Abstract. An improved Gas and Aerosol Collector (GAC) equipped with a newly designed aerosol collector and a set of dull-polished wet annular denuder (WAD) was developed based on a Steam Jet Aerosol Collector (SJAC) sampler. Combined with Ion Chromatography (IC) the new sampler performed well in laboratory tests with high collection efficiencies for SO 2 (above 98 %) and particulate sulfate (as high as 99.5 %). An inter-comparison between the GAC-IC system and the filter-pack method was performed and the results indicated that the GAC-IC system could supply reliable particulate sulfate, nitrate, chloride, and ammonium data in field measurement with a much wider range of ambient concentrations. When applied in two major field campaigns (rural and coastal sites) in China, the GAC-IC system provided highquality data in ambient conditions even under high loadings of pollutants. Its measurements were highly correlated with data by other commercial instruments such as the SO 2 analyzer (43c, Thermo-Fisher, USA; R 2 as 0.96), the HONO analyzer (LOPAP, Germany; R 2 as 0.91 for samples from 15:00 to 07:00), a filter sampler (Tianhong, China; R 2 as 0.86 for SO 2− 4 ), and Aerosol Mass Spectrometer (AMS, Aerodyne, USA; R 2 above 0.77 for major species) over a wide range of concentrations. Through the application of the GAC-IC system, it was identified that 70 % of chloride and nitrate by the filter method could be lost during daytime sampling due to high temperature in the rural site of Kaiping. In Changdao field campaign (coastal site), though a particle dryer was applied, its drying efficiency was not well considered for the collection efficiency of AMS seemed still interfered a bit by local high relative humidity. If the inter-comparison was done with relative humidity below 50 %, the correlations ranged from 0.81 to 0.94 for major species. Through laboratory and field studies, this instrument is proved particularly useful in future intensive campaigns or long-term monitoring stations to study various environmental issues such as secondary aerosol and haze formation, as well as climate change.

This paper explores the role of the secondary inorganic aerosol (SIA) species ammonium, NH + 4 , nitrate, NO − 3 , and sulfate, SO 2− 4 , during haze and fog events using hourly mass concentrations of PM 2.5 measured at a suburban site in Hangzhou, China. A total of 546 samples were collected between 1 April and 8 May 2012. The samples were analyzed and classified as clear, haze or fog depending on visibility and relative humidity (RH). The contribution of SIA species to PM 2.5 mass increased to ∼50% during haze and fog. The mass contribution of nitrate to PM 2.5 increased from 11% during clear to 20% during haze episodes. Nitrate mass exceeded sulfate mass during haze, while near equal concentrations were observed during fog episodes. The role of RH on the correlation between concentrations of SIA and visibility was examined, with optimal correlation at 60%-70% RH. The total acidity during clear, haze and fog periods was 42.38, 48.38 and 45.51 nmol m −3 , respectively, indicating that sulfate, nitrate and chloride were not neutralized by ammonium during any period. The nitrate to sulfate molar ratio, as a function of the ammonium to sulfate molar ratio, indicated that nitrate formation during fog started at a higher ammonium to sulfate molar ratio compared to clear and haze periods. During haze and fog, the nitrate oxidation ratio increased by a factor of 1.6-1.7, while the sulfur oxidation ratio increased by a factor of 1.2-1.5, indicating that both gaseous NO 2 and SO 2 were involved in the reduced visibility. , 2014: Using hourly measurements to explore the role of secondary inorganic aerosol in PM 2.5 during haze and fog in Hangzhou, China. Adv.

To study the role of submicron particulate matter on visibility degradation in Shanghai, mass concentrations of PM 1 , secondary inorganic aerosol (SIA) in PM 1 , and SIA precursor gasses were on-line monitored during a 4-week intensive campaign in December 2012. During the campaign, 8 haze periods were identified when on average PM 1 mass increased to 62.1 ± 25.6 g/m 3 compared to 30.7 ± 17.1 g/m 3 during clear weather periods. The sum of SIA in PM 1 increased in mass concentration during the haze from 14.9 ± 7.4 g/m 3 during clear periods to 29.7 ± 10.7 g/m 3 during the haze periods. Correlation coefficients (R 2 ) of the visibility as function of mass concentrations of SIA species in PM 1 show negative exponential relations implying the importance of the SIA species in visibility reduction. The important role of ammonia in SIA formation is recognized and demonstrated. Generally, ammonium neutralizes sulfate and nitrate and the molar equivalent ratio of ammonium versus the sum of sulfate and nitrate increases during the haze episodes. Air mass backward trajectories introducing the haze periods show the impact of nonlocal ammonia on visibility degradation in Shanghai.