capacity lithium ion battery. The
effective cavity length of the IBBCEAS was determined using the absorption of
O2-O2 to account for the “shortening” effect caused by the
mirror purge flows. The wall loss for HONO was estimated to be 2.0 % via
a HONO standard generator. Measurement precisions (2σ) for HONO and
NO2 are about 180 and 340 ppt in 30 s, respectively. A field
inter-comparison was carried out at a rural suburban site in Wangdu, Hebei
Province, China. The concentrations of HONO and NO2 measured by
IBBCEAS were compared with a long optical path absorption photometer (LOPAP)
and a NOx analyzer (Thermo Fisher Electron Model 42i), and the
results showed very good agreement, with correlation coefficients (R2)
of HONO and NO2 being ∼0.89 and ∼0.95, respectively; in
addition, vehicle deployments were also tested to enable mobile measurements
of HONO and NO2, demonstrating the promising potential of using
IBBCEAS for in situ, sensitive, accurate and fast simultaneous measurements
of HONO and NO2 in the future.
Abstract. Nitrous acid (HONO) is a key determinant of the daytime radical
budget in the daytime boundary layer, with quantitative measurement required
to understand OH radical abundance. Accurate and precise measurements of
HONO are therefore needed; however HONO is a challenging compound to measure
in the field, in particular in a chemically complex and highly polluted
environment. Here we report an intercomparison exercise between HONO
measurements performed by two wet chemical techniques (the commercially
available a long-path absorption photometer (LOPAP) and a custom-built instrument) and two broadband cavity-enhanced absorption spectrophotometer (BBCEAS) instruments at an urban
location in Beijing. In addition, we report a comparison of HONO
measurements performed by a time-of-flight chemical ionization mass
spectrometer (ToF-CIMS) and a selected ion flow tube mass spectrometer
(SIFT-MS) to the more established techniques (wet chemical and BBCEAS). The
key finding from the current work was that all instruments agree on the
temporal trends and variability in HONO (r2 > 0.97), yet they
displayed some divergence in absolute concentrations, with the wet chemical
methods consistently higher overall than the BBCEAS systems by between 12 %
and 39 %. We found no evidence for any systematic bias in any of the
instruments, with the exception of measurements near instrument detection
limits. The causes of the divergence in absolute HONO concentrations were
unclear, and may in part have been due to spatial variability, i.e.
differences in instrument location and/or inlet position, but this observation may
have been more associative than casual.
Abstract. Mobile passive differential optical absorption spectroscopy measurements of SO2 and NO2 were performed in the Guangzhou eastern area (GEA) during the Guangzhou Asian Games 2010 from November 2010 to December 2010. The observations were carried out between 10:00 to 13:00 (local time, i.e., during daylight). Spatial and temporal distributions of SO2 and NO2 in this area were obtained and emission sources were determined using wind field data. The NO2 vertical column densities were found to agree with Ozone Monitoring Instrument values. The correlation coefficient (referred to as R2) was 0.88 after cloud filtering within a specific ground pixel. During the Guangzhou Asian Games and Asian Paralympics (Para) Games, the SO2 and NOx emissions in the area were quantified using averaged wind speed and wind direction. For times outside the games the average SO2 emission was estimated to be 9.50 ± 0.90 tons per hour and the average NOx emission was estimated to be 5.87 ± 3.46 tons per hour. During the phases of the Asian and Asian Para Games, the SO2 and NOx emissions were reduced by 53.50% and 43.50%, respectively, compared to the usual condition. We also investigated the influence of GEA on Guangzhou University Town, the main venue located northwest of the GEA, and found that SO2 concentrations here were about tripled by emissions from the GEA.
In the article by Sargen et al., an error appears in the P-value given in the last paragraph of the Results section. The sentence should read ''For the subgroup of white children who submitted saliva samples and were found to have FLG-null alleles, their distribution in the United States was not correlated with any of the climate variables (Pearson's coefficients o0.10, P40.05).'' The authors regret the error.
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